Electromyographic activity in the Rhesus monkey forelimb muscles during a goal directed movement and locomotion...

The aim of the present study was to analyse the effects of microgravity on i) the achievement of goal-directed arm movements and ii) the quadrupedal non-human primate locomotion. A reaching movement in weightlessness would require less muscle contraction since there is no need to oppose gravity. Consequently the electromyographic (EMG) activity of the monkey forelimb muscles should be changed during or after spaceflight. EMG activity of the biceps and triceps muscles during goal-directed arm movements were studied in Rhesus monkeys before, during and after 14 days of spaceflight and flight simulation at normal gravity. The EMG activity was also recorded during treadmill locomotion before and after spaceflight. When performing arm motor tasks, the delay values of the EMG bursts were unchanged during the flight. On the contrary, mean EMG was significantly decreased during the flight comparatively to the pre- and post-flight values, which were very similar. Compared with flight animals, the control ground monkey showed no change in the burst durations and mean EMG. After spaceflight, quadrupedal locomotion was modified. The animals had some difficulty in moving, and abnormal steps were numerous. The integrated area of triceps bursts was increased for the stance phase during locomotion. Taken together these data showed that spaceflight induces a dual adaptative process: first, the discharge of the motor pools of the forelimb musculature was modified during exposure to microgravity, and then upon return to Earth, monkeys changed their new motor strategy and re-adapt to normal gravity.