Concentric vs. Eccentric Muscle Contractions

A muscle has two actions referred to as concentric and eccentric contractions. A concentric contraction occurs when the actin and myosin filaments slide over each other through a motion of their cross-linking connections to provide an increase in the overlap resulting in a shortening of the contractile unit. This shortening of every unit of the total length and width of the muscle results in a movement of the human joint through its full range of motion. A great example is the shortening of the biceps muscle when performing a biceps curl and another the shortening of the hamstring muscles in the back of the thigh to bend the knee.















An eccentric contraction is a lengthening of the muscle under load. Lengthening then occurs through the application of forces sufficient enough to pull the cross-links apart and return the contractile unit to its normal resting overlap. Applied forces come in the following three forms:

By the weight of the individual body part moving with the assistance of gravity.

The action of the muscle opposing the prime mover as the triceps straightening of the elbow.

Resistance as that provided by a free weight, strengthening equipment, or a resistance band.

It is during this motion that the actin and myosin filaments are strained leading to a condition referred to as delayed onset muscle soreness or DMOS. DMOS will usually subside within a day or two as the body adapts to the greater load and is a natural occurrence with any fitness program.

There is, however, an increased risk of injury to the joint and surrounding tissues during the eccentric phase if the motions performed at too great a speed with increased resistance. The muscles should have enough strength and flexibility to combat this increase in force if attempting this form of exercise. I always suggest my clients perform all plyometric exercises without additional resistance for this reason. I also feel that no one should walk or run while carrying weights in the hands or wearing them on their legs secondary to altering their normal gait pattern and increasing the risk of injury to the lower back.