KINS 3522 unit 2 moments

torques

the turning effect produced by a force

also called a moment

think of it as an angular or rotary force

directly proportional to the magnitude of force as well as the distance between the line of action of the force and the axis of rotation

torque part 2

motion of a restrained system

has an axis of rotation

one side is fixed in space

force is applied away from the axis

line of action is not through the axis

force includes what in torque

• magnitude

• point of application

• direction

• line of action

moment arm

perpendicular distance between line of action of force and axis of rotation

counterclockwise is

positive

clockwise is

negative

equation for torque

force x moment arm

F x d perpendicular

another way to calculate torque

break resultant force into component parts

find perpendicular component of force

moment arm

shortest distance between the axis of rotation and line of action of the force

perpendicular to the force’s line of action and axis of rotation

lever arm

distance between the point of force application and the axis of rotation

perpendicular component of force is used for

torque calculation when you do not have the moment arm

when there is moment arm

T= F x d perpendicular

lever arm equation

T= force perpendicular x d

torque in humans

muscle attach at some distance away from joint center of rotation

therefore, all muscles produce torque about the joints they cross

center of mass

point around which mass or weight is considered to be concentrated

‘balance point of the body”

the weights are balanced, creating equal torques on either side of the fulcrum. EQUILIBRIUM

aka center of gravity

center of mass cont

serves an index of total body motion

track the COG during motion

may be in reference to whole body or individual segments (% of body height or % of segment length)

location determines the way the body responded to external forces

magnitude of torque

muscle contributions (internal moment)

muscle force (tension)

muscle lever arm

muscle force > net joint torque > motion

concentric muscle action

muscle internal moment and motion same direction

eccentric muscle action

muscle internal moment and motion opposite direction

rotary component

perpendicular to body segment

created internal moment

causes motion

non rotary component

perpendicular to rotary component, parallel to bones

does not contribute to internal moment

causes joint compression or distraction (stabilization or dislocation)

muscle force components

joint position influences the magnitude and direction of muscle force components

angle formed by line of action and bony segment influences magnitude of rotary and non rotary components

How does changing joint position influence internal joint moment & the effects of the non-rotary component?

90 degrees highest torque produced

the internal moment created by muscle depends on three things

1. muscle force (F)

2. lever arm (d)

3. angle of pull (theta)

muscle contributions (net internal moment)

muscles may produce co contraction

creates opposing joint torques (opposite direction)

motion occurs in direction of this _______

agonist of knee extension

quads

antagonist of knee extension

hamstrings

what is the purpose of antagonist muscle co contraction

• control velocity of joint motion

• increase stability at joint

what type of contraction are the muscles producing in knee flexion

• quadriceps > concentric contraction

• hamstrings > eccentric contraction

non muscle contributions (external moment)

segment mass will cause a joint moment

any external object attached or held by segment will produce a joint moment

ground reaction forces

internal and external moments

IF x D= EF x D1

name the moment

4 words

first word internal or external

second word joint (elbow, knee)

third word: direction of motion (flexion)

fourth word moment

external moment

a moment caused by forces acting external to the body/segment that causes moments/torques across a joint axis.
– Think something that causes a segment or joint to move!
– An example of an external moment would be a moment caused by the force between the plantar foot and the ground, which is called ground reaction force (GRF)

internal moment

a moment caused by forces acting internally within the body/about the segment that
causes moments/torques across a joint axis.
– Think a muscle that is contracting to either drive the movement of a segment or to control or slow the segments movement

A concentric muscle action is when the muscle internal moment and motion are in _______ directions and is a shortening contraction.

same

An eccentric muscle action is when the muscle internal moment and motion are in __________ directions.

opposite

The rotary muscle force component is perpendicular to the bone segment.

true

Which of the following is NOT a force that can contribute to an external joint moment?

1. Option A

   Biceps

2. Option B

   mass of forearm

3. Option C

   ground reaction force

4. Option D

   dumbbell

option A

biceps

torque is a vector so it has magnitude and direction.

true

The moment arm is the parallel distance between the axis of rotation and the line of action of the force.

false

Torque in the counterclockwise direction is typically defined as positive.

true

what type of moment

external knee flexion moment

what type of moment

external ankle dorsiflexion moment

what type of moment, letter A (bicep muscles)

internal elbow flexion moment

what type of moment, letter B (tricep muscles)

internal elbow extension moment