The velocity at which a muscle contracts significantly affects the tension that the muscle produces and subsequently affects muscular strength and power. The velocity of exercise is frequently manipulated in a resistance training program to prepare the patient for a variety of functional activities that occur across a range of slow to fast velocities.

Force-Velocity Relationship

The force-velocity relationship is different during concentric and eccentric muscle contractions

Concentric Muscle Contraction

As the velocity of muscle shortening increases, the force the muscle can generate decreases. EMG activity and torque decrease as a muscle shortens at faster contractile velocities, possibly because the muscle may not have sufficient time to develop peak tension.

Eccentric Muscle Contraction

Findings are less consistent for eccentric than concentric muscle actions. During an eccentric contraction, as the velocity of active muscle lengthening increases, force production in the muscle initially also increases but then quickly levels off. The initial increase in force production may be a protective response of the muscle when it is first overloaded. It is thought that this increase may be important for shock absorption or rapid deceleration of a limb during quick changes of direction. The rise in tension may also be caused by stretch of the non-contractile tissue in muscle. In contrast, other research indicates that eccentric force production is essentially unaffected by velocity and remains constant at slow and fast velocities.

Application to Resistance Training

A range of slow to fast exercise velocities has a place in an exercise program. Resistance training with free weights is safe and effective only at slow to medium velocities of limb movement so the patient can maintain control of the moving weight. Because many functional activities involve reasonably fast velocities of limb movement, training at only slow velocities is inadequate. The development of the isokinetic dynamometer during the late 1960s gave clinicians a tool to implement resistance training at fast as well as slow velocities. In recent years, some variable-resistance exercise units (pneumatic and hydraulic) as well as elastic resistance products also have afforded additional options for safely training at fast velocities.

Speed-specific training is fundamental to a successful rehabilitation program. Results of numerous studies since the 1970s have shown that training-induced strength gains in a resistance exercise program primarily occur at the training speeds, with limited transfer of training (physiological overflow) to other speeds of movement. Accordingly, training velocities for resistance exercises should be geared to match or approach the demands of the desired functional activities.

Isokinetic training, using velocity spectrum rehabilitation regimens, and plyometric training, also known as stretch-shortening drills, often emphasize high-speed training.

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