Tuesday, February 4, 2014

Muscle Force - Velocity Relationship

Previously, I discussed how muscle force is dependent on the length of the muscle.

Now I want to talk briefly about maximum muscle force is dependent on muscle contraction velocity. As seen in the figure below, maximum muscle force is inversely proportional to the contraction velocity. When a muscle is contracted very rapidly, much less force can be generated than if the muscle is contracted isometrically (no muscle shortening).

Conversely, peak force increases above isometric max if the muscle is stretched while contracted for small stretching velocities before topping out.

Why does the maximum possible force decrease? It has to do with the actin-myosin cross-bridges which form the foundation of a contraction. The cross-bridges are increasingly unable to reattach to continue to aid in muscle contraction. The less cross-bridges, the less tension the muscle can produce.

Why does this matter? Biomechanical engineering of devices and analysis of movement is dependent on understanding this concept. You don't want to place yourself in a context that has you trying to generate forces to inefficiently.

from http://wweb.uta.edu/faculty/ricard/Images/Force-Velocity.gif