Kinesiology: Physics, torque, vectors, etc.

– Law of Interia
– Law of Acceleration
– Law of Action-Reaction

– Body at rest remains at rest, body in motion remains in motion- unless acted upon by an external force

Ex: Cat sleeping on dashboard will stay sleeping on the it – unless person slams on brakes; then cat will go flying

– The relationship of an object’s MASS, ACCELERATION, and applied FORCE is represented by the equation: F = MA

– Objects with more mass require more force to move (accelerate)

Ex: Sumo wrestler preparing to challenge a small child

For every acton there is an equal and opposite reaction
– To obtain equilibrium, the forces acting on the object must be equal and opposite

Ex: metal pendulum balls
&
Impact of gravity on wheelchair positioning with person sitting in it

Pushing tissues together

Ex: Walking

Pull tissues apart

Pulling force that a muscle generates

Ex: Tearing of muscles

Twisting

Ex: neck, back

Sliding along surfaces

Ex; Axonal shearing in brain injury, chewing

Forces act upon the body to create STABILITY or MOBILITY

Used to indicate these forces KINETICS

Forces have a:
– Direction
– Magnitude

Forces create:
– Linear movement
– Rotary movement

The force that causes movement or is attempting to cause movement

Ex: When lifting arms = internal effort force is muscles

The force that opposes movement

Ex: when lifting arms = external force resistance would be gravity or any type of load

Forces that originate outside the body

Ex: *Gravity – most common; wind, water, other people, friction, exercise equipment (resistance bands)

Forces originating inside the body

Ex: muscles contractions, properties of tissues (i.e. ligaments), joints reaction forces

1. Absolute force produced
2. Distance applied from axis
3. Angle of application
Ex: speed of current/amount of water; speed of wind; number of muscles fibers contracting;

***amount of tension in soft tissues around joint (ligaments, tendons, skin, joint capsule, etc.)

The primary EXTERNAL force acting upon the body

– Voluntary movement is a neuro-muscular response to stimuli
– Gravity is one type of stimuli that causes muscle activation

Ex: Interaction between a child’s neuro-muscular system & gravity

The primary INTERNAL force acting on the body

– The force of muscle contraction serves to crete movement, slow movement, stabilize a body part or overcome the effects of gravity

-The force generated is influenced by the total tension of the muscle

Total tension

– Total = Active + Passive tension

– Determines the force of muscle’s contraction

Active and Passive Tension

Actual muscle force generated by the sliding filament mechanism (contractile actin/myosin)

*Muscle fibers have natural elasticity (think rubber band)

Inherent passive force within the muscle fibers themselves when STRETCHED

*Passive tension occurs when muscle is stretched beyond its resting length

*Muscle fibers have natural elasticity (think rubber band)

Passive tension= increases

Active tension = decreases

– Compressive
– Tensile
– Shearing
– Torsional

– Attempt to create movement around an axis

-Can be internal or external

*Muscles produce force to cause ROTATION of the shoulder joint to bring it into abduction

*However, gravity (and weight held in his hand) are the forces attempting to cause ROTATION of the shoulder joint back down to his side

-Muscle attaches via tendons to bones

-When a muscle is directed to contract, it exhibits a pulling FORCE towards its center

– One bone may move, both bones may move, or neither bone may move

-A parallel to the muscle fibers

-Determines the muscle action (direction of movement)

-A muscle’s line of pull is relative to the joint it crosses

– Easy to determine the line of pull & resultant muscle action if the muscle fibers run in straight line from origin to insertion in a cardinal plane

*Not the case with pulleys

– Sometimes a muscle (or its tendon) is bent by a pulley or boney prominence as it crosses a second joint
– If so, then the direction of pull is towards the MIDDLE of the “bend”

– Sometimes a muscle crosses more than two joints necessitating many pulleys
– If so, the line of pull is UNIQUE TO EACH JOINT

– A muscle’s “line of pull” may also run in an OBLIQUE PLANE

*No specific names exist for oblique plane movements

-The resulting movement is broke down into its cardinal plane actions

Ex: Coracobrachialis
– It does a shoulder flexion (sagittal plane) & shoulder adduction (frontal plane)

If a muscle has more than one line of pull, it is possible that the motor units one one side of the muscle (but not the other) will be directed to contract

