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.