Biomechanics test 3

Interneurons

(CNS- type of neuron) -Interface with the sensory neurons, provide stimuli to motor neurons

Center of Mass

(COM) -Point around which the mass and weight of an object are balanced in all directions -Equally distributed in all directions -Can also be referred to as Center of Gravity (COG). It is a SINGLE POINT associated with a body where if supported at that point the object will remain balanced. COM doesn't have to be inside of that mass.

Pacinian Corpuscles

(Exteroceptors) -Change in joint position -Sensitive to changes in pressure

Cutaneous pain receptors

(Exteroceptors) -Withdrawl reflex

Stability

(How well you are maintaing that original position) Capacity of an object to return to original position (equilibrium) after it has been displaced. Give a perturbation and observe the new behavior. If new behavior= old, then the system is "stable" if new behavior doesn't= old, then the system is described as "unstable"

Physiological Cross Sectional Area

(PCSA) -Cross sectional area of muscle PERPENDICULAR to muscle fibers -Provides and indication of the maximum tensile force a muscle is capable of producing

Proprioceptive neuromuscular facilitation stretching

(PNF) -Quick stretching--> muscle contraction -Isometric contraction before stretching stimulates GTO and inhibits muscle contraction -Muscle more relaxed when stretching

Motor/efferent

(PNS- type of neuron) -Receive stimuli from interneurons or sensory neurons -Sends signal to muscles

Parallel elastic component

(Passive contributors to tension development) -Passive elasticity derived from muscle membranes -Supplies resistance when muscle is passively stretched

Series elastic component

(Passive contributors to tension development) -Plastic elastic properties of muscle derived from tendons -Acts as a spring to store elastic energy when a tensed muscle is stretched

Control of muscle force-summation

(aka rate of stimulation) -If 2nd action potential is received before tension of first has subsided, tension from the second twitch sums and so on... -We may not be able to to voluntarily recruit all of our motor units -Electrical stimulation

Purpose of ligaments

(attach bone to bone) 1) Mechanical joint stability 2) Guide joint motion 3) Contribute to proprioception/position sense "restraints"

Ground substance

(biological tissue that makes up human tissue) carbohydrates and proteins combined with water. Forms gel like matrix for collagen.

Collagen

(biological tissue that makes up human tissue) most abundant connective tissue in body. Stiff with high tensile strength. Buckles under compression.

Elastin

(biological tissue that makes up human tissue) very pliant and extensive

Compression

(compressive stress) axial stress that results when a load tends to push or squash the molecules of a material more tightly together at the analysis plane. load pushes the material more tightly together. Object shortness in direction of the external forces.

Agonist

(concentric actions) muscle creates a torque in same direction as joint action -Biceps agonist for elbow flexion, triceps for elbow extension

Eccentric contraction

(control movement) -When a muscle is active and its attachments are drawn father apart -Torque created by active muscle in opposite direction to the limb rotation -Limbs velocity slows down OR it is being lowered -Flexor muscles are active but extension occurs -Extensor muscles are active but flexion occurs

Mass of an object

(factor affecting stability) -F=ma -The more massive an object is, the greater force that is required to produce a given acceleration

Friction

(factor affecting stability) -Greater the ________ between an object and surface, greater force to initiate and maintain motion

Internal perturbation example

(inside the body) any force within you that causes you to move (muscles, breathing)

Proprioceptors

(interoceptors) monitor status of musculoskeletal system

Stabilizer

(isometric action) that keeps a limb/bone from moving when a reference muscle attaches -Some of the muscles attaching to the scapula

External perturbation example

(outside the body) any object within the object that causes it to move (push or pull)

Cell body

(part of a neuron) contains cell nucleus and other metabolic structures

The axon

(part of a neuron) nerve fiber that conducts the action potentials

Dendrites

(part of a neuron) receives impulses from other cells and send to cell body

Trabecular or cancellous bone

(spongy bone) -Less compact/dense -High porosity -Ends of long bones, vertebrae

Factors affecting biochemical properties

-Age: strength, ability to withstand deformation -Pregnancy and postpartum period: increased laxity of tendons, ligaments, in pubic area during later stages of pregnancy -Mobilization/immobilization: increased strength/stiffness with mobility decreases with immobility11q

