Elastic Energy Stores in Running Vertebrates

Large mammals save much of the energy they would otherwise need for running by means of elastic structures in their legs. Kinetic and potential energy, lost at one stage of a stride, is stored temporarily as elastic strain energy and returned later in an elastic recoil. At high speeds, men and kangaroos seem to save in this way more than half the metabolic energy they would otherwise need for locomotion. It is shown by means of a generalized model that muscles and tendons could both be important as elastic energy stores. Analysis of films and force records of kangaroos hopping shows that strain energy stored while the feet are on the ground must be stored mainly distal to the knee. The principal muscles there have short fibres, and most of the storage must be in tendons. Investigation of camels shows that tendons in the feet, distal to the ankle and wrist, are especially important. The scope for elastic storage while the feet are off the groundis also considered. Though the evidence presented in this paper comes mainly from a few species, the conclusions presumably apply to large mammals in general.