Kinesiology Lecture 3: Biomechanics

Levers

EARS ARE AER-odynamic!

Application of Linear Forces

Forces along the SAME LINE with "roughly" same point of application Pulling in one direction pushing in the same direction = linear force system

Active motion

Motion which is generated by muscle contraction, in which the person is moving a joint with the associated muscles - individual moving joint with associated muscles.

Concurrent Force System

Two or more forces acting upon an object at a common point, but in divergent directions Not too typical for muscles, but two examples Deltoid - point out anterior (shoulder flexion), posterior (shoulder extension), and middle (abduction) Overhead: clavicular portion of pec major and sternal portion have common attachment on humerus. When both contract simultaneously, the resultant force is horizontal adduction

Force Couple

Two or more forces acting in equal, but different directions resulting in a turning effect Two hands turning a steering wheel: right hand pulling down (click) and left hand pulling up (click)...and it still turns the wheel to the right... We will return to this concept later - but for now an example would be Example in the body: scapular upward rotation with UT, LT & serratus anterior working together as a force couple...more on that later...

Center of Gravity - that part of the body about which all the parts exactly balance one another CENTER OF GRAVITY... •that part of our body about which all the parts exactly balance one another...the point of the body at which the entire weight of the body may be considered to be balanced.

Center of Gravity

Rectilinear

Rectilinear: straight line (arm moving forward on the table)...occurs in more or less a straight line from one location to another.

A.Convex member rolls and slides in opposite directions B.Roll but no slide....pain on the superior aspect of the joint!

Convex on Concave

Curvilinear

Curvilinear: curved line or hand to mouth to drink (movement occurs in a curved path that isn't necessarily circular)

Example

•Nutcracker (overhead) •Effort - hand squeezing •Resistance force - nut •Resistance arm - between nut and axis

Motion

●Motion is classified as active or passive

Forces

ALL forces can be described as a push or a pull of one object on another.

FIRST-CLASS LEVER: EXAMPLE

Ex: Supraspinatus (shoulder abduction)

True/False: Given equal forces, a second-class lever will have good mechanical advantage because the effort/force arm is longer than the resistance arm.

True

True/False: When a convex joint surface moves on a concave joint surface, the roll and slide occur in the opposite direction.

True

Which involves all parts of an object moving at the same time, in the same direction, but different distances?

rotary motion

Application of Concurrent Forces

Overhead: Two people pulling the boat - net effect or resultant action will be in a line that lies between the two resultant force is the diagonal of a polygon Overhead: deltoids - linear force with concurrent force system ant & post portion act on humerus to raise into AB

Parallel Force System

Parallel Force Systems: 2 or more parallel forces act on the same object in the same plane, and in the same or opposite direction. Example: abdominals and extensors on the trunk To evaluate the effects of forces on levers in the human body we need to analyze forces that have action lines that never converge. These Parallel systems most often seen in the body

What is the best description of an internal moment arm?

Perpendicular distance between the axis of rotation and the muscle's line of pull.

Analysis of Levers

Remember: "Leverage" help us gain some kind of advantage (such as greater force) Rigid bar that is being acted upon by parallel forces that cause it to move in a rotary motion. All levers have four components: 1. A rigid bar - bone in the body 2. An axis - fulcrum / point of rotation 3. Effort force (or force in some texts) 4. Resistance force Effort arm - distance between the effort force and the axis Resistance arm - distance between the resistance force and the axis _______________________________________________________ _____________________________________________________ We need to understand lever systems •To understand how the levers of the body moves •To understand how we do things •(MOVEMENT IN THE BODY IS A RESULT OF LEVERS!) NEXT SLIDE - EFFORT FORCE AND RESISTANCE FORCE.... OVERHEAD: LEVER COMPONENTS

Resistance Force

Resistance Force = that which is attempting to resist motion •Often difficult to determine which is the effort force and which is the resistance force •Effort force - Always the winner in the torque game •Resistance force - Always the loser in producing rotation of the segment •When there is equilibrium, the distinction is arbitrary... •Movement will cause rotation •will always occur in the direction exerted by the effort force •unless at equilibrium. EXAMPLE ABOVE HAS DIFFERENT AXIS POSITION compared TO OUR PREVIOUS SLIDE •Depending on where the forces are in relationship to the axis • levers can be classified into three classes

multiple points on one rotating articular surface contacting multiple points on another articulating surface

