Biomechanics Module 2: Torque

Static equilibrium

the sum of all forces are equal to zero

the sum of all torques are equal to zero

What are the two forces a vector resoluton gets decomposed into?

rotatory component

translatory component

Rotatory component

perpendicular to the long axis of the moving segment

translatory component

parallel to the long axis of the moving segment (compressive and distractive)

Moment arm

perpendicular distance between the line of force and axis of rotation (Nm)

Which statement regarding the rotatory component is true?

Perpendicular to the long axis of the moving segment

Torque produced by a 670 N body weight with a 0.20 m moment arm

134 Nm

Where do you place a dynamometer to examine elbow extensors?

Posterior distal forearm

A PT student who is frustrated with their biomechanics homework rests their head on their flexed arm at an angle of 15 degrees. The weight og their head in their hand is 120N and their IMA is 3cm. What is the torque of the system?

0.93 Nm

Which combination increases the torque produced by a muscle?

More muscle force + longer moment arm

When moving from 90° flexion to 45° to 0°, which position generates the greatest external torque from gravity?

90° Flexion

Holding arm extended at 90° with a ball: which direction is the joint reaction force pointing relative to muscle force?

Parallel to the force of the muscle, pointed in the opposite direction of the muscle force

Calculate total external torque at shoulder: arm 25° abducted, length to arm COM = 12" (10 lbs), total length = 20" (4 lbs ball).

84.5"lbs

Which muscle position relative to the humeral head produces torque and rotates the arm?

A muscle that is located along the same plane but not on either axis

Calculate abduction angle: arm length to COM = 9", moment arm = 5".

33.7°