Diminishing bone density

-Aging -Lack of weight bearing exercise -Bed rest -Traveling in space outside the earth's gravitational field

Sarcomere

-Basic contractile unit of muscle -Actin and myosin (myofilaments) overlap within the sarcomere

Motor unit sizes

-Bigger muscle have more motor units -Innervation Ratio = # of motor units: # of muscle fibers Gastrocnemius= 1:1934 -580 motor units 1.12 million muscle fibers First Dorsal Interosseus= 1:342 -120 motor units to 41,000 muscle fibers

COM and the human body

-Body is not rigid object -COM is dependent on limb position

Bone strength

-Bone is strongest in compression -Bone is weakest when bone is acting perpendicular to the bone and somewhere in between for tension

Activity and aging

-Connective tissue strength increases with regular cycles of loading and unloading. -Typically due to cross sectional area increase -Can also independently increase strength -Immobilization/inactivity= decreases strength Tissue have increase in ultimate strength until the 3rd decade of life, after this it decreases and bones become more brittle; less tough. Tendons and ligaments become more stiff.

Control of muscle force-recruitment

-Control the number of active motor units -Small/low force= small number recruited

Tensile force vs. elongation of a rubber band

-Elastic: stretches under load and returns to original position when removed. -Different materials have different properties

The motor unit

-Fundamental unit of the neuromuscular system -Single motor neuron and all the fibers it innervates -All-or-nothing principle: all muscle fibers in an individual motor unit contract together

Golgi tendon organs

-Located in tendon (in series with the muscle) -Stimulated by tension in tendon -Stretching -Muscle contraction Inhibitory effect -Contraction inhibited

Series arrangement of myofibrils

-Longer muscles can stretch and shorten over greater lengths that shorter muscles -Muscle is not stronger even though it contains more myofilaments -Does weight training result in larger muscles?

Contraction mechanics

-Motor neuron stimulates muscle -Muscle becomes active -Cross bridges of myosin attach, pull, release to actin -Force is the sum of all pulling forces of myosin on actin

Function of skeletal muscle

-Movement -Posture maintenance -Heat production -Shock absorption -Protection

Flexibility exercises

-Muscle stretched effectively when relaxed -Quick stretch= contraction -Slow stretch= small reflex response

Force generation

-Muscles always pull -Pull equally on both attachment sites -Force represented by line of pull

Muscle length-active tension

-Optimal length= max tension -Overlap beikikkm tween A & M is maximal -Less than optimal= less tension (too much overlap between A & M) -Longer than optimal= less tension (only a few A & M can attach)

Composition of tendons

-Parallel fibered collagenous network -Type 1 collagen -Sustain large tensile loads -Allow for some compliance/deformation -Elastin: 2% of the dry weight

Factors that influence muscle contraction force

-Physiological cross-sectional area -Muscle length -Contraction velocity -Muscular torque influenced by each of these factors plus the size of the muscle moment arm

Plastic behavior

-Plastic: permanent deformation of the object occurs -Below proportional limit: material behaves elastically Above proportional limit: material behaves plastically

Tendon reflex

-Protects muscle from rupturing/tearing by turning off the active development of tension if tensile forces are too great -Joint collapses under you during take off for a jump -Strong muscle contraction=relaxing of muscle

Mechanical properties of bone

-Rate of loading matters! -Stronger when load applied more quickly than slowly -Avulsion fraction vs. ligament tear -Avulsion: ligament pulls out of attachment site

Exteroceptors

-Respond to stimuli external to the body -Sight, hearing, touch and pain

Uses of COM

-Serves as an index of total body motion -Body responses to external forces though all masses concentrated at the COM -Point at which vector acts of a FBD -Fluctuate up and down when running -Moments are balanced on either side of the COM -You can have equal moments on either side with UNEQUAL weights

Other factors that affect the maximum force of active muscle

-Temperature -Pre-stretching muscle just before concentric contraction =Fatigue =Fiber type

Influence of age in osteoporosis

-Traberculae lose thickness -Some transverse traberculae dissapear

Composition of ligaments

-Type 1 collagen fibers that are not completely parallel -Bear tensile loads in long direction -Can bear smaller tensile loads in other directions

Isometric contraction

-When a muscle is active and its attachments do not move relative to each other -Holding a position or resting against an external force

