Biomechanics

The sequence of motor-neuron recruitment is determined by___________.

spinal mechanisms and NOT by higher regions of the NS---the brain cannot selectively activate specific motor units.

A hypothesis for why eccentric contraction produces greater force is due to what?

the most recent evidence suggests that the main component for this comes from the elastic Titin molecule discussed earlier. Briefly, force enhancement during eccentric activity results from an interactions between Titin, actin and myosin. As the actin filaments are pulled centrally in the sarcomere along myosin, the Titin molecule becomes bound, wrapped and twisted around actin as actin not only slides on myosin but the myosin head interactions literally twist actin causing it to be wound around Titin. This tightens Titin producing greater tension if the external load is overpowering an activated sarcomere and causing it to lengthen.

By convention, forces to the right will have a ____________ value and forces to the left will be assigned a _____________value.

positive; negative

How do we calculate pressure?

pressure=force/area

Human Osteokinematic Angular Movements are often Combinations of

swing and spin Note: we can perform the action in this photo because of combos of spin and swing

In connective tissues the extracellular matrix contains ______________ and macromolecules called ____________________. As we will learn shortly these both affect the flow of fluid within all connective tissues

water; proteoglycans

What is stiffness? Why is knowing a structure's stiffness important?

we define stiffness by the ratio of stress to strain. Something that is stiffer will resist deformation to a greater extent than a tissue that is less stiff. We can quantify stiffness by mathematically looking at the stress to strain relationship. Graphically, a stiffer material would exhibit a steeper slope than a less stiff material. Summary, so looking at a graph, if it has a steeper slope, the structure has more stiffness. If it is more stiff, it can better resist deformation.

External forces are related to the...

weight of the limb or external pushes or pulls from outside forces

Muscles in the body are at a mechanical disadvantage because they use 3rd class levers. But why might this be a benefit?

yet on the other hand, muscles in third class lever systems provide greater ranges of motion (distance) and velocities of the distal components of the limb.

The resistance to flow/shear is called

VISCOSITY

Which design specializations mechanically influence a muscle's function?

-Length of its fibers -Arrangement/orientation of its fibers

Define FORCE

A push/pull

If active contractile elements typically show somewhat similar tension vs. sarcomere lengths. Then why would some muscles be stiffer than others?

Connective Tissue Make-up & Architecture

Are connective tissues viscous?

Connective tissues contain the mechanical properties of flow of fluid, so yes, they are viscous, but they are also elastic because of the collagen they contain, so they are thus, VISCOELASTIC Viscoelasticity is a mechanical behavior in muscle, tendon, cartilage, or ligaments.

Static equilibrium in 2D offers the following info...

These equations characterizing static equilibrium involve two main assumptions: one, linear forces directly related to sum of the forces in the X and Y directions will be always equal zero and second the sum of the torques around any given single axis is also equal to zero.

How do we calculate work?

WORK=FORCE X DISTANCE OBJECT MOVED.

During DAY 2-4 of an injury to a ligament/tendon, what are the cellular responses?

Day 2-4: Cellular Stage Clot forms (erythrocytes, inflam. cells) Macrophages and fibroblasts invade the damaged area (remove debris and begin synthesis of a new CT matrix) Fibroblasts produce type III collagen Union is weak and fragile, ruptures with very low tensile stresses (stretching) Application: Protection from any tensile loads (NO TENSILE LOADS!)

What is FIRING RATE

FREQUENCY of signal RANGE OF FREQUENCIES= BANDWIDTH

During DAY 21-60 of an injury to a ligament/tendon, what are the cellular responses?

Day 21-60: Consolidation Stage Remodeling of collagen fibril organization Gradual decrease in # of fibroblasts and macrophages Union is progressively stronger Collagen fibrils increasing in diameter and more densely packed, fibroblasts slow collagen proliferation Increasing cross links as tissue is now becoming more stable and "less" responsive over time to treatment that aims to effect collagen organization Application: Progressively increase tensile forces via AROM/PROM Repetitive low tensile stresses remain helpful

During DAY 61-360 of an injury to a ligament/tendon, what are the cellular responses?

Day 60-360: Maturation Stage Primary strength from type I collagen. Tissue appears only slightly disorganized and hypercellular. Tissue is stable and union is stable. Poor (much less) ability to modify collagen organization therapeutically. Application of adequate stresses increases fibril density and covalent collagen cross linking. Application: More aggressive but progressive increase tensile forces via AROM/PROM & Resistive Exercises ****IN THE EARLY PART OF THIS PHASE TISSUE IS STILL NOT ABLE TO RESIST EXCESSIVE TENSILE LOADS .

Given the posture seen here what increases in muscle forces in the lower limb would be needed to maintain this alignment?

You are correct! There will be increased flexion torques at the knee and hip requiring greater forces from muscle opposing those torques which would come from the knee and hip extensors ; Knee extensors and hip flexors A

The angle between the brachioradialis m and radialis bone is 35 degrees. The resultant force is 88N. Calculate the normal and parallel components.

You can draw a paralelogram help you visualize.

Define VISCOELASTICITY.

Definition: time-dependent mechanical behavior where the stress response of the material depends on: -amount of time the strain is applied -strain RATE at which it was applied! -previous condition of the material (Hx) Most biological tissues are viscoelastic!

What is a MUAP?

Motor Unit Action Potential (MUAP) = summed electrical activity of all muscle fibers activated within the motor unit

Differentiate between CREEP and STRESS-RELAXATION.

Creep is an increase in plastic strain under a constant load. Summary, a structure that is exposed to a constant stress (external load) will eventually deform/enter plastic region. e.g old stained glass windows are thicker at the bottom than at the top because of the constant force of gravity. Thus, are the bottom of our bones thicker than the superior aspects because of creep? Stress relaxation is a decrease in stress under constant strain. A structure that deforms because it is held at a constant length for a constant period of time. e.g. holding a rubber band across two pins. If you take one pin out the rubberband will return to its original shape, but if you keep the rubberband wrapped around both pins for a constant amount of time, the next time you remove one of the pins, the rubberband will not return fully to its original shape.

Thus a single force whose line of action does not pass through the center of mass of the body will result in a

combination of linear and angular motions

More on Bone's componets

If we looked up close into bone we would observe that bone's collagen fiber are inner twined like the rebar of the bridge support. Calcium and other minerals are like the gravel of concrete and proteoglycans are the cement that binds everything together.

Describe if there would or would not be movement in the following cases: 1) Applied force= resistive force 2) applied force < resistive force 3) Applied force > resistive force

If: Applied force = resistive force then: no movement Applied force < resistive force then: no movement Applied force > resistive force then: movement scenario 3 is an example of unbalanced forces at work; e.g. when the upward force from a person is greater than the resisitive force from a barbell, we see it move.

What are the basic mechanical functions of TENDONS and LIGAMENTS

In addition to the notes in the image: Whether the structures are ligaments or tendons, from a biomechanical perspective, they are composed of dense connective tissue using parallel or closely parallel configurations of collagen fibers allowing them withstand very high tensile loads.

Define ROTATIONAL STABILITY

In review rotational equilibrium is achieved when the net external torques around a body or object is equal to zero. A body at rest will not undergo any angular displacement without the addition of an external unbalanced force. If an object or body is already rotating with a given velocity there would be no change in the angular velocity without the addition of an external force. Therefore, rotational stability is the resistance of a body or object to having its rotational (angular) equilibrium disrupted. In simple terms, rotational stability is achieved by a body having resistance against being rotated.

Define FRAGILE.

In terms of material properties a tissue such as bone is fragile when the amount of stress/strain, measured by the area underneath the curve is small. The bone tissue seen here on the left is fragile compared to the tissue on the right.

What else affects the stages of healing?

Individuals who are older, smoke, or are dealing with various endocrine disorders such as diabetes will typically demonstrate slower rates of healing.

Forces exist as a result of an __________________________.

Interaction

What do we call the ANGLES in BIOMECHANICS and PT? What do they refer to?

Intersecting lines = body segments Vertex = anatomical joint structures

Differentiate between ISOMETRIC, ECCENTRIC, and CONCENTRIC activation

Isometric activation occurs with production of a tensile or pulling force while the muscle-tendon length remains constant. Concentric activation of a muscle denotes the production of a pulling force during which the muscle-tendon length is decreasing (shortening). Eccentric activation of a muscle occurs with the production of a pulling force within the muscle however the muscle-tendon unit is actually lengthening.

If more motor units are recruites at a higher frequency, what is happening to amplitude?

It is HIGHER

How does ARTICULAR CARTILAGE withstand significant joint compressive forces, shearing, and deforming forces occurring at joints?

It is able to do both of these because of the presence of both COLLAGEN and AGGREGAN molecules within its extra cellular matrix. AGGREGAN molecules provide resistance to compression while COLLAGEN sustains the shape of the cartilage itself.

Define DAMPING

It slows down the rate of recovery back to resting length or shape after being deformed by an external load. In muscles and tendons this important material property allows smooth and controlled movements rather than jerky ballistic type motions if the muscle tendon complexes behaved as purely elastic materials. E.G. Memory foam is a good example of a material that exhibits high levels of damping. Press your hand into the foam and recovery of the material occurs but at a very slow rate.

What are the INFLUENCES on ARTHROKINEMATIC MOTIONS?

Joint Geometry Ligamentous Constraints Intervening Structures (e.g. menisci)

Define ARTHROKINEMATICS

Joint movement

What is the KEY to ANGULAR MOTION OF A RIGID BODY?

Key: All points of the object move at the same angle but do not undergo the same linear displacement

Describe Newton's second law.

LAW OF ACCELERATION The second law is basically stating that a body can only speed up or slow down if an external force acts upon it. "Acceleration of an object is directly proportional to the magnitude of the resultant forces acting upon it and inversely proportional to the object's mass." Acceleration= force/mass

Describe the organization of "WHOLE" muscles from inside out.

Muscle cells (fibers are surrounded by-->SARCOLEMMA-->ENDOMYSIUM-->PERIMYSIUM-->epimysium--> Note that forces from sarcolemma are being transferred all the way out to EPIMYSIUM. Note: the amount of connective tissue ultimately influences the mechanical properties of a muscle

Muscle force is increased through________________.

Muscle force increased through higher recruitment and increased rate coding of MUAPs

Is the length-tension curve the same for each muscle?

NO, because muscles have different resting lengths

How do AGGREGANS increase their COMPRESSIVE STIFFNESS?

Negative sites on Aggregans are pushed closer together: this increases their mutual repulsive force and increases compressive stiffness of the cartilage itself. Note: Imagine a bottle brush type appearance of Aggregan molecules with glycosaminoglycan molecules with very large numbers of negative charges along its brush hairs. Remember from chemistry that negative charges repel negative charges so as the brushes are pushed together from one joint surface pushing on the other, there is an electrochemical repelling force that attempts to resist its compression. Therefore, the electrochemical repulsive forces act to stiffen cartilage against external compressive loads.

