ALLOMETRY OF MUSCLE, TENDON, AND ELASTIC ENERGY-STORAGE CAPACITY IN MAMMALS

This paper considers the structural properties of muscle-tendon units in the hindlimbs of mammals as a function of body mass. Morphometric a nalysis of the ankle extensors, digital flexors, and digital extensors from 35 quadrupedal species, ranging in body mass from 0.04 to 545 kg , was carried out. Tendon dimensions scale nearly isometrically, as do es muscle mass. The negative allometry of muscle fiber length results in positive allometric scaling of muscle cross-sectional areas in all but digital extensors. Maximum muscle forces are predicted to increase allometrically, with mass exponents as high as 0.91 in the plantaris, but nearly isometrically (0.69) in the digital extensors. Thus the ma ximum amount of stress a tendon may experience in vivo, as indicated b y the ratio of muscle and tendon cross-sectional areas, increases with body mass in digital flexors and ankle extensors. Consequently, the c apacity for elastic energy storage scales with positive allometry in t hese tendons but is isometric in the digital extensors, which probably do not function as springs in normal locomotion. These results sugges t that the springlike tendons of large mammals can potentially store m ore elastic strain energy than those of smaller mammals because their disproportionately stronger muscles can impose higher tendon stresses.