Concetric actions

-When a muscle is active and its attachments draw closer together -Torque production in same direction as limb rotation -Limb velocity speeds up or limb is being elevated -When a flexor muscle is active and flexion occurs -When an extensor muscle is active and extension occurs

Purpose of tendons

1) Attach muscle to bones 2) Transmit tensile load from muscle to bone to produce joint stability or motion 3) Provide mechanical pulleys 4) Motor control

Characteristics that influence moment production

1) Muscle architectures, 2) muscle length at contraction 3) contraction velocity 4) muscle moment arm length

Balance

A person's ability to maintain COM/COG within their base of support

Microstructure of skeletal muscles

A single muscle cell is a muscle fiber. Covering the muscle fiber is a thin cell mebrane called the sarcolemma. External to the sarcolemma is the endomysium, the connective tissue sheath that encases each muscle fiber and anchors it to other muscle fibers and connective tissue and eventually to the tendon. Within each muscle fiber are hundreds of smaller threadlike structures lying parallel to each other and running the full length of the fiber. These are the myofibrils. The region that includes only actin filaments and the Z band is called the I band and appears as a light band. The darker band or region that includes the full length of the myosin filaments along with the region of overlap with the actin filaments is called the A band. The region within the A band where the actin and myosin do not overlap is called the H band or H zone. At the middle of the H band is the M band or M line, the transverse band that connects adjacent myosin filaments with each other.

Toughness

Ability of material to absorb energy. Area under stress strain curve

Distinguishing characteristics of a muscle

Ability to actively shorten and develop tension

Prolonged injury

An injury that occurs over a long period of time (construction workers example)

Mechanism of overuse injury

An overuse injury: can occur following repeated applications of a stress lower than that required to cause injury in a single application. The higher the magnitude of stress imposed, the fewer repetitions needed for an injury to develop. It appears that what determines whether imposed stress will cause a training effect or lead to an injury is the amount of time provided for remodeling to occur. If the stress is reimposed but adequate time for the tissue to repair is not provided, an overuse injury eventually develops. W/o adequate recovery time, stress is imposed on tissue that is already damaged, and the repetitive loading increases the extent of damage.

Stiff

Applying a large load causes a small deformation

Pliant

Applying a small load cause a large strain

Base of support

Area beneath and between the points of contact a person has with the ground

Base of support (factor affecting stability)

Area bound by the outermost region of the body and support surface or surfaces. -Must keep line of action of the COG WITHIN this to stand upright (when a line of action moves outside the base of support, you fall). -To increase stability increase the size of the _____ __ ________ in direction of external force -Position COG near edge of ______ __ _______ on the side of the external force -Even when you are just standing, you are always moving

Wolff's law in bone

Bone strength increases and decreases the functional forces on the bone increase and decrease. Increases and decreases strength in direction force is applied

Elements of the nervous system

CNS (brain and spinal cord), PNS (12 cranial nerves, 31 pairs of spinal nerves). Fundamental unit of this system is the nerve cell.

Application of COM to performance

COM path during takeoff events (high jump) believed to distinguish skilled from non-skilled athletes Why is it important? -Strategy is to lower COM prior to take off -Lengthens vertical path that the COM is accelerated -Facilitates higher take off velocity -Total body COM is a weighted average of segments that make up the limb

Intrinsic factors

Characteristics of the individual. They generally reflect an individual's ability to withstand loading. _______ ______ related to injury include anthropometrics; skeletal structure, such as bone density, and joint congruity (alignment); current fitness level, such as muscle strength, endurance, and flexibility; and previous history of injury.

Extrinsic factors

Characteristics of the task and the environment in which it is performed. Task-related factors include the nature of the task being performed; how a given individual performs the task; the movement of patters involved; and the frequency, speed, and duration of performance. Environmental factors include the type of surface played on, the rules used, the skill level and number of teammates and opponents, the type and condition of protective equipment , the type and condition of implements, and the current weather conditions.