What are the units of MECHANICAL STRESS?

Newtons per square meter

Define Normal Component (Normal Force)

Normal Component Fy Acts perpendicular to a bony segment Indicated as Fy or Fn Typically will cause a rotation of a bony segment e.g. like when you push cell phone to rotate, you had to push perpendicular to parallel force

Understand the horizontal, resultant, and vertical components in the image.

One of the first steps to take in analyzing a force vector is to determine its orientation in relation to a sensible frame of reference. In this case, our frame of reference is the ground which is horizontal. The ground reaction force vector you see here is oriented forwards at an angle. The individual limb segment at this point in the walking cycle is pushing downwards and backwards on the force plate so the reaction force from the ground is upwards and forwards. For our analysis, what we first determine the horizontal component of this vector and the vertical component of this vector. Here the horizontal and vertical components are identified by simply creating a right triangle with the ground reaction force vector as its hypotenuse. If we think about it, the hypotenuse is made up of the horizontal and the vertical components. Instead of hypotenuse, we use the term Resultant. The resultant force in reality is the combined effect of the horizontal push from the individual's limb against the force plate and the vertical downward push on the force plate that were recorded by the force plate. If you review the previous animation you see that the ground reaction force vectors are simply combinations of the horizontal and vertical forces on the plate. The horizontal and vertical components are going to be the opposite and adjacent sides of our right triangle when we try to analyze this force vector.

How do we calculate MECHANICAL ADVANTAGE?

Output force/input force

Which of the following types of joints would demonstrate only spin motion?

PIVOT!

With a forward head posture, which muscles, anterior or posterior, are under a higher demand?

POSTERIOR

Define PARALLEL COMPONENT

Parallel Component Acts parallel to a bony segment Indicated as Fx or Fp Causes compression or distraction between articulating surfaces

Which of the muscle architectural designs in the last slide is mechanically advantageous if the muscle needs to generate a large shortening excursion and also higher contractile shortening?

Parallel arranged muscle fibers are generally longer which supports speed and greater shortening excursion.

Define POWER.

Power = The RATE at which a force does work

What are the 2 types of TRANSLATION?

RECTILINEAR TRANSLATION: When all points move along straight lines CURVILINEAR: When the paths are curved

What is MECHANOTRANSDUCTION?

Process by which the human body converts mechanical loading into cellular responses Occurs through out the life span in CTs

Define: SPINNING

Pure Rotation Around a Fixed Axis (few human joints exhibit only spin) e.g. tire spinning on ice

How do we calculate the forces acting on a body that are in two different lines.

Put tails together and draw a parallelogram to determine the resultant force

Forces applied perpendicular away from a particular connective tissue's surface will be designated as

TENSILE LOADS

What is RATE CODING?

The Frequency of MUAPs Stimulated by Axon e.g. fast or slow

What is an AXIS (AXES)?

The Imaginary line (straight) around which rotation of a bone occurs perpendicular to it.

What is the composition of tendons and ligaments?

Tendons and ligaments are quite similar in composition but differ substantially in their collagen fiber orientation. Generally as with most musculoskeletal connective tissues they are composed mainly of water. By weight, 70% of ligaments and tendons are water, approximately 25% is type one collagen, with the rest consisting of glycoproteins and elastin. One overall compositional difference between tendons and ligaments arises from the observations that in general ligaments have greater amounts of elastin than tendons. Collagen fibers are arranged parallel to the long axis of the ligament or tendon. From a functional perspective, this parallel arrangement gives rise to structures that are generally very stiff and exhibit high tensile strength.

Define PRESSURE

The concept of pressure is used to describe force distribution. Pressure is defined as the force per unit area. Unit areas refer to a specific and defined geometric area. Unit areas can be in square (length x width) units such as centimeters, millimeters, inches, etc.

An illustration of the contractile elements of muscle

The contractile elements of muscles, the parallel and in series elastic components are mechanically illustrated here. Mechanically the passive components of muscles, because they behave elastically can be modeled as springs.

Define DISPLACEMENT

The distance and the direction a body has moved.

Describe the FLUID PHASE of ARTICULAR CARTILAGE.

The fluid phase at its simplest form is related to the flow of water in and through the cartilage. As water flows out from the release of bound water from Proteoglycan aggregan macromolecules during compressive loads the articular cartilage has less resistance to further compressive strain. The faster the flow of water out of articular cartilage the faster the deformation that occurs. Healthy cartilage controls the outflow so that cartilage is not rapidly compressed. However, constant compressive loads will lead to creep as the cartilage continues to deform slowly over time with greater release of unbound water moving out of the cartilage. This again demonstrates the viscoelastic property of creep in articular cartilage. :kEY NOTES: Faster flow of water out=faster flow of deformation;on the flip side, constant compressive loads will lead to slow deformation, CREEP

What can forces do?

The force may: 1. Produce motion 2.Stop motion 3. Change direction of the body 4. Positively accelerate the body 5. Negatively accelerate the body (decelerate the body)

Describe the FORCE-VELOCITY relationship.

The force-velocity relationship refers to the force actively generated by a muscle as a function of its shortening or lengthening velocities. During concentric and eccentric activations of skeletal muscles, a unique relationship exists between its maximal force output and its velocity of contraction (or elongation).

What is EMG?

The recording of a specific muscle's APs is called electromyography (EMG)

Give an example of when the mechanical axis and longitudinal axis align.

To make the mechanical axis concept a little easier to understand visualize your forearm rotation around your humerus as you supinate and pronate. The mechanical axis of this rotation can be pictured as a line coinciding generally with the longitudinal axis of the forearm and passing perpendicular to the center of the stationary joint's surface (the capitulum of the humerus).

The matrix frame that AGGREGATES are entrapped in is made up of what type of COLLAGEN?

Type II COLLAGEN that forms a meshwork of high tensile-strength fibrils as depicted in the diagram The entrapped proteoglycans attached to protein cores named Aggregans, extend perpendicularly from the hyaluronic acid backbone. These proteoglycans bind and trap large amounts of water.

Muscle tendon units have the ability to generate tensile force both _____________ and _________________________.

actively and passively

Where does the line of action of a muscle run?

from origin to insertion

Outside of chondrocytes, articular cartilage consists primarily of _____________________.

large hydrated proteoglycan aggregates

Most muscles of the body act as which class of lever?

Third

What does each letter of ARE stand for in the lever systems?

"A" stands for axis, fulcrum "R" stands for the resistance, weight force, external force and "E" stands for the effort or internal force.

When forces are parallel but in opposite directions they are often designated as a ___________________________

"force couple."

Define QUIET STANDING

"standing" is the human position in which the body is held in an upright position and supported only by the feet. Although standing often appears to be static, the body sways slightly back and forth in the sagittal plane. The sway that occurs, in what we can call "quiet standing", is often likened to the motion of an inverted or upside down pendulum. Mechanically, the concept of sway involves the BCOM rotating over an uneven arc forwards, backwards, and side to side. Interestingly, the body controls any small perturbations of the BCOM by making small adjustments through modifying the location of the center of pressures (C.O.P) under each foot

How do you calculate the rate of change in length or velocity of a muscle fiber?

# of sarcomeres x average shortening velocity of sarcomeres Thus, If you have a greater number of sarcomeres aligned in-series with each other, when stimulated, the greater the change in length and thus the greater the rate of change of the fiber. Now consider the question earlier, why have a brachioradialis muscle? Perhaps one reason is that it is a longer muscle with longer fibers than the other elbow flexors. An argument could be made that this muscle is built for speed.

Contractile force results from________________.

, contractile force results from the interactions of actin sliding centrally on myosin and approximating the z lines closer together. Next we will review this up close.

Define STANDING BALANCE

, we could define standing balance as the ability to control the center of gravity over the base of support in a given sensory environment. Note how posture and balance are intimately related.

What is ISOINERTIAL strength?

-Can be calculated by multi-modal computerized robotic type dynanometers -These types of instruments can also measure what is termed isoinertial strength, which involves assessing the force of a muscle or muscle group under a constant load. The parameter of peak force magnitude, average force over time or during changing joint angles can be collected on these devices. The rates of force development can also be collected for each muscle group during either static or dynamic conditions. Instrumentations such as these provide much more detail in the performance of a set of muscle groups than manual muscle testing or hand held dynamometers. Consider what limitations these instruments possess? Click the link to explore muscle strength and power assessment

Why is damage to CARTILAGE after age 30 significant?

-Cartilage is the connective tissue that declines the most after 30. -Since it is aneural, you cannot feel if you are loading or not loading it enough -since it is avascular it is therefore has a limited vascukar supply and cannot be reproduced quickly like when you were young...

Lever system contains 5 components. What are they?

-FULCRUM -WEIGHT (RESISTANCE OR EXTERNAL FORCE) -FORCE (EFFORT OR INTERNAL FORCE) -WEIGHT ARM -FORCE ARM

What are PROTEOGLYCANS and GLYCOPROTEINS?

-Highly hydrated proteins that lie between the collagen and fibers that make up connective tissue. -They hold onto a large amount of water molecules -provide a significant role in the material properties of cartilage, bone, tendon, and ligament

Physical Therapists use goniometers as a means to measure angles between limb segments such as the femur and tibia or the humerus and forearm. Are these type of kinematic assessments using a relative or absolute frame of reference?

-Relative frame of reference -An absolute or global frame of reference is essentially motionless. If we use vertical or horizontal lines related to the earth as our frame of reference and these are motionless and therefore "absolute". When we utilize goniometers our reference is not necessarily motionless. For example we can place the thigh in may different angles relative to the ground when we measure the knee angle.

Explain the graph on the next slide.

. Note that as the length of the sarcomere increases, the addition of a passive force appears to give rise to greater force potential than was seen with just the active cross bridging model. Let's explore where this passive force comes from

Name the three vertical forces acting on the radial-humeral and ulnar humeral joints in the following picture.

1) Rotatory component 2) Vertial joint force (the humerus is pushing down on the forearm at the joint to keep it from going up at the elbow. 3) Gravity of the forearm weight Note: if you know two out of three of the forces, you can calculate the third, because they should equal 0 (or cancel each other out if they are in static equilibrium)

What are the fundamental elements that comprise connective tissues?

1. Cells 2. Extracellular Matrix: -Fibrillar: a. components b. Collagen Elastin -Interfibrillar components (a.k.a. ground substance): a. Glycoproteins and proteoglycans Glycosaminoglycans, (GAGs) b. Mineral deposits Note: Consider that bone tissue and tendon tissue contain the same basic components but not in the same arrangement and certainly not in the same proportions.

To Alter Torque, (moment), There Must Be A Change In At Least One Of These:

1. Length of the moment arm 2. Amount of force applied to the moment arm (AKA magnitude of applied force)

What are the functions of ADULT HYALINE CARTILAGE FUNCTIONS?

