Within the traditional array of different kinds of muscle contractions, what scientists refer to as isokinetic contractions are very rare. However, when talking about using various fitness machines, many in the fitness industry have begun to refer to isokinetic exercise as a variable resistance type of training.

According to this definition, isokinetic exercise is an exercise that provides a variable resistance to a constant limb movement. These kinds of adaptive exercises require equipment that can quickly accommodate changes in resistance.

One example of an isokinetic exercise is a stationary bike that responds to a constant leg movement by the user. The resistance offered by the stationary bike may vary, while the speed of limb motion and subsequent revolutions per minute stays the same.

Some fitness trainers refer to an active dynamometer which can also provide for isokinetic exercise training. In gyms and health clubs, isokinetic equipment might be present in the form of elastic bands, exertubes or specialized machines.

Because the variable resistance in these types of exercise equipment is so controlled, it helps to prevent a lot of different kinds of injury for users. Isokinetic exercise also offers more direct response and customization of challenges to a body's momentum. This kind of exercise and gear can be especially helpful after injury, where participants want to take care not to strain muscles with excessive resistance.

Traditional types of exercise include isotonic exercise, where tension or resistance remains unchanged. Dumbbells and other free weights are good examples of this kind of exercise, where bicep curls and other movements take place against a static resistance. Isotonic exercises require two specific types of muscle contractions according to the load placed on the body:

• A concentric muscle contraction occurs when the body is able to manipulate a weight load in a certain direction.
• An eccentric muscle contraction occurs when the weight is too much for the body, and the muscles focus on distributing impact, rather than raising or lowering a weight load.

Another kind of conventional training is isometric training. In isometrics, there is no movement, and the muscle length and joint angle do not change. Someone holding free weights while not in motion is an example of this kind of training.

As more adaptive resistance equipment becomes available on a broader scale, fitness experts continue to look at how isokinetic exercise can be useful for specific target audiences, with attention to gender and age. It may be that tomorrow's fitness schedules will include more of this kind of customized activity for fitness participants who can use these adaptive training methods to get muscles prepared for specific athletic and recreational activities.