Chemical and Mechanical Changes during Stretching of Activated Frog Skeletal Muscle

The type of contraction that is performed by an active muscle depends on the mechanical conditions imposed on it; it can develop tension if it is held at a constant length, which is the isometric condition, or it can shorten or be stretched. These conditions are all “physiological” in that all of them are involved in the movements of the body. Stretching of active muscle, which we have studied, is a prominent feature of movements such as climbing down stairs or lowering an object with the arms.