Abstract
This study reports the effects of 18 d space flight (STS-78) on quadricep muscle function. Four astronauts were examined 2 wks prior to launch and 2 d after landing. Maximal voluntary isometric force (MVC) and electromyographic(EMG) activity, using surface electrode technique, were measured during knee extension. Also, EMG activity was measured during a 60 sec sustained isometric action at 40% MVC. Results showed a 10% decrease (p<0.05) in MVC, accompanied by a decrease (p<0.05) in EMG activity. Over-all EMG activity at 40% MVC increased (p<0.05) and the rate of increase in EMG over 60 sec was greater after space flight. These results suggest a marked impairment in muscle function in response to 18 d space flight. Although this effect in large part, can be attributed to muscle atrophy, it appears that a decrease in neural drive is also responsible for the decrease in maximal voluntary force. In addition, the present result suggest that space flight increases fatigability of unloaded skeletal muscle.
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