An electromyographic analysis of hindlimb function in Alligator during terrestrial locomotion

The neuromuscular control of the hindlimb of American alligators (Alligator mississippiensis) walking on a treadmill was analyzed using simultaneous electromyography (EMG) and cineradiography. EMG and kinematic data were integrated with myological information to discern the interplay of muscles mediating hip and knee movement during the high walk. Twelve muscles, subdivided into 23 individual heads, cross the hip joint of Alligator. Activity patterns of 12 heads of 11 hip muscles and one knee muscle were recorded and quantified. An additional five heads from four muscles were recorded in single individuals. During the stance phase, the caudofemoralis longus prevents hip flexion and actively shortens to retract the femur through an arc of 60-80°. At the same time, the adductor femoris 1 and pubo-ischio-tibialis control femoral abduction. The knee is extended 30-40° during stance by contraction of the femoro-tibialis internus. These stance phase muscles often produce discontinuous, periodic EMG signals within their normal burst profile. In late stance and early swing, the ilio-fibularis and the pubo-ischio-tibialis are responsible for flexing the knee. The limb is protracted by the pubo-ischio-femoralis internus 2 and pubo-ischio-femoralis externus 2, which flex the hip. The ilio-femoralis abducts the limb during swing to suspend it above the tread. The role of the ambiens 1, which is active in midswing, is unclear. The ilio-tibialis 2, flexor-tibialis externus and flexor-tibialis internus 2 yield sporadic, low amplitude EMGs; these muscles are recruited at a very low level, if at all, during the slow high walk. Although EMGs do not conclusively delineate muscle function, activity patterns are particularly helpful in elucidating the complex interaction of muscular heads in this system. J. Morphol. 234:197-212, 1997. © 1997 Wiley-Liss, Inc.