Roll

Rolling and gliding must couple together or that bone that is rolling will roll off! - The concave joint surface moves in the same direction as the body segment's motion - A convex joint surface will move on a fixed concave surface in the opposite direction as the moving body segment Hand in fist example for visual: Convex: rounded outward, much like a mound (fist) Concave: "caved" in much like a cave (letter C)

Roll and Slide Mechanics

Name the type of motion undergone by a door being opened and closed

Rotary: all parts of the object move at the same time, same direction, but different distance. Ex: flexing of the knee or elbow. Clinical application: pick a point close to the elbow (1) and pick a point farther away from the elbow (2) and see the distance traveled by each point. Point 2 will travel a longer distance than point 1.

a single point (or points) on one articular surface contacts multiple points on another articular surface

Slide (Glide)

single point on one articular surface rotates on a single point on another articular surface

Spin

Mechanical Analysis Of Force: Parallel Force Systems

Splints - use parallel force system to stabilize joints Parallel forces of the body brace: force x and y (click) are parallel in the same direction while force z (click) is parallel but in the opposite direction. Force z must be in between forces x & y to provide stability. If force z were at either end, instead of the middle, motion would occur (defeating the point of wearing the brace/splint).

First-class lever

The effort force and resistance force are on either side of the axis 1st Class Lever system...in body is rare. First class lever - think balance. Goal: Reduce the effort required Effort force - the force pulling in the direction of the movement Resistance Force = that which is attempting to resist motion Think: balance Rare in the body

Torque Calculation

Torque = (force) x (moment arm) Moment arm = Perpendicular distance from the muscle's line of pull to the axis of motion

Name the type of motion undergone by a leg as it swings forward in gait

Translatory - curvilinear: combination of translatory and rotary motion in which "the entire object is moving in a linear fashion and the individual parts are moving in an angular fashion" (Lippert, 2011, p. 6). Clinical application: Consider taking a drink of water without translatory (linear) components

Name the type of motion undergone by a patient when riding in a wheelchair

Translatory - rectilinear: all parts of the object move at the same time, in the same direction, and at the same distance. Ex: person on a sled.

a. How much effort (more or less) is needed to push the pole down? Less force is required to push the pole down because the effort arm is longer than the resistance arm. b. What type of lever is this? First class lever. c. Is there mechanical advantage? Yes. Jackson has good mechanical advantage.

What happens when the effort arm is longer than the resistance arm? a. How much effort (more or less) is needed to push the pole down? b. What type of lever is this? c. Is there mechanical advantage?

a. How much effort (more or less) is needed to push the pole down? More force is required to push the pole down because the resistance arm is longer than the effort arm. b. What type of lever is this? First class lever. c. Is there mechanical advantage? No. Jackson has poor mechanical advantage.

What happens when the resistance arm is longer than the effort arm? a. How much effort (more or less) is needed to push the pole down? b. What type of lever is this? c. Is there mechanical advantage?

It increases the perpendicular distance (moment arm), thus increasing the torque. Remember: torque is a rotational force generated in a joint.

What is the advantage of having a patella?

MECHANICAL ADVANTAGE

When MA > 1 then good MA: wheelbarrow (2nd class lever) When MA < 1 then poor MA: tweezers (3rd class lever)

You are going through a revolving door. Describe where you would place your hand to make the task as easy as possible. Why does this hand placement work?

You would place it closest to the outer edge of the door. It is easier because it increases the length of the effort arm relative to the resistance arm, thus increasing the mechanical advantage. *Try it with a door (push the door closer to the axis; push the door closer to the edge).

