ALEXANDER, R McN: Tendon Elasticity and Muscle Function

Vertebrate animals exploit the elastic properties of their tendons in several different ways. First, metabolic energy can be saved in cyclic activities if tendons stretch and then recoil, storing and returning elastic strain energy, as the body loses and regains kinetic energy. The leg tendons of medium to large hopping and running mammals save energy in this way, and in some cases their muscle bellies have become rudimentary. This function does not seem to be important in small mammals, in which the tendons have to be thick enough to withstand the relatively large forces of jumping. The elasticity of an aponeurosis in the back saves energy in galloping. The possibility that tendon elasticity may be important in the swimming of dolphins and the flight of birds is also considered. Secondly, tendons can recoil elastically much faster than muscles can shorten, enabling animals to jump further than they otherwise could. Thirdly, tendon elasticity affects the control of muscles, enhancing force control at the expense of position control. Simple mathematical models illustrate the principles involved.