A muscle's length-tension curve illustrates how its force comes from two sources:

Active tension derives from the interaction between myosin and actin active tension.

Passive tension can develop in the muscle's complex connective tissue.

Length-tension curves appear in other forms, including force-angle curves and stress-strain curves. All the curves share the same characteristic shape, because the variables graphed on the x and y axes are just scaled versions of length and force.

Stress-strain curves: Stress, a measure of force per area, replaces force on the y-axis. Strain, an expression of the percentage of elongation beyond resting length, replaces absolute length on the x-axis.

Force-angle curves: Joint angle replaces length as the x-axis variable. To use a flexor muscle group as an example, flexors are short when the joint is flexed and elongated when the joint is extended.

Moment-angle curves: As long as a muscle's moment arm is relatively constant throughout the range of motion of the joint that the muscle crosses, then the muscle's moment-angle curve has a shape that is similar to that of its force-angle curve.

Last updated 1-5-01 ©Dave Thompson PT
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