Force Vector

a pictorial representation of the point of application, direction and magnitude of a force •a straight line segment whose length is magnitude and whose orientation in space is direction •Definition - "one who carries or conveys, carrier"

Mechanical advantage is defined as____________________

a ratio between the effort arm and the resistance arm (EA/RA) good, if the ratio is greater than one (1) •MA is a ratio between the effort force and the resistance force •(the factor by which a machine multiplies the force put into it) •MA = distance from input force to fulcrum ÷ distance from output force to fulcrum Larger the effort force arm relative to the resistance force arm, the better the mechanical advantage Measures the efficiency of the lever ●A RATIO between the effort arm (force) and resistance arm (force) Relative effectiveness of the effort force compared to the resistance

Which involves all parts of an object moving in a straight line, at the same time, and the same distance?

rectilinear motion

Clinical Application - Concurrent Forces

splint (dynamic) with finger loop

Mechanical Advantage: Clinical Application

•Less (effort) force is required if •you put the resistance as close to the axis as possible •and apply the effort force as far from the axis as possible Example: wheelbarrow (OVERHEAD with bricks) •Brick placement changes the length of resistance arm •even though the effort force (where you place your hands on the handles) remains the same carrying box •Which takes less energy, holding the box 2 inches form your body or 10 inches? •At 10 inches the resistance arm is longer •more (effort) force is required •poor MA

Torque - Rotation of a lever depends on magnitude of the force and distance of force from the axis

•Torque •simply stated: the ability of a force to cause rotation of a lever •Wrench picture: if the bolt you are loosening is stuck, what options do you have to create more power? •The twisting force (torque) exerted by the wrench can be increased by: •increasing force applied to handle (Pull harder), or •increasing length of the handle (increasing moment arm) •Torque: Assuming Muscle A and Muscle B have the same amount of force, Muscle B would have greater Torque (ability to rotate the arm/flex the elbow joint) because of the longer Moment Arm (Perpendicular Distance between axis and line of pull) Moment arm is a lever arm This is a pictorial representation of a longer moment arm Moment arm = effort arm = force arm (at 90 degrees) •If the force were directed exactly through the axis of rotation •No torque would be produced. •(i.e. pushing into a door at the outer edge)

Passive Motion

○generated by something other than muscle activation, i.e. gravity, another person, another part of the person's body, etc. Describe PROM after CVA vs. AROM after wrist fx for example...

Lesson Objectives

● describe the difference between kinematics and kinetics. ● name and define internal and external forces which affect motion. ● describe and identify the types of joint motion related to translatory and rotatory movement. ● describe the roll and slide mechanics for convex-on-concave and concave-on-convex motions. ● define and give a functional or clinical example of open-chain and closed-chain movement. ●define magnitude, direction, and point of application of a force, and describe how force vectors are used. ● describe and identify linear, concurrent, and parallel force systems as they apply to anatomical, functional, and clinical situations. ●describe a force couple, and provide an example of one in the human body. ● define base of support (BOS) and describe its impact on function. ● estimate the location of an individual's center of gravity (COG) in any position, as well as the COG for each segment of the body. ● determine the class of a lever system from a functional or clinical example, and identify the axis, effort force, resistance force, effort arm, and resistance arm. ● explain the concept of mechanical advantage and its functional significance ● explain the differences between and the clinical significance of internal and external torque. ● calculate the internal and external torque given a clinical scenario or functional activity ● describe the effects of force on a joint (compression, distraction, and rotation)

External Torque

●"product of the external force (such as gravity) and the external moment arm" In this case, the external torque is gravity...the external lever arm in B is shorter than A because the center of gravity (of the forearm) is closer to the axis of the joint if you're measuring at a right angle/perpendicular distance between the axis of the joint and the center of gravity of the segment External torque of A is larger than B.

Moment Arm is a Lever Arm; HOWEVER....

●Do not confuse the moment arm with an effort arm ○The length of an effort arm DOES NOT CHANGE ■It is always the distance from the axis to the point of application of the effort force in a lever system ○A moment arm CHANGES every MOMENT ○ When you are talking about TORQUE specifically, think: moment arm (muscle power) When you are talking about LEVERS, think: effort arm (effects on a joint related to structure) ○

Force & Moment Arm Defined

●Force - "a push or pull that can produce, arrest, or modify movement" (Neumann, 2010, p.11) ●Moment Arm - perpendicular distance from the muscle's line of pull to the axis of motion perpendicular distance (which means....drawing a line between the axis of rotation and the line of pull)...intersecting at a right angle with the line of pull

Rotation

●Rotation (angular)-same time, same direction, different distance Rotation: circular path of motion around a pivot point (click; like a spinning top); all points of the body simultaneously rotate in the same direction (click) for example: flexing and extending the elbow (distal (hands) move a greater distance than proximal forearm) **Many synonyms for non-axial motion exist, such as glide, slide, translation and linear motion. All are used commonly in the field of kinesiology, so it is useful to be familiar with all of them. Movement in the body is rarely only 1 movement • roll & glide often go together •Spin can occur on its own

