AN ELECTROMYOGRAPHIC ANALYSIS OF HINDLIMB FUNCTION IN ALLIGATOR DURING TERRESTRIAL LOCOMOTION

The neuromuscular control of the hindlimb of American alligators (Alli gator mississippiensis) walking on a treadmill was analyzed using simu ltaneous electromyography (EMG) and cineradiography. EMG and kinematic data were integrated with myological information to discern the inter play of muscles mediating hip and knee movement during the high walk. Twelve muscles, subdivided into 23 individual heads, cross the hip joi nt of Alligator. Activity patterns of 12 heads of 11 hip muscles and o ne knee muscle were recorded and quantified. An additional five heads from four muscles were recorded in single individuals. During the stan ce phase, the caudofemoralis longus prevents hip flexion and actively shortens to retract the femur through an are of 60-80 degrees. At the same time, the adductor femoris 1 and pubo-ischio-tibialis control fem oral abduction. The knee is extended 30-40 degrees during stance by co ntraction 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 lim b is protracted by the pubo-ischio-femoralis internus 2 and pubo-ischi o-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 spora dic, low amplitude EMGs; these muscles are recruited at a very low lev el, if at all, during the slow high walk. Although EMGs do not conclus ively delineate muscle function, activity patterns are particularly he lpful in elucidating the complex interaction of muscular heads in this system. (C) 1997 Wiley-Liss, Inc.