FORMS OF FORWARD QUADRUPEDAL LOCOMOTION - III - A COMPARISON OF POSTURE, HINDLIMB KINEMATICS, AND MOTOR PATTERNS FOR DOWNSLOPE AND LEVEL WALKING

To gain further insight into the neural mechanisms for different forms of quadrupedal walking, data on postural orientation, hindlimb kinema tics, and motor patterns were assessed for four grades of downslope wa lking, from 25% (14 degrees slope) to 100% (45 degrees), and compared with data from level and downslope walking at five grades (5-25%) on t he treadmill (0.6 m/s). Kinematic data were obtained by digitizing cin e film, and electromyograms (EMGs) synchronized with kinematic records were taken from 13 different hindlimb muscles. At grades from 25 to 7 5%, cycle periods were similar, but at the steepest grade the cycle wa s shorter because of a reduced stance phase. Paw-contact sequences at all grades were consistent with lateral-sequence walking, but pace wal king often occurred at the steepest grades. The cats crouched at the s teeper grades, and crouching was associated with changes in fore-and h indlimb orientation that were consistent with increasing braking force s and decreasing propulsive forces during stance. The average ranges o f motion at the hindlimb joints, except at the hip, were often differe nt at the two steepest slopes. During swing, the range of knee- and an kle-joint flexion decreased, and the range and duration of extension i ncreased at the ankle joint to lower the paw downward for contact. Dur ing stance the range of flexion during yield increased at the ankle jo int, and the range of extension decreased at the knee and metatarsopha langeal joints. Downslope walking was also associated with EMG changes for several muscles. The hip extensors were not active during stance; instead, hip flexors were active, presumably to slow the rate of hip extension. Although ankle extensors were active during stance, their b urst durations were truncated and centered around paw contact. Ankle f lexors were active after midstance at the steeper slopes before the ne ed to initiate swing, whereas flexor and extensor digit muscles were c oactive throughout stance. Overall the changes in posture, hindlimb ki nematics, and activity patterns of hindlimb muscles during stance refl ected a need to counteract external forces that would accelerate angul ar displacements at some joints. Implications of these changes are dis cussed by using current models for the neural control of walking.