Translation

●Translation (linear)-same time, same direction, same distance Translation: describes a linear motion in which all parts move parallel to and in direction as every other part Describe the two types: - Rectilinear - Curvilinear

Force Couple During Scapular Upward Rotation

●Upper trapezius - elevation, upward rotation, assist with adduction ●Lower trapezius - depression, upward rotation, assist with adduction ●Serratus anterior - abduction, upward rotation Neutralizing forces will result in "upward rotation" of the scapula!

Internal Torque

"product of the internal force (muscle) and the internal moment arm" Same muscle will also have different "torque" in different positions.... Torque: Force = muscle contraction Moment arm = perpendicular distance (which means....drawing a line between the axis of rotation and the line of pull...intersecting at a right angle with the line of pull) Whatever "force" your muscle contraction generates, multiplied by the distance from the axis of rotation to the line of pull (at a right angle), will give you the TORQUE...so according to this, and assuming the muscle

Linear Force System

- 2 or more forces act upon an object in the same line Parallel & same point of application; go in the same direction gastroc & soleus both work in the "same line" and serve to plantarflex the foot, roughly the same point of application psoas & iliacus are both hip flexors both work in the "same line" and both provide a linear force system, roughly the same point of application

Pull-Tension/Distraction

- A PULL - causing tension between two surfaces Such as PULL...distraction - Tension or distraction with a pull up

Forces may be:

- EXTERNAL or INTERNAL External - gravity, water, air/wind, other people, friction and atmospheric pressure Internal - contraction of muscles, force of ligaments, bones... Force is a vector

Center of Gravity of Body Segments

- Each segment is acted upon by the force of gravity and therefore has its own COG - COG = approximately 4/9ths or 45% of the length of the segment measured from the proximal end - As soon as one moves out of anatomical position, COG changes

Forces may

- May INITIATE a motion (click) or STOP a motion (click) - May PREVENT a motion (click) Initiate by pushing a person in a w/c A wall may stop a ball thrown at it.

Third-class lever

- The effort arm is always shorter than resistance arm. - Most levers in the body are third-class. - They are not very energy efficient. - They can move through a large range of motion. Effort force and resistance force are on same side of the axis. Effort force lies between the resistance force and the axis of rotation. •In third class lever •Axis at one end, effort force in the middle and the resistance at opposite end •Effort arm will always be shorter than the resistance GREATER MOVEMENT, but NOT MUCH POWER (Takes a lot of effort!) •Most levers of the body are third class levers because they are effective at producing rotation of the joint through a large arc/ROM •Large arc/ROM •Large energy expenditure/demand for muscular force •2nd class levers, in contrast •very energy efficient...think how easy it is to move a heavy load on a wheelbarrow. •Increase efficiency; however, decrease ROM •tradeoff - not very effective in moving the rigid bar through a large arc of motion •e.g. wheelbarrow •IT IS IMPORTANT TO be able to evaluate the relative energy efficiency of levers. •We can do that using the concept of mechanical advantage (leverage). WE WILL DO THAT SHORTLY. FIRST..... R A E

Push-Compression

- causing compression Such as PUSH... Compression of arm during a push up

Torque

- the ability of a force to cause rotation of a lever - is dependent on the magnitude of the force and the distance from the axis that the force is applied Two components: 1. Force 2. Moment Arm (Lever Arm) Force is generated by muscle contraction and together with the moment arm, produces torque (f) x (moment arm) = torque Force x moment arm = torque According to Neumann: GENERALLY SPEAKING: •Torque can be considered a rotary equivalent to a force •A torque rotates an object just like a force pushes and pulls an object in a linear fashion NOTE: Do not confuse MOMENT ARM with EFFORT ARM. An effort arm is always the same (it's the distance from the axis to the muscle's insertion). That distance will not change when the movement of the bone(s)/joint changes....but a moment arm changes from MOMENT TO MOMENT. We'll talk about this more as we go....

