Functional Movement Exam 1 2/2

Mechanics

The study of forces and motions produced by their actions

biomechanics

The study of forces and motions produced by their action applicable to the structure and function of the human body

Why biomechanics is important to OT?

OT assessments and treatments involved understanding and analyzing movement.

Force

Push/pull of an object that can cause it to move, change its speed and change its direction. F=m(a)

Inertia

Amount of energy required to alter state of velocity of the body

Translational Force

When the center of mass moves from one place to another. Linear force is linear motion along a straight line, such as pushing or pulling objects (i.e. pulling open a drawer)

Rotational Force

Object that moves in a circular motion about its center of mass around an axis.

Torque

The measure of the force which causes something to rotate around a point (i.e. turning a doorknob, opening a jar lid)

T/F: Performing a bicep curl involves a rotational movement about the elbow joint

True

Mass

The amount of matter that makes up a body

Acceleration

The rate at which velocity changes (not how fast an object is moving)

Center of Mass (CoM)

Point where all mass is equally distributed, in anatomical position this is just anterior to 2nd sacral vertebra. COM of larger bodies change with movement.

Center of Gravity (CoG)

Theoretical point where the effects of gravity are balanced, lies closer to the end with more mass

Mass moment of inertia

resistance to a body's rotation about an axis (angular velocity)

Factors contributing to mass moment of inertia

-Mass of body and distribution of mass of body (distance of CoM from AoR) -The larger the moment of inertia, the more effort is required to change the rotational motion.

Torque equation

Rotational movement: Torque=mass moment of inertia* angular acceleration

Torque=Force *moment arm (distance)

Moment arm

Perpendicular distance between the axis of rotation and the line of force applixation

Which of the following is not true about torque? A. Torque is a measure of rotational force B. Torque is calculated as mass moment of inertia multiplied by angular acceleration C. Torque is always equal to the applied force D. Torque is the product of force and moment arm

C. Torque is always equal to applied force

When loosening a nut with a wrench, where is the axis of rotation located?

Through the center of the nut

Newton's First Law of Motion

An object at rest will stay at rest and object in motion will stay in motion at a constant velocity unless acted upon by an external force

Law of inertia

The tendency to do nothing/ remain unchanged (nothing moves unless a force is acted on it)

linear inertia

An object at rest will remain at rest, and an object in motion will continue to move in a straight line at a constant speed unless acted upon by an external force

Rotational inertia

A body remains at rest or at a constant angular velocity around an axis of rotation (AoR) unless an external force (torque) alters its state

Newton's 2nd law of motion

The harder you push or pull an object, the faster it will accelerate, and the heavier the object is, the slower it will accelerate for a given force.

Acceleration of an object is _____ proportional to the force applied to it and _____ proportional to its mass

directly; inversely

How does Newton's Second Law of motion apply to how an object responds to linear forces?

Linear acceleration of a body is directly proportional to the force causing it, occurs in the same direction as the force, and is inversely proportional to the mass of the body.

How does Newton's second law of motion apply to how a body responds to angular forces?

Angular acceleration of a body is directly proportional to the torque causing it, occurs in the same rotary direction, and is inversely proportional to the mass moment of inertia.

Moving a cuff weight closer to the AoR will ______ mass moment of inertia/distance from AoR

decrease

Less muscular force will be required to move an extremity that is ______ than one that is in full ))))

flexed/shortened, extension

Newton's Third Law

For every action, there is an equal and opposite reaction (forces always exist in pairs). When one object exerts a force on a second object simultaneously exerts a force of equal magnitude but in the opposite direction on the first object.

Ground reaction force

Push from ground when moving (i.e. walking/standing, body pushes against ground ←→ ground pushing against body) amount and magnitude of reaction is equal and opposite from feet onto the ground.