1. Provides the bearing surface of synovial joints. 2. Increases surface loading area and can transfer enormous forces relatively evenly from one subchondral bone plate to another. 3. Under physiological conditions it provides an almost frictionless gliding surface.

The Mechanical Behavior of a Muscle to Elongate and to Generate Contractile Force Depends Directly On:

1. The amount, the architecture, and the make up of its CT 2. The length of the whole muscle tendon unit

Which three components are key to the success of structures withstanding external forces?

1. The mode of loading (load=force): -compressive -tensile -shearing 2. The size and shape of the components that make up the structure: -lengths -cross section -angle 3. The materials/what are the components made of: -e.g Connective tissue

Which of Newton's laws does the description below describe? If a body or an object is at rest, it will stay at rest until an unbalanced force acts upon it. A body or object will stay in motion until an unbalanced force acts upon it.

1st Law (Law of Inertia)

Define BRITTLE

A brittle material is one in which there is little plastic deformation strain prior to failure whereas a ductile material is one that demonstrates a larger amount of plastic deformation as a response to an external load before failing.

Define DUCTILE

A brittle material is one in which there is little plastic deformation strain prior to failure whereas a ductile material is one that demonstrates a larger amount of plastic deformation as a response to an external load before failing.

Define MOTION

A change in position with respect to a reference point.

In which lever system is the distance from the load to the axis always longer than the distance of the effort force to the fulcrum?

Third class levers

How do I know the arrangement of each lever?

ARE 1st class: rAe 2nd class: aRe 3rd class: aEr

Describe "The Moment Arm"

AKA "TORQUE" arm The moment arm is the perpendicular distance from the line of action to the axis of rotation. The greater the distance, the greater the magnitude

How does a muscle generate force ACTIVELY and PASSIVELY

Active force generation occurs within substructures of muscle cells named sarcomeres. Sarcomeres are characterized as the functional unit of active force generation of a muscle; sarcomeres require the input of energy to create a pulling force. However, muscle tendon units contain important connective tissues running in-parallel and in-series with sarcomeres that demonstrate elastic behaviors during longitudinal strain (stretching) and contraction. This elastic behavior can produce work independently of the sarcomere's active force generation and this force is generated passively. Passive force generation occurs through the intrinsic resistance of the muscle and its connective tissues to deformation; such as when a muscle tendon unit is elongated by a load there will be an increasing resistance to deformation. The connective tissues with increasing internal resistance (stress) are in essence absorbing energy and this stress energy will return back to the tissues when the load is released.

What happens to collagen in the ELASTIC REGION?

After the waviness of the internal collagenous structures are completely eliminated further tensile load on the ligament demonstrates a linear relationship between the amount of strain and the internal resistance to the external force (region B on the graph). In this range, the ligament is deforming and internal stress is increasing and like the toe region, if the load is removed the ligament returns all the way back to its wavy form. Thus in this range as well, the ligament is still behaving like a purely elastic material.

Give an example of Brittle v Ductile

Aging bones become more brittle and therefore fracture easily. A child's bones give in to more plastic deformation (like compressing a plastic bottle) before they are subjected to failure.

How else does ARTICULAR CARTILAGE respond to COMPRESSION FORCES?

Also note that Aggregans in hyaline cartilage have a high affinity for water and thus bind tremendous amounts of water molecules to themselves. When energy is imparted to these macromolecules during compressive loading energy tends to cause the release of some of the water molecules from its many glycosaminogylcans macromolecules. Because articular cartilage is somewhat porous to water, fluids are able to move in and out of the cartilage through its surface, similar to water moving in and out of a dense and compacted sponge when the sponge is compressed and then released. Compressive loads tend to drive water out of cartilage in a rate dependent manner through its microporous surface. Because water is flowing through cartilage, any internal mechanisms that provide resistance to the flow of water lead to changes in the flow rate and thus provides viscous element to cartilage's viscoelastic properties. Cartilage therefore has elastic properties from its collagenous fibrils and viscous properties from the resistance of flow of water moving in and out. Note: Mechanical Response strongly tied to fluid flow in and out of the cartilage There is fluid flow through the tissues and across the surface when cartilage is deformed. Cartilage is a mixture of solid and fluid components and therefore considered Viscoelastic: -Creep -Stress-relaxation

In regard to EMG, What is the effect of velocity (slow vs fast) on the amplitude of the signals?

Amplitude represents the number of motor units recruited during a contraction and motor units fired/activated

Define MECHANICAL AXIS

An axis that allows angular motion around it. Our previous example of a door hinge to represent an axis for rotation of bones is straight forwards and we can utilize a term called the mechanical axis to characterize a bone's axis for angular motions. The true mechanical axis of a bone refers an axis which typically passes through the joint center. This axis may coincide with the moving bone's longitudinal axis or in some cases it does not pass through the bone's longitudinal axis.

Where is the base of support located?

An object's base of support is the entire area bounded by the perimeter of the surface it is contacting. Observing the diagrams here gives you a clue that the base of support at times is not simply the points of contact but can include the area that is represented by the dotted lines. The circle with an x represents the COG projection onto the ground surface.

Anular velocity equals...

Angular velocity [omega or w]=Theta/Time(f)-Time(I)

How does ARTICULAR CARTILAGE get its NUTRITIENTS

Articular cartilage lack blood vessels and receive nutrients from the surrounding synovial fluid. Chondroctyes are the cellular factories that create the components of the extracellular matrix of proteins necessary for maintenance and repair and they require adequate nutrition to do so. Cyclic loading across the surfaces of articular cartilage appears to be the main mechanism for nutrient and waste exchange. This gives importance to maintaining proper mobility and function in terms of articular cartilage metabolic processes. Loading and unloading through joint motions provide the energy to push local fluids and nutrients in and out of specific areas in cartilage during normal activities. LOTION IS MOTION! Get their nutrients through movement

What is the molecular composition of ARTICULAR CARTILAGE?

As can be seen here, cartilage is predominantly composed of water with the other main components of proteoglycans and type 2 collagen. Recall that in capsules, tendons, and ligaments, the main type of collagen is type I. Later we will see that types 1 and 2 collagen each present with some important differences in the response to external tensile loads.

Articular Cartilage is primarily made of what type of collagen? How does this type of collagen differ from others?

As compared to type 1, type 2 collagen is weaker and demonstrates no plastic range. This suggests that type 2 collagen behaves as a brittle material, failing abruptly when strain or stress levels are exceeded.

Describe the ELASTIC REGION on the stress-strain curve

As related to mechanics, when a material returns back to its original shape after it has been loaded and unloaded the strains or deformations which occurred are elastic in nature. It is important to realize that all connective tissues of the body have some level of elasticity; even bone is elastic. Up to the point marked with an X this hypothetical ligament or tendon will return back to zero strain if the external load is removed.

What occurs in the "toe region" of the stress-strain curve. What happens with collagen in this region?

As the ligament first begins to undergo a tensile force there is little change in the internal resistance to the load but a significant amount of deformation. This is referred to as the toe region of the curve. As you will learn, a ligament's main component is collagen and collagen without any external load on it tends to exist in a shape that is rather wavy or crimped in nature. This waviness, as seen in location A on the graph, can easily be lost with only a little tensile force. Therefore, there is little internal resistance or stress and the ligament deforms easily. But if tensile load removed, it will return to its original shape.

What is the relationship between TITIN and sarcoeres?

As the sarcomere is lengthened, a structural protein called Titin which displays elastic mechanical behaviors, provides some resistance to passive stretch of the sarcomere. While Titin does not contribute to the active force generation and is considered more of a structural protein rather than an active contractile protein it plays a secondary role in force generation. Titin is an incredibly large macromolecule running along the myosin filament running from Z line to M line. As the Z lines move apart when the sarcomere is stretched, elastic type tension develops within this protein. Thus, it is generating resistance to elongation of the sarcomere and adds to the force generation of the sarcomere. When muscles are stretched, the giant protein titin develops passive force. Titin's tensile force functions to maintain the structural integrity of the sarcomere. While the stretching of the muscle's connective tissue including its tendons provides resistance to a muscle being stretched, Physical Therapists need to realize that a large part of the passive forces generated by muscle cells are developed by the elastic protein Titin. For Physical Therapists, recent studies have identified different genetic forms of Titin with evidence that these different forms may play a role in the extensibility and stability of a muscle across certain myopathies and dystrophies.

What is a spatial from of reference?

Attempting to describe the motions of a body accurately requires a spatial frame of reference. This frame of reference allows both the position and the direction of a body's motion to be defined relative to a known location.

Define LONGITUDINAL AXIS

Axis passes through LONGITUDINAL PLANE The longitudinal axis refers to the long axis of a bony segment. Physical Therapists utilize the longitudinal axes of bones as references when measuring the active or passive range of motion of a joint.

What is OSTEOKINEMATICS?

Bone movement The physiologic movement possible at each joint occurs when forces act on a bone to move it. Osteokinematic movement describes how each bony joint companion moves relative to the other relative to the three cardinal planes of the body.

Describe the organization/order of bone?

Bone tissue is very highly ordered making it strong, stiff, but more brittle than any of the other connective tissues of the musculoskeletal system.

Describe STATIC EQUILIBRIUM

But even if external forces are applied to an object a state of mechanical equilibrium can exist when both the net linear forces and moments or torques acting the object equal zero. As per Newton's first law of motion, an object or body is in equilibrium when it is either at rest which we refer to as static equilibrium or when the object or body is moving with a constant velocity. An object or body moving at a constant velocity and in the same direction characterizes a state of dynamic equilibrium. In other words equilibrium is a state of zero acceleration where there is no change in speed or direction of a body.

What are the rules of a 3D coordinate system?

By convention in a 3D coordinate system the arrow heads are pointing towards positive values and follow the "right hand rule".

Define KINETICS

By definition kinetics is the study of the relationship between the motion of a body and the forces acting upon them.

Forces applied perpendicular towards a particular connective tissue's surface will be labeled as

COMPRESSIVE LOADS

More on CARTILAGE

Cartilage can absorb energy but also functions mechanically to transfer forces form one bone to another. Remarkably it also provides an almost frictionless gliding surface. Similar to tendons and ligaments mechanical loads effect the activity of cartilage cells, named chrondrocytes, through the processes of MECHANOTRANSDUCTION.

What is the COLLAGEN ORIENTATION IN TENDONS

Careful examination of the orientation of collagen fibres within the different ordered structures reveals that there are an abundance of parallel oriented fibers but also fibers that cross each other 3 dimensionally in unique and complex arrangements. The collagen in tendons are bound together with various proteoglycans. These proteoglycans are interwoven with the collagen fibrils and connecting fibrils together in a complex 3 dimensional fashion. Similar to ligaments, the mechanical properties of a tendon are largely dependent on the collagen fiber sizes and orientations and relaxed fibers appear to have crimps or waviness to them.