Point of Application

- the exact point at which the force is being applied

Magnitude

- the quantity of the force that is being exerted

MECHANICAL ANALYSIS OF FORCE

1. Linear Force Systems 2. Parallel Force Systems 3. Force Couple 4. Concurrent Force Systems

a. List three different factors that will affect her stability once the train starts moving. Center of gravity, base of support, and weight of the load she is carrying. b. How can she change her body position to reduce the risk of falling onto the lady next to her? Ex: Get low, bend her knees, widen her stance, put the groceries down, use external support (hold on to pole, lean against pole/wall), maintain her center of gravity within base of support.

Abra just finished grocery shopping and boarded the Metro Redline on her way home. a. List three different factors that will affect her stability once the train starts moving. b. How can she change her body position to reduce the risk of falling onto the lady next to her?

AKA: rotatory, rotary, rotational, circular, or axial The production of rotary movement is a primary function of the musculoskeletal system (muscles). However, movement is never pure rotary - we call it rotary for simplicity. Example - As the shoulder Abducts - the humerus actually slides downward slightly from the socket; most joints roll and slide. I will show you a picture of this later.... (click) ROLL =a tire rotating across a stretch of pavement (click) SPIN = a rotating toy top on one spot on the floor (click) SLIDE = glide MOST joints do both: roll & slide!

Arthrokinematic Motion

Biomechanics

BIOMECHANICS = Study of mechanics in the human body... Consists of : kinematics and kinetics (click) Kinematics - osteokinematics: describes the path of the moving bones Arthrokinematics: the motion that occurs between the articular surfaces of joints. We will be discussing the types of motion (axial or non-axial) today (click) (click)Then we will look at KINETICS (click) - we are going to analyze the components of forces We will look at the Mechanical Properties of forces or lever systems, and the efficiency of levers in the human body called Mechanical Advantage. We will also talk about how forces produce both rotary and translatory motions in the body... how to determine which type of motion is happening and the clinical implications to all of this: IT'S A BIG DAY!

Factors Affecting Stability

BOOKMARK THIS PAGE! Clinical relevance! As you will see from some coming examples. Height of the COG above the base of support. •HIGHER COG=LESS STABLE, Lower COG=MORE STABLE A small person crawling on hands and knees is most stable because the COG is very close to the floor •Think of the position of blockers and tacklers in football, during a block or a tackle, they remain low so that they are their most stable. •Clinically, we often work with people who have had strokes (CVA -cerebrovascular accident) which may affect their balance. When we first start working with them, we may do so in positions such as supine, prone, or sitting as these ensure a lower center of gravity than does the position of standing. As balance progressively improves, we can transition to work in standing. Size of the base of support. •NARROWER Base of Support=LESS STABLE, WIDER Base of Support = MORE STABLE •Here we can go back to the example of a person crawling (not only does that bring the COG closer to the floor) but it has a wider base of support extending from the arms to the legs. •this is very important clinically. You will see people with balance problems who automatically compensate by spreading their legs while they walk in order to broaden their base of support...need to recognize and think: benefits and problems. •The base of support can also be broadened by the use of canes, crutches, and walkers. But doing so results in a significant limitation with respect to use of the upper extremities...and other things. Location of the gravity line within the base of support. As gravity line moves outside the base of support, LESS STABLE; gravity line towards center of BOS, MORE STABLE •In humans, COG can fall outside of the body •When it does, the imaginary line of gravity's pull that extends from the COG to the floor often falls outside of the individual's base of support. •This is an unstable position. Examples would be standing on a platform and leaning to the left. Must either widen the BOS or extend/abduct the R arm to counterbalance, of you'll fall off! Relationship of COG/line of gravity to BOS: OVERHEAD OF BOOK ON THE TABLE A.The book is very stable because its COG is in the middle of its BOS B.The book is less stable because the COG is near the edge of its BOS C.The book is unstable and will fall because its COG is beyond its BOS Example: when it's really windy, what do you do to stand at the bus stop so you don't fall? Weight of the body •Whenever weight is added to the body, it shifts the COG •Clinically, whenever we add a weight (or tool, device) to a patient, we are shifting the patient's COG. We need to be aware of how this may affect stability.

