HURTT, B.C.*; BEKOFF, A.C. : MODULATION OF THE WALKING MOTOR PATTERN IN CHICKS DUE TO ASYMMETRIC LOADING OF THE FLEXOR MUSCLES

Rhythmic motor patterns, such as walking, can be characterized by various components of the movement cycle using a variety of techniques, including kinematic and electromyographic (EMG) analyses. Normal, unloaded walking motor patterns are asymmetric: extension duration is longer than flexion, and extensors are active for a greater percentage of the cycle period than flexors. One significant question of interest concerns the role sensory input plays in establishing and modulating various rhythmic motor patterns such as walking. Specifically, we were interested in examining the changes in walking motor output in chicks following loading, and subsequent unloading, of the legs with weights. Eight day old chicks walked under three conditions: without weights for 10 minutes (PRE), with small, 8 gram leg weights placed below each ankle for 10 minutes (WTS), and after removal of the weights for 10 minutes (POST). Kinematic markers were placed at five points and digitized to determine joint movement at the three major leg joints: hip, knee and ankle. EMG analysis was conducted by implanting electrodes in antagonistic muscles at each of the three major leg joints. The WTS condition resulted in an increase in extension (stance) as well as alterations in the characteristics of stance, while flexion decreased. In response to the increased load, both extensor and flexor activity increased in duration, resulting in an overlap of antagonist bursts. The POST condition did not show a complete recovery to the normal walking, or PRE, level by either kinematic or EMG measures. Rather, it indicated a progressive but incomplete recovery of normal walking at 10 minutes. In all three conditions, extension remained highly correlated with cycle period. However, flexion and flexor activity became more highly correlated with cycle period during WTS and POST.