Clinically, why should PT's understand immobilization?

Clinically, Physical Therapists should clearly understand that immobilization has not just a negative effect on muscle mass but can markedly decrease the mechanical capacities of tendons and ligaments. Individuals immobilized for prolonged periods need progressive reloading of their tendons and ligaments before subjecting them to even the normal everyday loading activities.

What values are COUNTERCLOCKWISE AND CLOCKWISE motions given?

Clockwise motions are given a negative value and counterclockwise motions are given a positive value.

Define GENERAL MOTION.

Combo of LINEAR and ANGULAR motion

Briefly describe the Inorganic components and collagen of bone

Compared to engineering/bridge design: In bone, the inorganic components can be described as the concrete........giving bone its ability to resist compressive forces. The collagen is the rebar, giving bone the ability to resist unwanted bending forces.

What is the FUNCTION fo CONNECTIVE TISSUE in MUSCLE?

Connective tissues in muscles function to transfer force and store energy that can be used functionally.

Posture can be characterized _______________ and __________________

DYNAMICALLY and STATICALLY

During DAY 5-21 of an injury to a ligament/tendon, what are the cellular responses?

Day 5-21: Fibroplasic Stage Matrix and Cellular proliferation stage Scar is very cellular, (macros, mast, fibroblasts) Continued increase in collagen synthesis but now also degradation as collagen remodeling begins towards the end of this phase. Collagen fibrils beginning to enlarge Application: Ideal time to begin low tensile loads (can apply for about 3 wks) typically through controlled SLOW PROM from the Therapist! Low tensile stresses helpful to organize/align collagen fibrils

What are the EFFECTS OF PROLONGED and EXERCISE INDUCED LOADING on ARTICULAR CARTILAGE?

Does increased activity truly modify cartilage like it does with bone and muscle? While there is evidence of an adaptive response morphologically in children, prolonged loading does not result in significant changes in size of adult articular cartilage. Prolonged loading does appear to result in modest increases in the glycosaminoglycan concentration there does not appear to be changes in collagen content. Overall mechanical stimuli do not seem to influence adaptive changes to the same degree as in muscle, tendon, or ligament. Hypothetically, cartilage that enlarge in thickness would negatively effect the capacity for full joint range of motion and ultimately affect function. However, there does appear to be mechanosensativity to chondrocytes as they increase synthesis of GAGs in response to chronically higher compressive loads. Increased number of GAGs would support greater cartilage stiffness.

What is the effect of the type of muscle activity (eccentric vs concentric) give the same external load? Which is more efficient?

During the eccentric contraction, a greater force is created but fewer motor units are recruited. During concentric contractions, more motor units are recruited but the force created is less, making concentric contractions less efficient.

Describe DYNAMIC POSTURE

Dynamic posturing refers to the alignment of body segments during motion. During dynamic functional activities such as walking, running or just lifting an arm, the orientation of the body segments relative to each other and to vertical are considered with dynamic posture analysis.

Describe some characteristics of FRAMES of REFERENCE

Earlier we learned that kinematic frames of reference can be local or global in nature. Now as we deal with force vectors we can also consider frames of reference which can be related to: 1) vertical and horizontal directions, 2) the planes of the body, or 3) parallel to the long axis of a body segment or perpendicular to the body segment. Click on the link here to learn more about "funny" oriented vectors.

In regard to the musculoskeletal system, what are EXTERNAL FORCES?

External forces also act on the musculoskeletal system and these are forces coming from outside the body. Gravity is a key external force acting on the body. The picture here demonstrates the internal (biceps force) and external force (mass of the forearm).

Whata re COLLAGEN PRODUCING CELLS in the body?

Fibroblasts: connective tissue matrix Chrondroblasts/ chondrocytes: in cartilage Osteoblasts: in bone Skeletal muscle cells: in skeletal muscle Smooth muscle cells: in BVs and some organs

The GHJ has the following motions: FLEX/EXT ABD/ADD ER/IR Which would describe as OSTEOKINEMATIC SWINGS AND WHICH ARE SPINS?

Flexion extension and Abduction and Adduction would be swings whereas external and internal rotations are considered spins. Note how ER/IR is on a fixed axis

How does creep relate to physical therapy?

For Physical Therapists the take home message is that viscoelastic materials continue to elongate when stretched even when you do not increase the stretching force on them. Creep importantly is reversible as long as the strain did not fall into the plastic range, in other words you did not exceed the tissue's elastic range. The return to resting length is not instantaneous and is also a function of time.

What factors affect STABILITY?

For an object like the human body what factors or variables affect its stability. In nearly all objects, their stability will be influenced by their mass, the frictional forces between the objects and opposing contact forces and the vertical height and horizontal position of the object's COG/COM with respect to its base of support. E.G. think about standing on ice v standing on marshmallows

Define GROUND REACTION FORCE

From Newton's laws of motion we know if there is a force against the ground the ground applies an equal and opposite force to the body. This force from the ground we term the ground reaction force and since it is a force we will characterize it by its direction and magnitude. Note from the image: The red arrows in the drawing here represent the instantaneous average location of the ground reaction forces during standing under each limb (blue arrows). Note that when two feet are on the ground the ground reaction force vectors from each limb can be averaged to a single vector. We will see shortly that the location of the GRF is related to a mathematically calculated location termed the center of pressure

What is a MUSCULOTENDINOUS JUNCTION?

From anatomy course the anatomical connection between the muscle cells and the tendon of a muscle is referred to as the musculotendinous junction. The musculotendinous junction incorporates folds of each muscle cells into tendon's collagen fibers.

Human motion is usually what type of motion (general, angular, or translatory)?

GENERAL

Ground reaction forces originate from where?

GRF vectors originate from a location called the center of pressure (COP) during both static and dynamic standing activities.

How do we orient the X,Y axis?

Generally it is common to orient the X axis parallel to the segment or body you are interested in.

What are FACTORS that influence EMG signal?

Geometrical & Anatomical Factors: Electrode size Electrode shape Thickness of skin and subcutaneous fat Alignment between electrodes and fiber alignment Physiological Factors: Blood flow and temperature Type and level of contraction Muscle fiber conduction velocity (pH changes with fatigue) Number of motor units (MU) Degree of MU synchronization?

Define GRAVITY

Gravity is the force of attraction between bodies or objects that have mass. Gravity exerts its force in such a way that all the weight of a body/object "seems" to be concentrated at a single location point.

Does a large PCSA have an effect on muscle shortening?

Has a small effect. Generates high force but is slow.

How does having architechtural specializations relate to the nervous system?

Having architectural specializations relieves the nervous system from having to exert even more complex systems in order to control joint motions and postures.

Describe what you see in the following chart

Here in this diagram you are observing a plot of the velocity of shortening and the force generating potential of the muscle when it has been stimulated. Note that as the external load decreases the shortening velocity of the muscle can increase. Saying this in another way, as the velocity of shortening increases the amount of the external load that can be moved decreases. Force generation rapidly drops as contractile velocity increases. Intuitively we know this for when we lift a heavy object, we are challenged to be able to lift the object if we try and do it quickly. We can generate greater forces in our muscles when there are slower contractile velocities.

More about TITIN

Here is how Titin is thought to act within the sarcomere. As a muscle is stretched and the sarcomere is initially elongated Titin is stretch elastically like a coiled spring. As elongation continues Titin continues to stretch but also winds around the Actin filament stiffening it and thus resisting further elongation. In summary so far we have discussed the active force generation by sarcomeres in review of the sliding filament theory. Additionally, the sarcomere possesses the ability to generate passive tensile force when elongated that protects the sarcomere from over extending and adds to the overall tensile force generation of the individual sarcomeres. Muscles possess thousands of muscle cells and tens of thousands of sarcomeres with the potential for each to generate contractive force. In the next section we will explore the connective tissue organization of the muscle tendon unit and learn how these tissues are important to the overall force generation of every muscle.

Why do pennate muscles produce greater force? What is a consequence of their orientation?

How can this design generate more force? Consider this analogy. Imagine each muscle fiber as a person pulling on their own individual rope attached to the tendon. When each person pulls on the rope the sum of all of the individuals pulling, side by side, next to each other will be the total pulling force on the tendon. The more individuals pulling the greater the total force. By packing in more fibers with a pennate arrangement, the muscle is able to incorporate more individual muscle fibers into itself, and therefore can generate a greater contractile force. Thus, pennate muscles are designed as a mechanical means to potentially generate more tensile force on the tendon. However, the trade off is that the muscle fibers in a pennate arrangement are shorter as they are not spanning the length of the muscle as would be seen in a fusiform muscle such as the Sartorius muscle. The consequence of short fibers is that there is lower velocity of shortening of the whole muscle

What occurs in the PLASTIC REGION (non elastic region)? What happens to collagen

However, as the external tensile load keeps increasing there is a point where the graph departs from being linear and it appears that the stress-strain relationship begins to significantly change. The external load has now started to "break" some of the collagen fibers within the ligament structure and this is termed microfailure. Collagen is the main component of a ligament that resists tensile loads. The point where this occurs is denoted as the yield point of the material. Collagen fibers are breaking in a stochastic manner, with weaker fibers giving way before stronger fibers. After this point and up to the point of failure the material continues to undergo deformation but if you completely remove the external tensile load the tissue will not go all the way back to its original shape and thus it is not behaving as a fully elastic material because its internal structure as undergone microfailure as it is unable to complete return itself back to its original shape. This region is often referred to as the plastic region of a stress strain curve. From a clinical standpoint, ligaments operate within the toe region and first part of the linear elastic range during day to day functional activities.

How are TENDONS organized/structured?

Human tendons are connective tissues which posses a complex and highly ordered structure. Groups of collagen fibers are organized into primary bundles, primary bundles are organized into a second ordering process termed secondary bundles, and secondary bundles are organized into tertiary bundles. Primary and secondary bundles are surrounded by a loose collagenous connective tissue layer called endotenon while tertiary bundles are surrounded by a loose connective tissue layer named the epitenon and a second layer of fatty areolar connective referred to a the paratenon.

When discussing activation, a muscle is considered activated when it is being stimulated by the nervous system. Stimulation from a motor nerve, activating a healthy muscle produces contractile forces giving rise to which three different functional effects?

ISOMETRIC, CONCENTRIC, and ECCENTRIC

What is the relationship between IMMOBILIZATION and ARTICULAR CARTILAGE?

Immobilized joints show cartilage atrophy: Nutritional consequences Evidence surrounding immobilized joints reveals that cartilage overall appears to demonstrate some atrophy. To Physical Therapists, understanding that immobilization in effect can weaken articular cartilage, supports the paradigm that early controlled movement, when possible, confers benefit to cartilage just as it does with other connective tissues.

Characterizing the changes in force over time is identified as _____________________.