Three Types of Levers

Before we look at mechanical advantage, let's review levers! EARS ARE AERO-DYNAMIC! 1st: see-saw 2nd: wheelbarrow 3rd: tweezers OVERHEAD of door, neck, leg for three different lever exercises OVERHEAD of: biceps concentric biceps eccentric

•In a perfect sphere, cube, or rectangle, the COG coincide with the object's geometric center (click). For example, in trying to balance a volleyball or pencil on our fingertips, the COG is that point at which the ball and pencil perfectly balance. If you have a SOLID object or segment, the COG will remain unchanged despite the position that object takes in space. •However, if the object changes in shape or distribution of weight, the COG changes...volleyball run over by a car, pencil sharpened many times... (click - bat, click - crutch) OVERHEAD OF COG (BALLS & CRUTCHES)

Center of Gravity

Pecs in Action

Clavicular portion of the pectoralis major results in flexion and horizontal adduction Sternal portion of the pectoralis major results in extension and horizontal adduction. Together: horizontal adduction

Closed-Chain: Movement of proximal segment about a relatively fixed/stationary distal segment. Closed chain: distal joint of a bone is fixed in some way resulting in proximal bone having to move when movement occurs at that joint. Very common in LE. Ie, squat, get up from a seated position

Closed-Chain Motion

The skateboarder's entire body is moving down the street in a linear fashion (click), while individual joints on the "pushing" leg (click) (ie, the hip, knee, and ankle) rotate about their axes (angular/rotatory motion) Another example of combined translatory & rotatory motion is walking. The whole body exhibits linear motion walking from point A to point B, while the hips, knees, and ankles exhibit angular/rotatory motion. According to Lippert, generally speaking, most movement within the body is angular/rotatory. Generally speaking, movement outside the body tends to be linear. Some sources say "curvilinear" is the most common type of movement in the body. What does this all tell us? We don't move like robots!

Combination of Translatory & Rotary Motion

Palm in the shape of a "c" is the concave Closed fist is the convex

Concave & Convex

The concave member rolls & slides in similar directions Shown on the slide above: A.Open chain - someone swinging knee back and forth (concave on convex) Closed chain - someone sitting down with foot on the floor and stands up (convex on concave) - (not shown on this slide, but get up and try it!)

Concave on Convex

Top picture is convex on concave Bottom picture is concave on convex

Convex-Concave Rule

Effects of Force on a Joint: Biceps Brachii

Earlier we mentioned that forces either push or pull, and this can also be seen when forces act on a joint. The type of force depends on the angle of the force vector. When we look at the effects of force on a joint, we are looking at the angle between the moving lever and the line of pull as seen in purple -(click) NOT the angle of the joint This means that on the picture to the right, we are not looking at the angle of the humerus (click) and the forearm (click)--the moving lever. Instead, we are concerned with the angle of the moving lever (click) and the line of the pull of muscle force (click). Depending on the angle, these forces may cause either compression, rotation, or distraction of the joint...

Effort Force

Effort Force = that which is attempting to cause motion •Effort force - the force pulling in the direction of the movement •Often difficult to determine which is the effort force and which is the resistance force •Effort force - Always the winner in the torque game •Resistance force - Always the loser in producing rotation of the segment •When there is equilibrium, the distinction is arbitrary... •Movement will cause rotation •will always occur in the direction exerted by the effort force •unless at equilibrium. EXAMPLE ABOVE HAS DIFFERENT AXIS POSITION compared TO OUR PREVIOUS SLIDE •Depending on where the forces are in relationship to the axis • levers can be classified into three classes

Second-class lever

Effort force and resistance force are on same side of the axis. Resistance force lies between the effort force and the axis of rotation BOTH SECOND AND THIRD CLASS LEVERS HAVE AXIS ON ONE SIDE CLASSIFICATION DEPENDS ON WHERE THE RESISTANCE AND EFFORT FORCES ARE...so that's what you have to figure out •2nd Class lever •Effort arm is always longer than the resistance arm •Effort force is always further away from the axis than the resistance force •Effort force causes motion •Wheelbarrow If E is greater than R ... think POWER LESS MOVEMENT< BUT MORE POWER

a. In which position is the external torque (torque of gravity) greater? Position #1 - the moment arm is longer in position #1 compared with position #2. b. Which position would require more muscle force of the hip extensors to overcome the torque of gravity? Why? Position #1 - because you have to overcome more torque of gravity (longer moment arm). c. Which position would you recommend to your patient? Position #2 - because you want less effort and strain on the back on the patient's part. More efficient, safer for client, and prevents injuries with proper body mechanics and ergonomics.