Joint reaction

Internal force within joints, push and pull is occurring within a joint due to pressure of bones against each other. When moving joints (lifting, pulling), joint reacts to forces you are performing

Internal Torque

Force of muscle contraction

External Torque

External forces

Internal moment arm

Lever muscle used to create the movement, the moment arm within yourself (i.e. muscle pulling on bone to move elbow; distance between where muscle attaches to the bone and the center of elbow joint)

External moment arm

Distance between the forces, the point of application (i.e. distance between where you're holding the weight and elbow joint). Lever external forces are used to counteract the torque you're trying to generate within your muscles.

Function of lever external forces

Counteract the torque that the muscles are trying to generate

What is an example of internal and external torque being equal

Lifting the elbow up in the air while in a bent position, the bicep (ITQ) wants to lift it up into flexion, gravity (ETQ) has a tendency to pull the arm down into extension. Whether the arm moves up or down depends on which torque is stronger. If torque are equal, joint stays still in static equilibrium (ITQ=ETQ)

What is an example of ITQ exceeding ETQ?

When lifting a weight to keep the elbow in flexion, ITQ needs to be greater than ETQ generated by gravity

What is an example of ETQ exceeding ITQ

When holding the position of an elbow in mid-flexion for a while, gravity pulls the arm down and ETQ starts exceeding ITQ and the elbow moves into extension.

In the bicep example, an arm is staying in position because

ITQ=ETQ

Where is the position of greatest torque?

Position of 90 degree angle where the moment arm and angular force is greatest. All of the force goes into rotating the arm.

How does stabilizing force vary with joint angle?

When pulling into extension, the moment arm decreases and force is present but serves to stabilize the joint as force goes back to the joint to keep two bones together. When a muscle is going into extension.

How do distracting forces vary with joint angle?

When pulling into flexion, force is distracting rather than stabilizing because the joint force is directed away from the joint.

Function of stabilizing force

Counteract potential joint displacement

What determines muscle action

Layout of the muscle fibers in relation to the bones they pull

Lever

A rigid bar that rotates around an axis (fulcrum) → converts a linear force to a rotary force (torque). Helps determine application or removal of force as therapeutic interventions.

3 components of a lever

Fulcrum(joint), Effort (moving or holding force: muscles/internal force), Load(resistance force)

We _____ leverage by applying a force close to a pivot point/fulcrum axis and _____ leverage by applying the same force further away

lose, gain

Fulcrum

The fixed point where the lever arm pivots or moves

When sitting on a seesaw, whoever weighs ____ needs to be closer to the fulcrum point to create a balance

more

Change in distance between axis of rotation creates

balance point

First class lever

axis is centrally located, provides equal forces, the force with the longer arm has an advantage (i.e. seesaw).

Second class lever

moment arm of the resistance (E) is always shorter than the moment arm (lever) of the applied force (I) → muscle (internal force) has greater leverage than external force (load). Resistance lies between the force and axis, axis is at one end of a bone. Large weight can be moved by a smaller force. (uncommon in the human body ex. Metatarsophalangeal joint) (i.e. wheelbarrow)

Third class lever

Most common in the human body. Resistance arm is always longer than the force moment arm → mechanical advantage is with the resistance force (not the muscle) . Advantage is speed.

For a lever to be a first class lever, the fulcrum needs to be

between the load and the effort

In a second-class lever, the moment arm of the resistance is always shorter than the moment arm of the applied force (I.e. muscles as the internal force). What does this imply?

The lever will provide a mechanical advantage

In a second class lever, the load is between the fulcrum and ____

effort

Which body parts acts as the fulcrums of levers

Joints

Importance of levers

Levers create an advantage of either force or distance in motion Third class levers can displace a load with minimal contraction or move objects a larger distance. Repetitive work is supported, but it may come at a cost to bone health for example.

What is mechanical advantage (MA)

The ratio between the internal moment arm and external moment arm

MA of first class lever

MA depends on location of axis

MA of second class lever

Internal force < External force to balance ---> MA more than 1

MA of third class lever

Internal force > External force to balance ---> MA less than 1

Mechanical advantage (MA) is the ratio of the internal MA to external MA (MA=IMA/EMA), if MA: 8 cm and EMA: 16cm, MA=?

