Eccentric Contractions.

An eccentric contraction is where a muscle is forced to lengthen while trying to shorten. That is the muscle is being used as a brake, absorbing energy, or doing negative work. Examples for the quadriceps or knee extensors include walking down hill, skiing, horse riding, but not cycling, rowing or swimming, where the muscles are not used as brakes. By contrast, a concentric contraction involves a muscle shortening while active, delivering energy, doing positive work, and acting as an engine. Isometric contraction involves developing tension with no movement, supporting a load, and doing zero work.

Eccentric contractions lead to many difficult to explain results, both in studies of muscle, and in everyday life. Consideration of these results led to the formulation of the "popping sarcomere hypothesis" in 1990, which has provided a focus for ongoing research.

The puzzling results

The basic hypothesis

Extension to eccentric exercise

Predictions of the theory

Testing of the predictions

Applications