In order to produce a locomotor pattern, or maintain joint stability during standing, sufficient joint moments must be generated over an appropriate time period. The moment required about the joint is determined by environmental factors such as movement speed, gravitational forces, and ground reaction forces. Joint moments may be quantified by modeling the segments as a system of rigid links and using principles of inverse dynamics (Bresler and Frankel, 1950). Using this approach, a generalized muscle moment (GMM), the sum of all active and passive tissues acting about the joint may be determined (Hoy et al., 1985). The contribution of individual muscles to the GMM may be determined using tendon transducers, implanted in freely moving animals (Walmsley et al., 1978; Gregor et al., 1988; Fowler et al., 1988) . The purpose of this study was to quantify the relative contribution of individual muscles to the GMM, acting about the cat ankle joint, during locomotion. Peak MG, and LG moments increased as a function of peak ankle GMM during level locomotion (p<.05). Sample sizes within each cat were not sufficient to perform statistical analyses for peak SOL and PLT moments; however, peak PLT moments appeared to increase as a function of peak ankle GMM, while peak SOL moment remained relatively constant. These results indicate that changes in peak ankle GMM were due to increased force output in multiarticular extensor muscles. Changes in the ankle GMM-time integral appeared related to changes in SOL and PLT moment-time integrals, or impulses. A significant relationship was not found between MG or LG muscle moment impulse (p=NS). Roles of these individual muscles are supported by their respective architecture, uniarticular versus multiarticular functions, and physiological make-up.