Impulse units Newton seconds

Increased TENSILE LOADING to a TENDON or LIGAMENT leads to____________.

Increased tensile loading leads to: (via mechanical, chemical, or electrical signals?) Addition of collagen fibrils, (increased metabolic production from fibroblasts and tenocytes) Increases in covalent bonding between collagen molecules.

What is the relationship of a high BMI and balance?

Individuals with high BMIs appear to demonstrate greater postural instability standing on one leg than their lean counterparts. They have greater difficulties in maintaining the "current" state of rotational equilibrium. When taking into account the relationship of mass and rotational inertia this makes sense. More external forces are needed to maintain rotational equilibrium with objects having more mass. Once the body's COM begins moving in a specific direction, it will continue moving unless an unbalanced muscular or other force resists it. The relationship between very high BMI and balance is something all therapists should understand in order to help prevent falls and injuries in their patients.

Define INERTIA

Inertia is the resistance of any physical object to any change in its state of motion!

Describe NEWTON'S 3RD LAW.

LAW OF ACTION-REACTION -To every action there is always opposed an equal reaction. (Forces never act in isolation on an object, they always come in pairs.... consider this when analyzing human motion) -states that in every interaction, there is a pair of forces acting on the two interacting objects/bodies. Note: Forces and counterforces are equal and opposite but the results on each may not be the same. If force equals mass x acceleration then for example the person jumping force and the earth's force must be equal. The mass of the earth is exponentially larger than the person, thus the acceleration of the earth is very, very small compared to the acceleration experienced by the person.

When a force's line of action passes directly through the center of mass of a rigid body, only ____________ motion is possible

LINEAR

In OSTEOARTHROSIS, what is the overall factor?

LOADING RATE! Note: From a clinical aspect, evidence of an association with higher compressive loads are not as robust as the evidence supporting models which describe higher loading rates as perhaps the most important overall factor.

The two most factors creating large amounts of torque to occur across joints through muscular contractions are?

Large PCSA and Moment Arm Lengths.

Describe Newton's first law

Law of Inertia. If a body or an object is at rest, it will stay at rest until an unbalanced force acts upon it. A body or object will stay in motion until an unbalanced force acts upon it Thus, A Force is needed to begin a motion or change the direction of an object (i.e a limb segment, trunk etc).

Understand the image describing the biomechanical stress-strain relationship of ligamentous tissues.

Lets now take the stress-strain curve and apply it to the clinical presentation of individuals at varying levels of strain to the Anterior Cruciate Ligament. Here is the same curve but with the added generalizations of the clinical presentations that might be observed with increasing deformation of the ligament in daily activities and with injury. On the Y axis is the load on the Anterior Cruciate Ligament and the X axis represents the percent deformation of the ligament. For the Anterior Cruciate Ligament daily functional activities typically place strains of up to approximately 3-4%. Daily activities including exercise place external tensile loads mostly in regions 1 and 2. Individuals can occasionally, with heavy exercise or activity, stress the ligament physiologically so that deformation occurs into the initial region of plastic deformation. Individuals in the early part of region 3 may experience a little soreness but with rest from the activity, symptoms rapidly decrease and the mechanical properties will most likely return back to normal. However, greater strains, such as those that might come with an injury into region 3 will result in greater plastic deformation and typically more significant inflammation and pain. Clinical assessment does not reveal any significant joint instability yet as the ligament, while weakened still appears to clinical test out normally. However, if the injury had taken the individual past 6%, strain, note the dip in the graph in region three. The internal resistance of the ligament has been reduced, enough fibers have failed to the point where the internal resistance is dropping off rapidly instead of continuing to rise. In this injury the Physical Therapist may now be able to clinically observe joint instability as well as increasing pain from the excessive deformation prior to complete failure. If the individual had sustained an injury above 7% the ligament would most likely have reach the maximum failure strain, there would be clinical signs of joint instability in the knee and the individual would have initially experienced considerable pain. So in summary, while obviously we can not test the stress strain relationship of a ligament in a clinical situation, knowing the biomechanical stress strain relationship of ligamentous tissues and how it could arise to the various clinical presentations is very important for Physical Therapists.

Do all ligaments have the same molecular composition?

Ligaments throughout the body are certainly of different sizes and shapes but importantly they have different molecular compositions. As a consequence of both variations in size, shape, biochemical make ups and collagen orientations ligaments will display quite unique mechanical properties. This graph shows the various molecular components of the tibial collateral of the knee. Compared to the tibial collateral ligament, the anterior cruciate contains more than twice the percentage of glycosaminoglycans. (GAGs). While tension is mainly resisted by collagen and elastin fibers GAGs also seem to play a part in transmitting and resisting tensile stresses by interacting with collagen fibrils. Therefore it is important to realize that ligaments have very defined functions, their intrinsic mechanical behaviors vary depending upon what they are made of

Define Line of Action

Line of Action ("imaginary" extension of the force in both the + and - direction to provide the force's geometric orientation)

What are the units used for Velocity and Acceleration

Linear Velocity (v) Distance/sec m/s, cm/s Linear Acceleration (α) Velocity/sec m/s2, cm/s2 Angular Velocity (ω) Change in angle/sec degree/s, radians/s Angular Acceleration (α) Change in angular velocity/sec degrees/s2 radians/s2

OSTEOARTHROSIS is due to what?

MECHANICAL FAILURE of ARTICULAR CARTILAGE

We delineate forces as VECTOR QUANTITIES which are characterized by_____________ and __________________.

Magnitude and direction

WHAT DETERMINES THE LOCATION OF THE SYSTEM'S COM?

Mass Distributions - static equilb. Lengths of Body Segments Center of Mass of Body Segments

LARGER MASS translates into

Mass is always a factor of stability. Remember that Newton's second law states that a greater force must be applied to a more massive object or body in order to achieve a given acceleration. Larger mass translates into greater rotational inertia! A greater external torque is need with any object with greater inertia to change it given rotational acceleration.

Differentiate btw MASS and WEIGHT.

Mass is the measure of the amount of matter that an object has and it is typically expressed in kilograms. However, In the English system, mass is often expressed in pounds. If you know an object's mass in pounds, simply multiply it by .45 to find the mass in kilograms. A 1 kilogram of mass weighs (based on earth's gravitational acceleration of 9.8 meters per second squared is approximately 2.2 lbs. For our purposes of this course please remember to convert "weight" measurements into kilograms of mass.

Define MECHANICAL ADVANTAGE

Mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it. Note: If the calculated value is greater than 1 a mechanical advantage exists. If the value is less than one a mechanical disadvantage is present.

What are the MECHANICAL PROPERTIES OF COLLAGEN FIBERS?

Mechanical properties Tensile stiffness (elongate <10%) High Strength High magnitudes of stress required to fracture Little direct resistance to compression due to small ratio of length to thickness Higher resistance to shear > elastic fibers Biomechanically collagen as a macromolecule exhibits high tensile strength, however it provides little resistance to compressive forces.

Tissue behavior is highly dependent upon the tissue's __________________ and _________________.

Molecular composition AND structure

How do you calculate MOMENTUM?

Momentum = mass x velocity

Define CURVILINEAR TRANSLATION

Motion along a curved line or path in which all parts of the system move in the same direction over the same time

Define TRANSLATORY movement.

Motion in a straight line Key: All points of the object move the same distance over the same time.

What are basic clinical Factors Physical Therapists Consider When Evaluating Muscle Performance? Is there an assessment tool that can quantify each at once?

No there isn't one that can quantify each at once. See image for the factors. Also note: An MMT is limited to identifying the factors. E.g. it can't tell when a muscle is turned on/off during a movement, etc.

Is standing upright an example of static equilibrium?

No, it is postural sway

How do we calculate STRAIN?

Normalization: change in L/L initial L=Length

In regard to the musculoskeletal system, What are INTERNAL FORCES?

Note that when we talk about forces acting on the musculoskeletal system we often characterize them into forces coming from within the body called internal forces. Internal forces typically can be consider as active or passive in nature but they are generated from within the body. Consider a contracting muscle as generating active forces pulling on bone segments whereas internal passive forces can come from the tension of stretched tendons, joint capsules and ligaments on bone

Describe what you notice in the graph illustrating WHOLE MUSCLE LENGTH-TENSION RELATIONSHIPS

Note the separation of the active tensile force generated from its contractile elements and the tensile forces generated by the deformation (lengthening) of its in series and in-parallel components. Note that the total tension force generated by a muscle tendon unit increases with length greater than its resting length and decreases when the muscle is shortened below its resting length. This concept is extremely important to understand for Physical Therapists when designing interventions to improve a muscle's ability to stabilize posture or create a torque across a joint.

Compare OSTEOKINEMATIC and ARTHROKINEMATIC movement (without reference to forces)

OSTEOKINEMATIC Visible movement of bone around a joint axis relative to (X, Y, Z planes) i.e. gross movements of bones at joints examples: flexion, abduction These movements are under direct voluntary control ARTHROKINEMATIC Movements of joint articulating surfaces i.e. translation (glide, slide) of one joint surface on another, rotation of one joint surface on another, spin of one joint surface on another, or combinations of rotation and slide, (curvilinear) of one joint surface on another These movements are NOT under direct voluntary control

What can be observed about ECCENTRIC contraction on the FORCE-VELOCITY curve?

Observe here on the plot of isometric, concentric and eccentric activity vs velocity that during eccentric activity, force increases and is greater than both isometric and concentric contractions but eventually plateaus. Secondly, this graph reveals that force actually increases with faster velocity of lengthening. For therapists this suggests that individuals can generate greater forces during eccentric activity than they can during shortening or isometric contractions.

Muscle forces on bones are always _____________________ forces

PULLING

Will mechanical loads applied to ligaments and tendons only be applied to these tissues?

Physical Therapists should also understand that the mechanical loads applied to these tissues, as with nearly all tissues in the human body, will impart stress and strains not only to the extracellular components such as collagen, elastin, or proteoglycans, but also to the cellular structures within the tissue. Cellular structures under mechanical loads are in part responsive to these, converting these forces into chemical signals through a process known as MECHANOTRANSDUCTION. We all realize the effects of prolonged exercise training on muscles. Certain cells with muscles convert the mechanical loads they experience into chemical signals which give rise to increased protein production and making the muscle larger and stronger. Connective tissue cells such as fibroblasts and tenocytes are mechanosensitive and respond to external loads applied to them.

What is going on physiologically with OSTEOARTHRITIS?

REMEMBER-The flow of fluid in and out of cartilage can be described as its permeability. Higher permeability equates to faster deformation and lower permeability relates to greater stiffness. Osteoarthrosis is associated with cartilage demonstrating disorganization of its matrix with collagen degeneration and less proteoglycan levels. The consequence is greater and faster strain levels leading to further degeneration and thus a vicious cycle is seen where even physiological loads become destructive to the remaining cartilage.

