Responses of Electromyogram Activity in Adductor Longus Muscle of Rats to the Altered Gravity Levels
Abstract
Responses of electromyogram (EMG) activities in the rostral and caudal regions of adductor longus (AL) muscle to altered gravity levels during parabolic flight of a jet airplane, as well as hindlimb suspension, were investigated in adult rats. Tonic EMGs in both regions were noted when the rats were exposed to hyper-G, as well as 1-G. The hip joints were adducted and the sedental quadrupedal position was maintained at these G levels. However, the EMG activities in these regions decreased and became phasic, when the hip joints were abducted and extended backward in μ-G environment. Such changes of joint angles caused passive shortening of sarcomeres only in the caudal region of AL. Atrophy and shift toward fast-twitch type were noted in fibers of the caudal region after 16-day unloading. Although fiber transformation was also induced in the rostral region, no atrophy was seen in fast-twitch fibers. The data may suggest that the atrophy and shift of phenotype caused by gravitational unloading in fibers of the caudal region may be related to the decrease in the neural and mechanical activities. Fiber type transformation toward fast-twitch type may be also related to the change of muscle activity from tonic to phasic patterns, which are the typical characteristics of fast-twitch muscle. However, the responses to unloading in fibers of rostral region were not related to the reduction of mechanical load.
- Publication:
-
Life in Space for Life on Earth
- Pub Date:
- June 2008
- Bibcode:
- 2008ESASP.663E.137O