Type of Muscle Contraction

Three basic types of muscle contraction result from different movements--concentric, eccentric and isometric contractions. Both the concentric and eccentric contractions occur when you move a joint through a range, while the isometric contraction involves no movement. A concentric contraction is one that shortens the muscle. The eccentric contraction, often used when controlling the release of a movement, lengthens the muscle. You can easily see these types of muscular contractions when you perform biceps curls. As you lift the weight toward your shoulder, the biceps shortens concentrically, and when you return your arm to the starting position, releasing the move toward the ground, the biceps works eccentrically. You would perform the biceps curl against an immovable object to create an isometric contraction.

Many rehabilitation experts recommend using isometric resistance if your joint is inflamed, since the joint does not move. Both isotonic (moving) and isometric strengthening routines are effective for individuals with arthritis (Wrightson and Malanga 2001). While isometric routines do improve strength, they are not as effective as resistance programs that use motion. The strengthening benefit from an isometric exercise is primarily for the angle at which the resistance activity is performed, so it is often necessary to do several contractions at different joint angles. Because you are not moving the joint, an isometric exercise does not help you maintain total joint range of motion. Also, an isometric contraction actually reduces blood flow to the muscle, which causes blood pressure to rise.

If a joint is highly inflamed, you can perform brief isometric contractions, with repetitions (Lieberson 1984). This technique limits the blood pressure increase, while still giving the strength benefits. If your joint is not inflamed, I highly recommend doing your resistance moves through as much of the joints range of motion as possible. In this way, you can maintain or even extend that range while reaping the benefits of increased strength.