How muscles function--the work loop technique.

The primary function of muscle is to generate force and produce movement in animals. Before 1985, muscle function had typically been examined under maximally stimulated conditions, while held at a constant length or allowed to shorten at a constant force. Although crucial for understanding fundamental mechanisms and properties of muscle, these contractions at a constant length (isometric) or under a constant load (isotonic) while maximally stimulated are seldom physiologically relevant to an animal.