We all know that there are three basic types of muscular contractions: concentric, eccentric and isometric. The first two are utilized daily by lifters seeking bigger, stronger muscles. The third kind, isometric, is kind of like the redheaded stepchild you leave locked in the attic when you have friends over. Only this overplayed clichéd stepchild holds the key to bigger, stronger muscles. Maybe you should consider letting him out more often?
Concentric contraction is a muscular contraction occurring in conjunction with a shortening of the muscle. The bicep is concentrically contracted during the up phase of a bicep curl. The eccentric contraction is defined as a muscular contraction with a simultaneous lengthening of the muscle. This can be seen when lowering the dumbbell during a bicep curl.
The third type of contraction, isometric, is a muscular contraction with the muscle in a static position – no lengthening or shortening. An example of this would be your quads contracting during a wall sit.
While concentric and eccentric contractions should be your bread and butter and account for most of your workload, adding in some isometric exercises can help you break through those pesky sticking points and reach your lifting goals.