EFFECT OF HINDLIMB UNLOADING ON LOCOMOTOR STRATEGY DURING TREADMILL LOCOMOTION IN THE RAT

Electromyographic activity (EMG) was recorded from the soleus muscles of adult rats during treadmill locomotion after 7 and 14 days of hindl imb unloading, and after 7 days of recovery. Observation of the rats i ndicated that treadmill locomotion was disrupted after unloading since the animals had some difficulty in moving. Soleus muscle EMC analysis was performed. Onset and offset of bursts of activity were determined , and the relationships between step duration and cycle duration were analysed. Our main results were as follows: firstly, mean cycle durati on was increased after 14 days of hindlimb unloading when walking at l ow speed. At high speed, no difference was observed. Secondly, linear regression analysis indicated that the relationships between step dura tion and cycle duration were altered after 7 days of unloading. Thirdl y, adaptation occurred, since the normal slope and correlation coeffic ient were restored after 14 days of unloading. Fourthly, when speed in creased, no variation of mean EMG was demonstrated after hindlimb unlo ading whereas an increase occurred in normal rats. Fifthly, video anal ysis showed that the rats presented frequent hyperextension of the hin dlimb after unloading. These abnormal steps were more numerous when wa lking at low speed. These data would indicate that a transitory disrup tion of the soleus muscle motor pattern occurred after 7 days of unloa ding. This disruption depended on the treadmill belt speed. Possible o rigins of these modifications are discussed.