Contraction velocity

Concentric/shortening velocities: -Crossbridge cycle: attach--> pull--> release -When XB in release doesn't contribute to tnesion -Slower= less XB in release -Faster= more XB in release Eccentric contractions/lengthening: -Controlled lowering of an object -Energy released from XB as they are broken -Force of contraction: eccentric-->isometric-->concentric

Two joints musculature

Crosses 2 joints (gastrocnemius, long head of biceps)

Multi-joint

Crosses more than 2 joints (muscles of the fingers)

Cell membrane of a neuron is excitable

Depending stimulus it can be: -Excitatory -Inhibitory -If there is an increase in membrane potential, an action potential is generated -AP propagates along the membrane away from cell body

Brittle

Does not have a plastic region. Dry bone, chalk

How are external forces and internal forces related

External force-->internal force--> injury. Forces acting on a body are responsible for the occurrence of an injury. An injury us damage to a tissue that inhibits performance. "High levels of force" cause injury. More than force magnitude and direction are responsible for injury. Mechanical stress (pressure) refers to the distribution of force over the body that it acts on.

Stress

External forces resisted by internal forces and cause deformations to the body. May vary within an object and is associated with a specific internal surface. Amount of deformation related to STRESS. Stress: internal force/cross sectional area of internal surface. Units: N/m^2

Force

External forces-->internal forces-->injury

Force production

For this, we need attachment of the cross bridges of actin and myosin. Force developed in sarcomere proportional to number of cross bridges.

3 biomechanical factors related to injury

Force, posture and repetition

Muscle spindles

Give feedback on increased muscle length -Stretch of muscle -Relative changes in length Stretch muscle= stretch spindle -Sends signal to motor neuron to reset tension in the muscle fibers

Other factors affecting stability

Height of the COM relative to the base of support -Need to vertically position the center of gravity as low as possible -Related to potential energy

Longitudinal vs. pennate muscles

Human muscle can produce a tensile force or approximately 30 N/cm^2 of cross-sectional area of active muscle during an isometric contraction. Thus a longitudinal muscle with a diameter of 3 cm can produce a maximal isometric contraction of 210 N. The minimum contraction length of a longitudinal muscle is shorter that that of a pennate muscle if their resting lengths are the same. The longitudinal muscle can create tension through a greater range.

COG

Imaginary point at which the entire weight of the body may be assumed to be concentrated -Also referred to as the point of balance

Parallel arrangement of fibers

Increasing the # of muscle fibers parallel to each other increases strength of the muscle.

Factors are not independent

Max tensile force depends on both length of a muscle and velocity of shortening/lengthening

Relationship between contraction velocity and tension

Maximum eccentric activity is stronger than maximum isometric activity, which is stronger than maximum concentric activity

Ultimate strength

Maximum stress tissue capable of withstanding

Ductile

More maleable, larger plastic region. Soft candy

Macrostructure of the skeletal muscles

Muscle fibers are bundles together in groups of 100 or more to form a fascicle. Each fascicle is encased by a connective tissue sheath called the perimysium. The endomysium of each muscle fiber is bound to the perimysium. Several fascicles are then bound together within a connective tissue sheath called the epimysium to form a whole muscle. The force of a muscular contraction is thus transmitted from the endomysium of the muscle fiber to the perimysium and epimysium and the to the tendon, which is a continuation of these connective tissues.

Avulsion fractures

Occurs when high tensile stress in a tendon or ligament breaks off bone at the site of attachment, are more likely when muscle activity is high or when a joint is pulled to an extreme end of its range of motion.

Tension

One of the 2 axial stresses, and one of the 3 principal stresses. Axial or normal stress that occurs at the analysis plane as a result of a force or load that tends to pull apart the molecules bonding the object together at that plane. Acts perpendicular or normal to the analysis plane and is thus called a normal stress or axial stress. When force is applied that tends to pull apart a tissue/object. When loaded in tension, object will deform by stretching or elongating in the direction of the applied load.

Sensory/afferent

PNS (Type of neuron) -Responsible for sensations -Receive info from internal/external environment and send back to CNS

Osteoporosis

Pain; one or more fractures resulting from activities of daily living. -Type 1 (post menopausal): affects- 40% of women>50 years -Type II (age associated): most women and men after age 70 Bone porosity primarily determines a bone strength

Strain

Quantification of the deformation of a material (changes in objects length). Produced by tensile or compressive stress. Strain= change in length/original length= 5mm/10mm= 0.5 mm/mm= 50% strain. Linear ______ is produced by compressive or tensile stresses. Shear strain occurs as a result of a change in the orientation of the object's molecules.

Elastic modulus/stiffness

Slope of a stress strain curve. The more steep the curve, the stiffer the material. Ratio of stress to strain.