Define COM/COG

Remember that the COG of a rigid object is the single point associated with a body/object where all of its mass is assumed to be located. It is a point associated with the object in which we can pretend that its entire mass exists at that particular point. NOTE: The key for therapists is to understand that this single point represents how the object's mass will behave when forces are applied to it. You will see in this week's lab that with most of the human body the distribution of mass is not constant and the COG location will shift to the direction of greater mass. Move your arms overhead while standing........your center of gravity for you whole body moves upwards.

we see that maximal force clearly decreases with increasing shortening velocity. How would increasing contraction velocity reduce the maximal force that could be generated by the muscle tendon unit.

Remember the cross bridges! In brief, cross bridges can attach and detach only so fast. When the actin-myosin filaments are sliding past each other in the sarcomere faster and faster there becomes less and less time for cross bridges to form and therefore the ability for tension in the sarcomere to develop decreases. Slow down the sliding of the filaments and more time is available for cross bridges to attach. For therapists, this would suggest that if an exercise intervention is given using concentric muscle activation, slower contractions will potentially allow the muscle's sarcomeres to generate more shortening force. This of course is not considering how the nervous system stimulates the muscle, but it should be understood that mechanically increasing shortening velocities potentially lowers the maximal force a muscle can actively generate.

Compare the mechanics of people on seesaws to the lever system in the body.

Remember the mechanics will be the same but instead of fulcrums we will be discussing anatomical joints, instead of boards of a seesaw we will be bones as the lever system, and forces will involve the intrinsic muscle forces and the external forces from gravity.

How do we quantify amplitude of EMG?

Root mean square

Similar to internal forces, external forces can create ____________ and ______________forces across limbs.

Rotational and parallel

Define ARTHROKINEMATIC ROLLING

Rotational movements of bone can also involved rolling motions. When a round object, like a car tire rolls, it travels forward on the surface of the road. What is observed is a combination of rotation and translation. To describe rolling we can define it by stating that in regards to the joint surfaces a series of new contact points on one articulating surface are coming into contact with a series of new contact points on another surface. During rolling the mechanical axis for rotation is changing its position. Contrast this to arthokinematic spinning in which the mechanical axis is stationary. Rolling of one joint surface on another during normal human movement is very minimal. When excessive rolling is seen to occur it may suggest joint dysfunction or injury.

If the osteokinematic rotatory motion is not occurring around a fixed mechanical axis then the motion is considered a

SWING Note: All other osteokinematic movements of a bone at a joint that are not spins are therefore swings. Swings refer to angular movements of the longitudinal axis of the moving bone when the mechanical axis is not fixed to one location only.

The in-series elements (SE) are composed of__________________, the parallel elastic components are composed of_________, and the contractile elements are composed of________________.

SE= tendons, CE= sarcomeres, PE: epimysium, perimysium, and endomysium

Forces applied parallel to a particular connective tissue's surface will be labeled as

SHEARING LOADS

You have learned that to lower the potential for reaching the point where ligaments or tendons begin to demonstrate permanent changes you should employ stretching techniques that are _________ and ______________.

SLOW and PROLONGED

What are the phases of ARTICULAR CARTILAGE?

SOLID PHASE: One phase is related to the resistance against deformation provided by its collagen network and the water content and termed the solid mechanical phase FLUID PHASE: the second phase incorporates the flow of water within and through this matrix which is described as its fluid phase. Note: Compressive loading will attempt to distort the cartilage and this results in tensile strains resisted by the Type II collagen fibrils within the cartilage. Additionally since water is incompressible when contained against flow, resistance to compression is also provided by the level of water contained in the cartilage itself.

Compare SPIN and SWING of bone.

SPIN is rotation around a fixed axis SWING is rotation that does not occur against a fixed axis

Explain when ACTIVE FORCE GENERATION (SARCOMERE) is greatest and least?

Sarcomeres appear to actively generate contractile tension in the middle of the range. Excessively short or excessively long will limit tensile force generation. But active generation is only part of the story.

Differentiate btw SCALAR and VECTOR quantities.

Scalar quantities refer to magnitudes only such as length, weight, and time. Vectors add orientation to a scalar quantity. Thus vectors have both magnitude and orientation Typically vectors are drawn as arrows to depict their direction as seen in the figure here. Vectors can be described by their orientations in the horizontal and vertical directions.

Compare fast/slow concentric and fast/slow eccentric movements

Slow concentric= less motor units recruited Fast concentric= more motor units Slow eccentric= more motor units recruited Fast eccentric= less motor units recruited Thus, muscles are more efficient with slow concentric and fast eccentric

What is the bandwidth for slow twitch motor units and fast twitch motor units?

Slow twitch motor units (tonic - Type I) Bandwidth = 20 - 125 Hz Fast twitch motor units (phasic - Type II) Bandwidth = 126 - 250 Hz

Define LINEAR STABILITY

So far we have discussed equilibrium and stability in more general terms but now it is necessary to be more specific so that we can relate these to some practical situations. Let's take stability and now characterize it further in terms of either linear or rotatory. Linear stability is the resistance of a body to having its linear equilibrium disrupted. In other words an object or a body is very stable against external forces that attempt to translate it. Mechanically how can an object provide more resistance to a change in its linear equilibrium state? One way is to manipulate its mass. Well if F = mass x acceleration then an object with a large amount of mass will require a large force to accelerate it. A football offensive lineman of 350 lbs is going to be a lot more resistant to changes in linear movement than one who is 250 lbs.

In summary, how does ARTICULAR CARTILAGE resist compressive loads from joint reaction forces?

So in summary, the ability for articular cartilage to resist the compressive loads from joint reaction forces can be attributed to its ability to attract and hold onto large volumes of water within itself. Water is incompressible and therefore the greater the volume of water the greater the resistance to compressive loads. Water flow in and out of cartilage effects compressive stiffness. Additionally cartilage expansion during an influx of water is resisted by its internal collagen framework which also provides an internal resistance to external compressive loads.

Hw do you calculate ANGULAR ACCELERATION of a RIGID BODY?

So to describe a body's motion during angular movements, similar to linear motion we often need to know whether the body's angular motion is speeding up or slowing down when rotating in a specific direction. To calculate acceleration (alpha) take the change in velocity of a body over a period of time and divide it by the length of time.

What are the types of JOINT MOTIONS (movement of joint surfaces relative to each other)?

Spin Roll Glide or slide Compression Distraction

Compare the mechanical axis of ARTHROKINEMATIC SPINNING and ARTHROKINEMATIC ROLLING.

Spinning: Mechanical axis is fixed Rolling: Mechanical axis changes position

When do SPINS of bone occur?

Spins of bone occur as rotations around a fixed mechanical axis. In other words if the bone moves and the axis remains stationary, then we describe this motion as spinning. bones like the humerus and femur are not simply straight bones but have an offset relationship of the head of the bone to the shaft of the bone. Here the hypothetical mechanical axis runs through the neck of the bone and through the center of the head of the bone and the bone spins around this stationary axis.

Muscles create ____________ and __________________ forces around joints.

Stabilizing and rotational

The parallel component is also called______________________.

Stabilizing component

What are the steps to creating a FREE BODY DIAGRAM?

Step 1: Identify and isolate the system of relevant rigid bodies -Draw a simplified figure to represent the body Step 2: Establish a sensible frame of reference using a coordinate system -Establish the orientation of the coordinate system Step 3: Sketch the internal and external forces acting on the rigid bodies -Sketch the vectors and points of application Step 4: Sketch the joint reaction force vectors Step 5: Create the appropriate mathematical equations related to analyses of each force.

What is STRAIN?

Strain: The percentage deformation, (shape, length, or width), of a tissue.

Differentiate between STRESS and STRAIN

Stress is the load and strain is the amount of deformation.

What is stress?

Stress: The internal reaction (resistance) of a tissue to an applied external force. More info: Thus the external force creating a deformation in the body gives rise to an internal resistance within the body. This internal resistance of a body, is termed stress. Note: The internal rejections and attractions and hence the resistance to deformation are related to the area of the force on the body. Stress is therefore standardized or normalized to the magnitude of the area and therefore it has the same units as pressure: force divided by area. Stress can be thought of as the internal resistance per unit of area to deformation from a force.

Describe the forces acting on a tendon.

Tensile forces on a tendon, such as the act of stretching a tendon, gives rise to internal tensile stress within the tendon itself Compressive forces on a tendon causes internal compressive stress within the tendon Shearing forces on a tendon gives rise to shearing stresses within the tendon.

In summary, the development of tension or tensile forces within a muscle tendon unit and the ability for a muscle tendon unit to elongate involves a complex relationship between its

active and passive elements

WHY WOULD LIGAMENTS, CAPSULES, & TENDONS BECOME STIFFER AS STRAIN INCREASES?

The answer lies to a large part on the molecular structure and orientation of its macromolecules, especially collagen. Collagen molecules are aligned for the most part in the long axis direction of the ligament or tendon. As the tissue is stretched, more of the fibers are directly aligned to resist the stretch and pack together which results in greater internal resistance as the tissue deforms more and more. Notice in the picture, as more external force is applied the internal resistance is generated from the fibers lengthening out.

Define BCOM

The body's Center of Mass (BCOM) is the unique point in space where the weighted relative position of each part of the body's mass lies. In simple terms it is the location at which the entire weight of a body may be considered as concentrated. When we are standing up vertically without moving about, your BCOM would be typically located at a point just anterior to your S2 vertebra. Often times the BCOM is called the COG and we can use either term as they essentially are the same thing. While in standing the BCOM is located roughly in the same area for most individuals, however the position of the BCOM is not fixed to that location. As we will see in this week's lab activities, the BCOM is calculated from the mass each part of the body, so if you raise your arm over your head the COG location moves upwards a bit. If a person is wearing a cast of their leg, the COG moves downward and slightly towards the casted limb. Note in the sketch here of an individual rising from a chair to standing, the location of the BCOM changes location from being quite forward at the onset of standing to just in front of the sacrum once fully erect.

View the graph on collagen production/organization and tensile strength

The graph depicted here provides a general overview of the relationship between collagen production and collagen reorganization verses tensile strength. On the Y axis is strength and along the X axis is the days following injury. Note, again that collagen synthesis increases significantly in the first 3 weeks. The increases in strength of the repair after day 21 are largely occurring as a result of collagen fibril reorganization along the lines of the long axis of the tendon or ligament.

How is base of support related to posture and balance?

The human's base of support is defined by the area bounded by a line surrounding the two feet laterally posteriorly to anteriorly. Consider where the COG vector should lie during standing so that we can related posture to balance mechanically. To stand and not lose your balance you must maintain the ability to control the center of gravity within the base of support in any environment.

Describe the 2 general effects a force exerts on a body.

The internal effect; which is the tendency to deform the body. The external effect; which is the tendency to initiate motion, change the motion of the body, or to develop resisting forces in the body

What is CENTER OF MASS?

