Human Levers

Question 1

Torque

Answer 1

Torque is a force which results in rotation
movements.
Torque equals to the force (F) applied, the length (L) of the lever arm, and the angle between the force vector and the lever arm.

Question 2

Torque - Internal vs External

Answer 2

Internal torque: generated by the muscle
External torque: generated by the mass of the resistance
Internal torque needs to be higher than external torque to produce movement.
Voluntary human movement involves torque generation in the articulations.

Question 3

Point of Force Application

Answer 3

Insertion of tendon of muscle.
The force is represented by the muscle responsible for the movement. It can be either the agonist, or the antagonist. (concentric or eccentric contraction?)

Question 4

Mechanical Advantage

Answer 4

Ratio between the distance from the fulcrum to the point of Force application (effort distance/arm) and the distance between the fulcrum to the point of Resistance application (Resistance distance/arm).
The longer the effort arm is compared to the resistance arm, less force is needed to lift the object.
Benefit of the lever system.

Question 5

Anatomic Pulley

Answer 5

Deflects the action line of the muscle away from the joint axis, increasing the lever/moment arm, generating higher torques for the same force.
Elongates the distance between center of motion and the point of force application. Allows for a more efficient mechanical work of the muscle (e.g. patella increases the lever arm of the knee).

Question 6

Changes in the Moment Arm - Knee Flexion to Extension

Answer 6

From flexion to extension of the knee:
In flexion: Smallest moment arm - resistance arm in line with the center of motion, no moment arm.
In between: Moment arm increases.
In extension: Producing the highest torque, largest moment arm.
Amount of resistance always the same.

Question 7

At what degree of angle of pull (pulley) is the resistance maximal?

Answer 7

Maximal resistance occurs when the angle of pull
of the pulley´s rope is 90° to the extremity being resisted.
• With this pulley arrangement, the greatest resistance is produced at 90° of knee flexion (becomes easier with increasing extension of the knee).

Question 8

Angle of Pull - Free Weights

Answer 8

Maximal resistance occurs when the pull weight is

perpendicular to the ground regardless of the extremity´s position.

Question 9

Levers

Answer 9

A simple machine that contains a rigid bar and a fulcrum.

• Point of force application
• Fulcrum
• Point of resistance

Question 10

Point of Resistance

Answer 10

The resistance represents the mass of the segment(s) being mobilized, and the point of application is the center of mass – any additional load will shift this COM towards the load.

Question 11

Fulcrum

Answer 11

Center of motion.
Pivot.
Always corresponds to the joint axis of the mobilized joint (articulation that is being moved).

Question 12

First-Class Lever

Answer 12

Fulcrum is located between the resistance and force arms.

Question 13

Second-Class Lever

Answer 13

Less common.
Resistance point is between the fulcrum and the
force (e.g. wheelbarrow).

Question 14

Third-Class Lever

Answer 14

Force is between the fulcrum and the resistance.

Most common, especially with OKC exercises.