Failure strength

Stress where failure actually occurs. Failure= complete fear

Stretch vs. Tendon reflex

Stretch reflex operates as feedback mechanism to control length by causing contraction. Tendon reflex operates as feedback mechanism to control muscle tension by causing relaxation before injury occurs.

Bone

Strongest and stiffest material in the body. 30-35% collagen, 45% minerals and 20% water.

Stretch reflex

Synapse occurs between sensory and motor neurons-->contraction -Stretch quick= strong contraction -Falling asleep in class -Eccentric contractions of stretching muscles to slow down limbs

External-->Internal forces

The external forces that act on the body impose loads that affect the internal structures of the body. Bones break, ligaments tear, muscle pull. Loads applied exceed the tissue strength.

Stress-strain relationship of an elastic material

The more you stretch it, the greater the force you have to pull with. Because the rubber band was stretched by a uniaxial load, the stress and strain in the rubber band are uniform. Rubber is elastic (vs. plastic). It stretches under a tensile load but returns to its original shape when the load is removed. This property is called elasticity. Rubber is linearly elastic because, as the stress increases, the strain increases a proportional amount. The ratio of stress to strain is called elastic modulus of a material. A material that is more stiff has a steeper slope of its stress-strain curve, and thus a larger elastic modulus, than a material that is more pliant.

Walking

There are times when you want to be unstable. To walk you must shift support from one foot to the other foot. Move COM outside initial base of support of your "stance limb" in the direction you want to go. React by creating a new support base of support (baby crawling, firefighters)

Internal moment=reaction moment

This is the amount of force that must be produced to be able to resist moment created by the weight of forearm+hand and resistance. This is NOT how much force the individual can produce.

Passive insufficiency

Unable to reach full range of motion because of the limit of muscle length

Active insufficiency

Unable to reach the contraction force because of the limit in muscle length

Bone response to stress

Weight bearing exercises: -Larger the forces acting on the skeletal system, greater bone development Recommendations from the National Institute of Osteoporosis and Related Bone Diseases recommends that people: -walk -hike -jog -climb stairs -lift weights -play tennis -dance

Mechanical strength and failure

What is the maximum stress (or strain) the material is able to withstand before failure

Model for overuse injuries

William's model for the effect of repetitive stress imposed on the body. The imposed stress causes microscopic tissue damage and initiates tissue remodeling. If the rate of remodeling is greater that the rate of tissue damage, a training effect occurs and the the tissue gets stronger. if the rate of remodeling is slower than the rate of tissue damage, an overuse on injury develops.

Neutralizer

creates a torque to oppose an undesired action of another muscle

Single joint musculature

cross one joint only (soleus, short head of biceps)

Stress continuum

demonstrates that the level of stress imposed on a body ranges from low (pathologic underload zone) to high (pathologic overload zone). Undesirable effects occur when the level of imposed stress is too low or too high. A training effect occurs if the level of stress is systemically raised above the physiologic loading zone, or the level of stress to which the body has adapted.

Repetitive/overuse injury

described as tissue damage that results from repetitive demand over the course of time (man moving boxes)

Cortical bone

found in the dense and hard outer layers of bone (surrounds the bone). -Compact -Low porosity -Shaft of long bones

Anisotropic materials

have different mechanical properties depending on the direction of the load (biological tissue/connective tissue)

Isotropic materials

have the same mechanical properties in every direction (synthetic materials)

Reflex

involuntary responses from sensory input and little (if any) input from CNS

Antagonist

muscle creates torque in opposite direction of joint action -Biceps antagonist to triceps/elbow extension

Interoceptors

respond to stimuli from sources internal to the body

Wolff's law

states that a tissue adapts to the level of stress imposed on it; that is, the level of adaptation in a tissue reflects the level of typical loading. If the level of imposed stress is not raised out of the underload zone, a detraining effect occurs.

Yield strength

stress at the elastic limit. NO breakage of material occurs, but permanent damage occurs beyond this point. Severe strain of a ligament w/o tear.

Acute injury

sudden injury that is usually associated with a traumatic event such as clashing into another player during sports or a fall from a bike. You body undergo changes during this period and often it is a negative one. A traumatic impact can cause your bone to crack, muscles to tear or ligaments to snap (Guy on a jet ski)