Muscle Isokinetic Exercise

An isokinetic exercise involves a muscle contraction in which the length of the muscle is changing while the contraction is performed at a constant velocity. In theory, maximal resistance is provided throughout the range of motion by the machine. The resistance provided by the machine will move only at some preset speed regardless of the force applied to it by the individual. Thus the key to isokinetic exercise is not the resistance but the speed at which resistance can be moved.

Several isokinetic devices are available commercially; Cybex, Biodex, Kin - Com, and Lido are among the more common isokinetic machines. In general, they rely on hydraulic, pneumatic, and mechanical pressure systems to produce constant velocity of motion. The majority of the isokinetic devices are capable of resisting both concentric and eccentric contractions at a fixed speed to exercise a muscle. A major disadvantage of these units is their cost. Many of them come with a computer and printing device and are used primarily as diagnostic and rehabilitative tools in the treatment of various injuries.

Isokinetic devices are designed so that regardless of the amount of force applied against a resistance, it can be moved only at a certain speed. That speed will be the same whether maximal force or only half the maximal force is applied. Consequently, when training isokinetically, it is absolutely necessary to exert as much force against the resistance as possible (maximal effort) for maximal strength gains to occur. This is one of the major problems with isokinetic strength - training program.

Anyone who has been involved in a weight - training program knows that on some days it is difficult to find the motivation to work out. Because isokinetic training requires a maximal effort, it is easy to "cheat" and not go through the workout at a high level of intensity. In a progressive resistive exercise program, one knows how much weight has to be lifted with how many repetitions. Thus isokinetic training is often more effective if a partner system is used primarily as a means of motivation toward a maximal effort.

When isokinetic training is done properly with a maximal effort, it is theoretically possible that maximal strength gains are best achieved through the isokinetic, training method in which the velocity and force of the resistance are equal throughout the range of motion. However, there is no conclusive research to support this theory. Whether changing force capability is in fact a deterrent to improving the ability to generate force against some resistance is debatable. In the athletic training setting, isokinetics are perhaps best used as a rehabilitative and diagnostic tool rather than as a training device.
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