Effects of spaceflight, simulated spaceflight and countermeasures on single muscle fiber physiology.

Since the first human flew in space in 1961, there has been extensive scientific interest in the responses of the human body and how it adapts to this unique environment. From the available data, it appears that all major systems in the human body undergo an adaptive change while in a microgravity environment. In particular the human muscle system appears to undergo loss of muscle mass and strength which greatly influences the maximal work capacity of the muscle. Recently, our research group has been involved in a series of whole muscle and cellular studies during periods of short duration space flight, bed rest, and unilateral lower limb suspension (ULLS) in an attempt to elucidate the changes that are occurring in the whole muscle and single muscle fiber contractile properties with unloading. In addition, various countermeasure activities for skeletal muscle have been part of the space flights and ground-based studies. The intention of this paper will be to briefly review our findings in whole muscle, cellular, and countermeasure effectiveness with human muscle.