External TorqueIn order to lift a box, you will need to overcome the torque of gravity and the weight of the box. You are an occupational therapist working with a client on body mechanics. Look at the two pictures below. a. In which position is the external torque (torque of gravity) greater? b. Which position would require more muscle force of the hip extensors to overcome the torque of gravity? Why? c. Which position would you recommend to your patient?

True/False: When the angle formed by the moving part and the line of pull of a muscle is greater than 90 degrees, there is a compressive force on the joint.

False

a) The axis: cervical spine/neck b) The effort arm (force arm): cervical spine to the insertion of the posterior neck muscles c) The resistance arm: 4/9 of the distance from the axis of the neck to the tip of the nose d) The class of lever represented: first class lever

For raising head to neutral from a flexed position using posterior neck muscles, identify: a) The axis b) The effort arm (force arm) c) The resistance arm d) The class of lever represented

a) The axis: MTP (metatarsal phalangeal) joints/toe joints b) The effort arm (force arm): MTP to the insertion of the ankle plantar flexors c) The resistance arm: 4/9ths of the distance from the heel to the axis (MTP joints) d) The class of lever represented: second class lever

For rising onto tiptoes, identify: a) The axis b) The effort arm (force arm) c) The resistance arm d) The class of lever represented

a) The axis: elbow joint b) The effort arm (force arm): elbow joint to the insertion of the biceps c) The resistance arm: 4/9 of the distance from the elbow joint to the fingertips d) The class of lever represented: third class lever

For the arm being flexed at the elbow by biceps, identify: a) The axis b) The effort arm (force arm) c) The resistance arm d) The class of lever represented

Center of Gravity in People

Generally lies a little anterior of S2 vertebra •approx. 6" above pubic symphysis •Basically at the point where all planes of the body intersect Exact location varies •varies with each individual's body build, age and sex •Generally, people who are biologically male tend tend to have COG slightly higher than that of biological females since men lack breasts and generally do not have the wider pelvises of women COG changes over time •As one grows and body proportions change, so does one's COG •Similarly, if degeneration of the vertebrae leads to a shortening of overall height during aging, the COG lowers. OVERHEAD OF SACRUM & PERSON BENDING

This is ALL slides of Glenohumeral Roll/Glide - click 1x and it should play through the following pictures

Glenohumeral Roll/Glide

This is ALL slides of Glenohumeral Roll/No Glide

Glenohumeral Roll/No Glide

Now we will be concentrating on a major external force that influences movement of the body = GRAVITY GRAVITY = The attraction of the earth for objects within its sphere of influence...pull of the earth.. •In kinesiology, we are very concerned with the effects of the earth's pull upon the body. This leads us to the concept of the center of gravity...

Gravitational Force

anatomical pulleys

Increase the internal moment arm Bone or boney prominence that changes the direction of pull of a muscle (and therefore changes the moment arm). Anatomical pulleys change the direction of line of pull without changing the magnitude of applied force. Visualize the line of pull / action line of a muscle at the point of attachment. Vectors are ALWAYS straight lines. OVERHEAD: moment arm with patella greater than without one = greater MA (mechanical advantage) OVERHEAD: lateral malleolus acts as a pulley allowing the peroneus longus to change its direction of pull

Position A has the most torque (rotary force) because it has the longest moment arm/perpendicular distance. Torque = (F) x (moment arm)

Internal Torque: In the pictures below, in which position can the biceps generate the most torque (given the force is equal), and why?

Application of Force Couple

Jar lid turning - •the fingers (force A) and the thumb (force B) unscrewing a jar lid. •jar lid in the right hand •fingers move left •thumb moves to the right •together they move the jar lid in a counter clockwise direction

This is ALL slides of Knee: Roll/No Glide

Knee: Roll/No Glide

Force Vectors

Label: humerus, elbow, forearm, point of application (insertion of the muscle), bicep = line of pull (direction), and magnitude (dpeends on force exerted by biceps) Label: table pushing up against the book, mass of book against the table, gravity pulling down, point of application (where finger touches the book), magnitude & direction = arrow, friction between the table and the book & between the finger & the book Between the line of pull and the moving part is the angle to focus on.

