The mysteries of eccentric muscle action

Muscle actions are typically divided into 3 categories：concentric,isometric,and eccentric.An active muscle that is shortening and produces positive mechanical work is said to work concentrically;an active muscle that is not changing its length,and thus does not produce net work,is said to work isometrically;and an active muscle that is elongated by external forces,and thus absorbs work,or produces negative work,is said to work eccentrically．