Torque

static equilibrium

- the sum of all forces are equal to zero

- the sum of all torques are equal to zero

what can we do with a free body diaphragm

- to determine how much muscle force is required by a joint to hold a position

- to determine the magnitude of the joint reaction force during the same activity

steps of a free body diaphragm

- identify and isolate the free body under consideration

- establish a coordinate reference frame: x is parallel with the body segment of interest, y axis is determine by the right hand rule

- draw the internal ( muscular) and external forces that act on the system

- draw the joint reaction force

vector composition

- adding forces together

- tip to tail or polygon method

vector resolution

- a resultant vector gets "decomposed" into two forces

rotatory component

- also known as (y)

- perpendicular to the long axis of the moving segment

translatory component

- also known as (x)

- parallel along the axis of the moving segment

- is it compressive or distractive

force

- can change the magnitude of torque

- not the only factor that can do so

moment arm

- perpendicular distance between the line of force and axis of rotation

torque units

(Newton-meters) or (inch-pound)

how can we use torque to understand joint mechanics

- use trigonometry to solve for muscle force

- use vector decomposition to determine rotatory and translatory components

- use vector addition to solve for Joint Reaction Forces

- starting with assuming all forces and torques are = 0

trigonometry review

- sin: opp/hyp

- cos: adj/hyp

- tan: opp/adj

how the joint position affects the internal torque

- method 1: multiple the rotatory force x IMA

how the joint position affects the external torque

-method 1: multiply the rotatory force * EMA or IMA

- EMA: distance from axis to the external force

- method 2: multiply the force * moment arm for that force

why use method 2

- to estimate relative torque potential based on the moment arm