The generation of force also depends on the velocity of
the movement. This relationship is known as the force–
velocity curve. During concentric muscle actions (when the
muscle shortens), an increase in the velocity of movement
results in lower force. Similarly, muscle actions against
high loads can only performed at relatively slower velocities.
On the other hand, during eccentric muscle actions
(when the muscle is lengthening), an increase in velocity
results in higher force. This is the reason why strengthening
exercises that include eccentric muscle actions are frequently
and effectively used during the rehabilitation of
musculoskeletal injuries. Finally, the power produced by
an active muscle depends on the force generated (power–
force curve) and the velocity of movement (power–velocity
curve). Power is low at low forces and increases to a
maximal level at approximately 40 % of the maximal
force. On the other hand, power is low at slow velocities
and increases to a maximum that depends on the muscle
fiber type (see above) and is approximately 15–20 % of the
maximal velocity.