The location (point) at which all of the system's (object's) mass is concentrated

Changes in the posture of one region can and will_________________________.

The main point to understand is that changes in the posture of one region can and will alter the posture in other regions and cause increased or sometimes decreased demands of the musculoskeletal system Note: While these individuals can adapt physiologically during quiet standing, the kinetics and kinematics of these regions change. In conditions where postural changes are more severe and prolonged, undesirable compensations can occur placing greater stresses and strains on the associated muscles, ligaments, bones, tendons, and joint structures.

What are the effects of AGE on CONNECTIVE TISSUE MECHANICAL PROPERTIES?

The properties of connective tissues in the musculoskeletal system change significantly after the age of 30. The graph here adapted from Yamada (1970) depicts the overall decline in tissue properties of elasticity, strength, toughness, resilience, and brittleness discussed earlier. While all mechanical properties are seen to decline with age, take note of the rapid decline in CARTILAGE properties during the third decade of life. As we will see, this is especially concerning because much of articular cartilage is aneural and avascular. Aneural refers to the lack of sensory feedback to loading conditions and avascular denotes limited vascular supply which in turn limits robust metabolism for repair when cartilage is injured.

What is a limitation of using EMG?

The recorded electrical activity of muscles under dynamic conditions does not show as strong a relationship with force production. This limits the usefulness of using EMG activation patterns to directly predict force generation of a muscle.

The ground reaction forces in the following image come through which space?

The red arrows represent the changing ground reaction vectors magnitude and orientation as the individual purposefully shifts from side to side and front to back. Remember that the origin spatially of the ground reaction vectors are through the individual centers of pressure of each limb.

Define resultant

The resultant is a representative force which has the same effect on the body as the group of forces it replaces. E.g. the resultant is the sum of the forces.

What does the SOMATOSENSORY SYSTEM offer BALANCE and POSTURE?

The somatosensory system is the network of sensors that provide specific feedback to the positions and motions of each body segment as well as feedback from interactions with the environment

Give an example of the internal forces needed to counteract external loads that effect the equilibrium of quiet standing.

The strategies using muscular forces to maintain posture are examples of the internal forces needed to counteract external loads that effect the equilibrium of quiet standing.

What is DEFORMATION STRESS-RELAXATION RESPONSE?

The tendency for a material held at CONSTANT LENGTH (CONSTANT STRAIN LEVEL) to experience a decreased magnitude of stress

What is DEFORMATION CREEP RESPONSE?

The tendency of a solid material to slowly deform (strain occurs) under the influence of a CONSTANT LOAD.

Define VELOCITY

The term velocity identifies and describes the rate of motion of a body and its direction. Speed is a scalar quantity, while velocity is a vector quantity and refers to the rate at which a body changes its position.

Longer fibers produce faster speeds; What type of fibers produce more force?

The two major structural determinants of a muscle's ability to generate active muscle force are: 1. The number of muscle fibers it possesses. 2. The architectural arrangement of its muscle fibers in terms of how the fibers line up with the tendon or the muscle's line of action during contraction.

What does the VESTIBULAR SYSTEM offer BALANCE and POSTURE

The vestibular system is your gyroscope which allows monitoring of linear and angular accelerations of your body in space.

Define ARTHROKINEMATIC TRANSLATION

The way we can define arthrokinematic translation is to state that sliding of one joint surface on another involves motion in which the point of contact on the moving surface is always the same but point of contact of the fixed object changes. For example, if the humeral head was sliding forwards on the glenoid fossa then the same general points of contact of the humeral head are meeting new points of contact on the glenoid fossa. Physical Therapists frequently use mobilization techniques to passively translate one joint surface on another to restore capsular or ligamentous extensibility when restricted. So, understanding the concept of translation arthrokinematically is very important to the therapist E.G. like going down a slide, the slide is fixed, so your body's contact with the slide is the same (your butt), but the fixed surface's (the side) contact with you changes

What are the 3 major sensory systems involved with posture and balance?

There are three major sensory systems involved with posture and balance are the vision, vestibular, and somatosensory.

Define STATIC equilibrium

This is the concept of static equilibrium which allows us to calculate the known and unknown forces acting on a body. When all the forces that act upon a body are balanced, then the body is said to be in a state of equilibrium.

Define Momentum.

Thus momentum is describing the mass of the ball in motion To describe this relationship of mass and velocity we use the term momentum. Momentum is the product of mass times velocity and quantifies the current state of motion and its resistance to changing that motion. The units for momentum are mass in terms of kilograms and velocity in terms of meters per sec, centimeters/sec etc.

What can we learn from EMG?

Time course of muscle contraction Level of activation Contraction force (if isometric) Fatigability of a muscle(s) Coordination of multiple muscles in a movement sequence These parameters are DERIVED from the amplitude, frequency, and changes of these over time!

Bone tissue has which components?

To begin with, consider that bone is a hard and rigid tissue of collagen, proteoglycan, and cells imbedded in a mineralized matrix. It's the inorganic components that make bone hard and rigid while the organic components give bone its resilience and flexibility Its mineralized matrix consists of inorganic salts including calcium carbonate and calcium phosphate along with small amount of inorganic sodium and magnesium. In addition to this, the matrix contains numerous collagenous fibers and a large amount of water.

How do you calculate the angular velocity of a rigid body?

To calculate the angular velocity, divide the change in the angle by the time it took during the angular movement from the initial position to the final position.

Given that gravity is always creating a flexion moment, what must the person do to resist the forces of gravity bending the spine even further into a greater thoracic kyphosis.

To stand vertically in static equilibrium..........there must be internal moments created by ligaments and muscles that resist these external moments. The main force comes from muscles that resist thoracic spine flexion; the thoracic spine paraspinals extensor muscle groups.

Here is another way to look at Torque

To visualize torque a different way observe the animation here of the man rotating the gear. To quantify the amount of torque the person is producing is simple math. Take the perpendicular distance from the line of action of the force to the axis and multiply this distance it by the magnitude of the pushing force he is producing at the edge of the gear. In biomechanics the term "moment" is often used to describe torque or the rotational force. The perpendicular distance from the force to the axis is termed the moment arm or torque arm. Finally, the units of torque involve Newton-meters, Newton-centimeters, etc.

Define TORQUE

Torque is the product of the force times its perpendicular distance from the center of the rotation or axis.

Define TOUGHNESS.

Toughness refers to the total energy absorbed by the tissue prior to failure Toughness has units of energy per volume and often represented as Joules/meter squared. The area under these stress strain curves represent the total energy absorbed by the material up until failure. The area under the curve can be quantified and a value of toughness for a material can be calculated. Here are two different materials, note that the areas under the curves are quite different with the left demonstrating a much high magnitude of toughness

True/False, forces that are parallel to each other, but act in the opposite direction and do not pass through the objects center of mass result in pure rotation, even if the axis is not fixed in space.

True

What are the units of force in biomechanics?

Typically when we attempt to quantify the size of a force in units of magnitude based on Newton's second law we will need to measure both the mass and the acceleration. The standard unit for mass is kilograms (kg) and the standard unit for acceleration is m/s2. So by convention a Newton is the amount of force required to accelerate a one kilogram mass 1 meter per second squared. 1N = 1 kg x 1m/s2.

How does COLLAGEN ELONGATE?

Ultra-structurally, collagenous fibers allow elongation via the reduction of the waviness of the bundles. (AS WE SAW IN TOE REGION ON STRESS STRAIN CURVE) Ultra-structurally, a small slipping of one fiber relative to the next one

In summary, what are the practical concepts for rotational stability?

Understand in practical terms, if the object's COG lays outside of the support base of the object it will topple over its edge due to the effects of gravity. Mechanically rotational stability can be increased if its COG is lowered or its COG is shifted more towards the side from which the unbalanced external force is applied as seen in the lower cartoon in this slide.

How do we calculate forces that are not in the same line?

Use resultant

What does VISION offer to BALANCE and POSTURE?

Vision allows feedback involving the immediate environment including planning of where steps are going to occur, where obstacles are positioned or as visual reference to what is vertical, far, or close.

Differentiate btw WEIGHT ARM and FORCE ARM

WEIGHT ARM= distance btw fulcrum and weight (resistance or external force) FORCE ARM = distance btw fulcrum and force (effort or internal arm)

What are the 3 components of a muscle tendon unit?

We can broadly model the muscle tendon unit as a 3 component model. The contractile components in this model are the sarcomere, the elastic components that are in-series with the contractile elements are the tendons, and the elastic components that run parallel to the sarcomeres are termed the in parallel components.

Define DYNAMIC EQUILIBRIUM

We can state that in the steady state of dynamic equilibrium all applied and inertial forces are in balance (net forces and torques = 0) which results in a body or object moving with unchanging speed or direction. Dynamic equilibrium is often confusing to grasp so for now consider it as a condition of "steady state" Dynamic equilibrium is a state when the sum of all vectorial forces are zero but the object still have a velocity. For now we will focus on static equilibrium both linear and rotation.

Why is it important for PTs to visualize/consider ARTICULAR CARTILAGE?

We cannot see it without special imaging tools Again it is relatively ANEURAL and AVASCULAR, therefore excessive loading is often not realized by patients Repair is often poor due to its limited blood supply. Therefore PTs should design interventions that support and protect against excessive external loading.

What are some clinical examples of when you would calculate torque?

We measure muscular strength by its ability to generate torques around our limb joints. Manual muscle testing and instruments specifically designed to measure torques such as the quadriceps and hamstrings during knee extension and knee flexion are used clinically to assess torque production by muscles. In principle the quadriceps torques are related directly to the same two variables; moment arm lengths and force magnitudes of the muscle. Biomechanically we can calculate the magnitudes of torques fairly simply as long as we know the variables

How do we define and quantify the mechanical strength of a connective tissue?

We simply use the stress strain relationship. Strength of a material is defined as the magnitude of stress or strain at which point the the material fails. For example, the Achilles tendon is frequently injured. How strong is the Achilles tendon in resisting an external tensile force? We can look at it from the point of strain or stress. Testing experimentally shows that the tendon can withstand up to 3500 newtons of external tensile force and can tolerate strains up to 12.5% before rupture. These are fairly impressive numbers

How do we quantify stiffness?

We use the slope (rise over run) of the stress-strain curve. Take y component (stress) and divide by x component (strain) This ratio of stress:strain Young's MODULUS helps us to visualize stiffness

How do you calculate weight?

Weight: = Mass x acceleration (gravity) Gravitational acceleration = 9.8m/sec2 (or 32ft./sec2)

Which type of muscle activity, isometric or concentric can generate the most amount of tensile force when fully stimulated?