0.5 (for every unit of input force you apply, you gain half a unit of output force)

Free body diagram

Sketch of body and environmental forces

Internal forces in a free body diagram

Active: stimulated muscles Passive: tension from stretched tissues (joint capsule, intramuscular CT, ligaments)

External forces in a free body diagram

Gravity: the weight of an object or body segment, externally applied resistances, friction, air resistance, ground resistance

Vectors in a free body diagram

Indicate force in regards to magnitude, spatial orientation, direction, point of application

Direction+Spatial Orientation=

Line of force/line of gravity

Joint reaction force

force that exists at a joint, developed in reaction to the net effect of internal and external forces,, often opposite the direction of the dominant muscle force

Co-linear

When forces are in the same line

Co-Planar

When forces are in the same plane

Concurrent

If forces are not co-linear nor co-planar, contains forces whose line of action meet at some point, forces may be tensile (pulling) or compressive (pushing)

Example of concurrent force system

Deltoid, Pec Major, and Rotator cuff all exerting force on the shoulder joint from various directions. Forces are not in the same line/plane and have their own unique angle of pull but converge at the shoulder joint allowing us to move and perform motion.

Splinting and the significance of linear and concurrent force systems

Correcting the line of pull

Agonist

muscle or group of muscles most directly associated with initiation of movement, prime mover

Antagonist

muscle or group of muscles that have the opposite action of the agonist.

-must relax to allow force of agonist to enact movement

-eccentric activation at end range slows/stops movement of agonist to protect joints

-controls movement when gravity is prime intiator of movement.

Synergists

muscles that cooperate during movement to produce a desired result. Move in a similar fashion to the agonist, block undesirable action of the agonist, provide stabilization of proximal joints.

Identify agonist, antagonist, and synergist muscles while holding onto the MARTA pole

agonist: finger flexors antagonist: finger extensors synergist: wrist extensors stabilzie pole

stable equilibrium

body position is altered, but returns to COG

ex. rocking chair

unstable equilibrium

body position is altered and does not return to COG

ex. sitting on a narrow base stool and leaning forward will tip you off stool

Neutral equilibrium

the COG is displaced, but remains at the same level (person in a wheelchair, COG remains the same since they're still sitting

Decreasing lever arm or moving load closer to axis of rotation will ____ amount of torque requried to move the limb.

ex. putting weight at forearm vs. hand

decrease

Factors that impact stability of the body

1. Height of the COG above the base of support

2. Size of the base of support

3. Location of gravity line within the base of support (vertical line of pull from COG)

4. Weight of the body

Situations that promote stability

Low center of gravity, wide base of support, gravity's line over the center of the support, heavy weight

Any deviation from anatomical position

will alter center of gravity

Base of Support (BOS)

area within the points of contact of the body and any object the individual relies on for support

Why intervene?

Prevent deformity or maintain current functional abilities

Restore capacity for motion

Compensate for limited ROM, strength, or endurance

Focus of treatment

ROM, strength, endurance

High-intensity, short-duration exercise

Strength

low intensity long duration exercise

endurance

repetitive eccentric activation

leads to high level of stress on the structures as we reduce # of muscle fibers recruited during active movement

Factors that impact loss

position of muscle: shortened=greater loss of strength

type of muscle: slow twitch fibers experience more relative disuse from immobilization because they're more heavily used in ADLs

How to address joint stability in therapy

ROM --> Strength --> Endurance

Muscle stiffness

resistance to stretch that leads to increased passive tension in a muscle

Flexibility

Muscular relaxation resulting from 'giving in' to a stretch

How to increase ROM (passive insufficiency)

a stretch force greater than current ROM must be applied to elongate tissue. Permanent changes in ROM=plastic change Temporary changes=elastic change

less force over a longer period of time leads to plastic change (With enough repetition)

Hellebrandt's overload principle

Strength increases only if the load is > than the typical load for the muscle and is applied to the point of fatigue.

Ways to achieve overload

Increasing resistance Increasing number of reps Increasing number of sets Decreasing time for rest between sets