Our exercise sessions typically involve isotonic and isometric muscle actions.  During an isotonic muscle action, the agonist (prime mover) contracts (or shortens) as the antagonist relaxes (or lengthens).  For example, when you bend your arm, the Biceps Brachii shortens and the Triceps Brachii lengthens.  During an isometric muscle action,  there is no visible change in muscle length as the muscles involved stabilize the body and place very little stress on the body’s joints.  For example, when you perform a squat, the adductors and abductors (inner and outer thigh muscles) stabilize your legs, minimizing side motion.

Differing  from isotonic and isometric muscle actions, an isokinetic muscle action does not involve movement.  The speed of movement is stable, and resistance varies when force is produced.  This type of training requires expensive equipment used in rehabilitation or exercise physiology laboratories, which measure the amount of force produced by the muscles and changes the resistance in order for the speed of movement to remain constant, no matter how much force is exerted.  When you use this machine (dynamometer), you will feel more resistance as you push or pull harder.  For instance, if you push hard against the machine it will provide a lot of resistance whereas if you push gently the machine will decrease load.   Isokinetic training improves strength, endurance, and neuromuscular efficiency because the muscular tension is maximized during the entire range of motion.

If you want to learn more about isokinetic training, you can ask a certified personal trainer at your local gym.  To try isokinetic training, please visit a local rehabilitation clinic.  Or, the simplest way to try isokinetic training is swimming!  The water provides resistance:  When you move slowly through the water, the water provides little resistance and you expend minimal energy whereas when you move quickly through the water, the water provides more resistance and you use more energy.  Thereby, swimming is an isokinetic exercise.

References

Clark, M. A., Lucett, S.C., & Sutton, B.G. (2012).  NASM Essentials of Personal Fitness Training, 4 ed.  Baltimore, MD:  Lippincott Williams & Wilkins.

CSMI (2013, April 21).  All about isokinetics [Web log post].  Retrieved from http://www.isokinetics.net/isokinetics/definitions/what-is-isokinetic.htm.