Effects of Force on a Joint

Label: humerus, forearm, biceps (insertion of biceps = line of pull) Compression: Less than 90 degree angle, FORCE=PULLING FORCES that compresses the humerus and forearm (LINEAR with some rotary, very rarely purely one or the other) Rotation: Pure rotation at 90 degrees Distraction: at above 90 degree angle, FORCE=PUSHING Forces that push the humerus and forearm apart (LINEAR with some rotary, very rarely purely one or the other) _______________________________________________________________ Example of an Elbow (smooth movements, coordinated, gradually changing forces (as one force increases, one force decreases) Forces which produce translatory movement (0-90) (click) Forces which produce rotary movement (90 degrees) (click) Forces which produce translatory movement (90-150) ***Pure rotation occurs when line of pull is at 90 degree angle to part being moved

NEWTON'S LAWS OF MOTION

Law of Inertia - Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it. - Passenger in a car: if the car stops all of a sudden, the body is thrown forward & the neck would flex - with risk for whiplash - The stopping force overcame the inertia of being in motion Law of Acceleration The acceleration of an object is proportional to the unbalanced forces acting on it and inversely proportional to the mass of that object. Acceleration = Force/Mass Force = Mass X Acceleration Force = mass x acceleration or a change in velocity •Velocity of an object changes when it is subjected to an external force. •Massive object is harder to accelerate/move •Force determined by how heavy and how fast •(remember that mass is the property of a body that causes it to have weight in a gravitational field) •Velocity change depends on the mass of the object •Force causes change in velocity & Vice-Versa •For an object with a constant mass m •the force F is the product of an object's mass and its acceleration a: •a = F / m, or... F = m a Law of Reaction For every action, there is an equal and opposite reaction Reaction - for every action there is an equal and opposite reaction Example: jumping on a trampoline: the higher you jump, the higher you rebound •Heel exerts force on the floor and floor exerts equal and opposite force on the heel •Downward force of the book on the table and table up on book •Stable /Equilibrium •Strength of the reaction •always equal to the strength of the action •occurs in the opposite direction; but they have the same line of action •e.g. Woman with suitcase - to balance weight of case •must shift COG and AB duct arm to create an equal reaction in the opposite direction

What are the four force systems that occur in the body? Give an example found in the body for each. Be able to explain this to other members of your group.

Linear forces, ex. Plantar flexors (soleus and gastrocnemius), hip flexors (Psoas & iliacus = iliopsoas); 2 or more forces acting upon an object in the same line. Concurrent forces, ex. Deltoid (anterior and posterior), Pectoralis major (clavicular & sternal); two or more forces act at a common point of application, but in divergent directions. Parallel forces, ex. Abdominals and back extensors, neck flexors and neck extensors; two or more parallel forces act on the same object in the same plane, and in the same or opposite direction, and do not touch/intersect. Force Couple, ex. Upward rotation for the Scapula (Serratus Anterior, Upper Trap, Lower Trap); when two or more forces act with neutralizing force in different directions resulting in a turning effect.

THIRD-CLASS LEVERS

Most of the body has third-class levers Large arc/ROM Less efficient (a lot of force required)

The resistance arm (backpack) is now between the axis (back of the chair) and the effort arm (Jackson's muscles). As a result, this has switched from a first-class lever to a second-class lever. Because the resistance force is now pushing down on the SAME side of the axis, you need to pull UP in order to overcome the resistance force. Try it!

Now place the weighted item on the pole between the chair and the person holding the pole. How did the elements of the lever system change (resistance arm, effort arm, type of lever)?

Mechanical Advantage: Clinical Application Pt 2

OVERHEAD: biceps vs. brachioradialis • (click)Illustration a: mechanically inefficient 3rd class lever (favors distance) • produces large arc of movement of lever distally •(click)Illustration b: mechanically efficient 2nd class lever (favors force) •produces little increase in the arc distally OVERHEAD: ramp & incline Inclined plane as a wheelchair ramp: A. (click)A longer ramp requires less force but greater distance B. (click)A shorter ramp requires more force but shorter distance *What is gained in force, is lost in distance *Clinical application of a ramp - rise over run

Open-Chain: Movement of distal segment on a relatively fixed proximal segment. Open chain: distal bone of a joint is free to move (sitting down and swinging knee)

Open-Chain Motion

Direction

- the line of the force