Ex: Shoulder shrug
– Only the motor units of the upper trapezius are directed (by the CNS) to contract

– Deltoid:
– Anterior head: should flexion
– Posterior head: horizontal abduction, shoulder extension
– Lateral head: shoulder abduction

An arrow drawn to depict the muscle’s line of pull

-Represent force & indicates movement

*Can be drawn for all muscle lines of pull
– Includes oblique (diagonal) pull

-Drawn from one attachment to the other attachment
– Aids to illustrate the action of the muscle
– Allows us to “visualize” it
– Arrow shows direction of force
– Length shows magnitude of force (how far muscle contracts)

A diagoal vector to determine its component vectors
– Start: tail
– End: arrowhead

-Resulting component vectors show the cardinal plane actions of the muscle

The force of gravity o the body or an object is constant

Magnitude: always constant, thus always draw the vector to the earth

In order to create movement:
1. The EFFORT FORCE (force attempting to cause movement) must overcome the RESISTANCE (force that opposing movement)

2. Leverage = term to describe MECHANICAL ADVANTAGE that a force can have when moving an object
– Mechanical advantage: ease of being able to move heavy objects with less effort

Term to describe MECHANICAL ADVANTAGE that a force can have when moving an object

*Longer lever arm = less effort to move the lever = less effort to move the load = GREATER leverage

*When we have GREATER LEVERAGE, we have MECHANICAL ADVANTAGE (less effort needed to move something heavy)

Ease of being able to move heavy objects with less effort

Essentially a rigid structure
– Movement of a lever occurs at an AXIS OF MOTION

Distance from the axis to the point of application of force

– A BONE acts as a LEVER
– A JOINT acts as the AXIS
– Muscles create the forces to move the lever

– Leverage of muscle increases when its attachment it located farther from the joint

1. The application of FORCE (effort)

2. The RESISTANCE (load)

3. The AXIS OF MOTION

Force for motion and Resistance to motion re on OPPOSITE SIDES with the Axis in the middle

– Distance of Force and Resistance from the Axis of Motion is not specified (it could change)

– Ex: Seesaw
– Ex: Neck: axis in center; muscle flexing in one direction which is opposite of gravity, but the center part is axis. Weight od head is against gravity
– Triceps: force = contraction in your arm; axis is elbow joint; resistance is against gravity and weight of arm

Force for motion and Resistance to motion are on the SAME SIDE with Axis at one end

– Force (effort) causing motion is FARTHER FROM the axis than the force of Resistance (load)

– Inherently had greater leverage for strength

Ex: Wheelbarrow

Ex: Going on toes: Force effort = soleous muscle; resistance = arch of foot; axis = ball of foot

Force for motion and Resistance to motion are on the SAME SIDE with Axis at one end

-Force (effort) causing motion is CLOSER TO the axis than the force of Resistance (load)

-Inherently has LESS leverage for strength

Ex: Chopsticks

Ex: Lifting weight: Axis = shoulder (because that’s where origin of bicep is); Effort force = elbow; Load = weight

– Caused by rotary forces
– During most movements in the body, muscle contraction causes rotation of a joint

– Movement of body part around an axis = Axial (rotary) joint movement
– Direction of a muscle force determined by the line of pull

*Just like a door, if one side of an object is fixed, then application of a force to that object will cause object to rotate

Page 62,63, 64, 66, 67, 68,69,70

The tendency of a force to rotate an object about an axis
– It depends upon:
– Amount of fore applied
– Distance between the force & its pivot point
-Is a rotary force
– Torque can be CREATED by the muscle, gravity, etc.

– IMAGINARY LINE drawn perpendicular from axis (joint) to the line of force (muscle pull or insertion)

– The perpendicular distance from an axis to the line of action of a force

*What helps us determine how much torque is occurring about the axis (the principle of leverage)

****Longer moment (lever) arm = greater torque at the axis
*****Greater torque = greater tendency of the muscle force to be able to rotate the bone at the joint

Torque = Force x Moment arm

(T = F x M)

In a joint, the pivot is the same as the joint AXIS OF ROTATION

center of mass (COM) and Bass of Support (BOS)

Region bounded by body parts in contact with a support surface

Intersection of the three planes

*The point at which the mass of a person is concentrated, i.e., the “balance point”