You are correct! Isometric activity is occurring with zero contraction velocity thus, isometric activity can generate greater tensile forces compared to concentric activity

Describe CREEP of ARTICULAR CARTILAGE

When articular cartilage is subjected to rapid compressive forces such as with changes in weight bearing during ambulation, deformation develops instantaneously according to the tissue's stiffness property. This initial stage of rapid deformation demonstrates low matrix fluid flow, and the contour of the tissue changes but not its volume of water. The collagen fibrils and proteoglycans begin to realign and reorganize themselves as the tissue is initially deformed. The interstitial fluid pressure provides nearly 90% of the initial resistance to compressive deformation. As compressive loading continues a slower time dependent creep occurs related to the flow of water through the matrix. Over a period of 4 to 16 hours equilibrium between the compressive load and the interstitial pressure is achieve.

How do muscle move bones?

When attempting to understand how the contractile proteins of muscle cells provide forces to move bony segments requires further exploration of muscle tendon connections. The endomysium, perimysium, and epimysium are considered functional to lie PARALLEL to the contractile elements and thus are referred to as the PARALLEL ELASTIC COMPONENT of a muscle. They mechanically behave as elastic materials due to the primary element they are composed of---TYPE I COLLAGEN

More about LIGAMENTS

When we examine the mechanical behavior of ligaments, we find they are are strong, tough, and resist tensile deformation. During normal activity, ligaments are loaded in tension and elongate, allowing the joints to move easily and smoothly. During functional activities arising to greater joint motions, ligament stiffness restricts unwanted or excessive joint motions. Ligaments in the human body are not designed to prevent normal joint ranges of motion but to prevent unwanted translations between joint surfaces. In SUMMARY: Prevent unwanted translation between joint surfaces

Define WORK

When we start to define what a force does we are going to characterize work as the relationship between force and displacement. Work is therefore defined as the force required to move an object a certain distance.

Reduced loads can affect ARTICULAR CARTILAGE how?

While excessive loading may be detrimental to sustaining the necessary mechanical functions of articular cartilage: reduced or inadequate loading for prolonged periods may give rise to biochemical and mechanical changes which decrease the cartilage's ability to withstand normal physiological loads. Whereas prolonged increased loading results in increased GAG levels, decreased loading can result in reduced GAG numbers. Lower GAG levels means less water binding and decrease stiffness to compressive loads. Specialized magnetic resonance imaging techniques are beginning to illustrate GAG levels in articular cartilage. Less load = less GAG numbers/decreased stiffness to compressive loads

More about TENDONS

While tendon composition is relatively similar to ligaments, tendons present complex 3 dimension orientations. Collagen fibrils are oriented not only longitudinally but also transversely and horizontally. The longitudinal fibers run parallel but also cross each other, forming spirals. When we consider that the basic functions of the tendon are to both transmit and buffer some of the forces between muscle and bone the complex orientations of tendon fibers make this possible. Importantly tendon elasticity as noted earlier can be used as a mechanism for energy storage and release In SUMMARY: Tendons used to store and release energy AND to buffer forces between muscle and bone

Can you see or touch a force?

While you cannot see or touch a force we can visualize the changes in motion or the lack of changes between two bodies because of their interactions.

Can muscles store elastic energy?

Yes, Muscles and tendons can store and then return elastic energy during motion. In other words the elastic properties of the connective tissues of muscles and tendons can be force generators when needed. As we will see, the musculoskeletal system takes advantage of the stress strain relationships during movement and thus it is important for therapists to understand these basic material properties.

How do I solve LINEAR ACCELERATION OF A RIGID BODY?

a (alpha) is symbol for acceleration

What is one method to increase rotational stability?

another method to increase rotational stability is to lower the COG of the object because when the COG is vertically lowered, the object's COG must be rotationally displaced a greater distance to end up with its COG outside its support base. In other words lowering the COG will require greater torque to move its COG outside of its support base. This is why intuitively you have learned or have been taught to assume a lower stance when an external force is trying to topple you over. another method is...The pyramid resists being toppled over as long as it keeps its COG within its base of support. The closer the COG is to the location of the axis the less torque is needed by the man to rotate the pyramid clockwise. Once the COG passes the base of support it topples over

Define RESILIENCE

as the property of a tissue to absorb energy when it is elastically deformed and then, upon unloading to have this energy vigorously recovered Note: This tissue recovers its resting length or shape very quickly upon release of the external load e.g. the Achilles tendon during walking is an example of the properties of resilience. Apply a stretching load to the Achilles tendon to lengthen it and upon release of the stretching force the tendon vigorously returns back to its resting length. tendons in general have a high resilience

List examples of BIOLOGICAL CONNECTIVE TISSUES

bone, cartilage, muscle, nerve, ligament, tendon, menisci, or intervertebral discs are all subject to external forces.

How are CARTILAGE PROTEOGLYCANS important components in limiting excessive compressive loading during joint reactiopn forces?

by being hydrophilic, (high affinity for binding water), and polyanionic (meaning they possess many negative ionic charges) Note: Proteoglycan complexes lie primarily in the deeper layers of articular cartilage and consist of a protein core, (blue line) in which glycosoaminoglycans such as Keratan Sulfate and Chondrotin Sulfate attach in a bottle brush appearing type of arrangement. These protein cores in turn bind to the backbone of a large macromolecule called Hyaluronic Acid (green line).

If the line of action is _____________________ to the rigid body's center of mass it creates ______________ but the body will also _____________ unless the axis is ____________ (like a door hinge).

eccentric; rotation; translate; fixed

Any upright posture is a battle between the ______________________________.

force of gravity, center of gravity, base of support, and mass distribution of the body

Whenever we are attempting to analyze the effects of a force vector, as stated before, we always need to do so in relation to a _________________that is sensible to us.

frame of reference

Why is ELASTIN important?

gives tissues some of their elastic resilience Elastin is the final extracellular component of connective tissue important to Physical Therapists. Elastin is another important macromolecule that provides elastic properties to tendons, ligaments and other connective tissues. While collagen for example is still the main fibrillary component of the Achilles tendon, elastin is present at a significant level. Ligaments generally contain more elastin than tendons making them less stiff and just slightly weaker than tendons.

in simple terms muscles with larger physiological cross sectional areas generate more tensile force because they have

greater numbers of contractile proteins.

The more fibers that are stretched, the __________________________.

greater the length developed by the whole muscle.

zero net force or zero net torque acting on a object or body does not mean _____________________but does mean _______________________.

it is not moving ; that the object or body is NOT accelerating (no change in velocity).

How stiff a tendon or ligament is depends on...

its collagen arrangement and the interactions of the collagen with other collagen molecules or with interactions of collagen with other extra cellular components. Honey is more viscous then water. It has a higher resistance to flow, but if you heat honey it becomes less viscous; it has decreased its resistance to flow.

A muscle with a larger moment arm produces a ____________________torque than a muscle with a smaller moment arm if both muscles have equal contractile forces.

larger;

How do we calculate TORQUE?

math= the force x perpendicular distance from the center of rotation, (axis)

Destruction of either the proteoglycans or collagen significantly affects ARTICULAR CARTILAGE's ability to ____________ and can lead to___________________. Hoe does this relate to PT?

resist the normal joint reaction forces occurring with physical activity and can lead to its degeneration over time. Note: Often Physical Therapists provide interventions in which partial destruction of articular cartilage has already occurred and must be aware of how to prevent further degeneration by properly controlling the external loads arising from daily activities of living.

To describe torques you need to describe the direction of ______________________.

rotation; e.g. one boy is producing a clockwise torque and the other a counterclockwise torque. Thus, STATIC equilibrium

In which lever system is the force, effort, arm ALWAYS longer than the weight or resistance arm?

second class

Look at the picture on the next side. Which scenario will require greater muscle contractile force? Why?

see p. 95 textbook A. internal and external torque potentials are maximal as well as optimally matched B. Ext torque remais the same but angle of insertion changes and thus requires more contractile force to produce the same internal force.

Clinical Application: To increase length of ligaments/tendons apply a ...However, if you want to permanently lengthen a tendon or ligament you would employ a technique that creates ________________________.

slow low load force for an extended period of time; plastic deformation.

Physical Therapists involved with stretching activities of tendons will find that they are more effective when the stretch position occurs

slowly and for a prolonged period to maximize creep and stress relaxation.

Clinical Application: Following injury or post surgical repair, ___________amounts of tensile forces stimulate fiber orientation and collagen production

small

Describe STATIC POSTURE

static posturing describes the alignment and orientation of an individual's trunk, neck, head, and limb segments with respect to three cardinal planes. Typically this most often involves angular measures from vertical such as when an individual is standing, sitting, or kneeling.

Again, what are the 3 components of a muscle tendon unit?

the 3 component model of the muscle tendon unit incorporating the parallel elastic components of a muscle, the active contractile units, and the in series elastic components which generally constitute the tendons structures. When a muscle actively shortens or a muscle lengthens effects on each of the components of this model can be appreciated. These three components, acting together help to regulate the tensile forces that are imparted to bony segments.

Define CENTER OF PRESSURE

the center of pressure, called the C.O.P., is merely the spatial location of the average of all contact pressures (collisions) between the plantar aspect of foot and the ground. We can measure each of the contract points and their individual pressures with special instruments. So as the body weight presses down against the ground we can take each and every one of the foot's contact points, measure the corresponding pressures at each point and then calculate the weighted average of all contact points. When we do this we arrive at a location which is the centroid of all of the individual pressures. This derived point is important because the location of the GRF's origin is generally through this point as we stand. A graphic representation of the pressures under the foot are seen here. Different colors represent different magnitudes of pressure. Note that when standing, the COP is located just in front of the ankle.

The TRANSMISSION OF TENSILE FORCES between muscle cell to tendon occurs as a result of

the shearing forces between the folds of the muscle cell's sarcolemma and the collagen fibrils of the tendon. More info: Imagine friction forces between overlapping collagen fibrils and the muscle cells sarcolemma which is reinforced in the folds by actin proteins. The collagen fibers and muscle cells literally interweave with each other and coupled with the extensive complex folding of the cell membranes forces are transferred between muscle cells to tendons. It is estimated that the folding increases the contact areas 10 to 20 times between the two tissues. For Physical Therapists, this folding often is disrupted and is not often fully restored after injury to the musculo-tendinous junction of a muscle. This potentially weakens the connection altering force transfer and increases the risk for secondary injuries

Define POINT OF APPLICATION

the specific location of where the force is applied to a body.

MECHANICAL ADVANTAGE allows a muscle to

to move a heavy object using less force than the weight of the object, allows a muscle to accelerate an object faster then the speed of its force production, and allows a muscle to move an object further than the distance applied to the lever itself.

When the line of action of a muscle is eccentric to a joint axis then the pulling force acts as a _____________________. If the line of action passes through a joint axis then the pulling force becomes a ________________ by compressing opposing joint forces together.

torque generator; stabilizing force;

The motions at joints include...

translations, rolls, and spins.