To date, the medium and long-term space flight is urgent in need and has become a major task of our manned space flight program. There is no doubt that medium and long-term space flight has serious damaging impact upon human physiological systems. For instance, atrophy of the lower limb anti-gravity muscle can be induced during the space flight. Muscle atrophy significantly affects the flight of astronauts in space. Most importantly, it influences the precise manipulation of the astronauts and their response capacity to emergencies on returning to the atmosphere from space. Muscle atrophy caused by weightlessness may also seriously disrupt the normal life and ＇work of the astronauts during the re-adaptation period. Here we summarize the corresponding research concentrating on weightlessness-induced changes of muscular structure and function. By combining research on muscle pain, which is a common clinical pain disease, we further provide a hypothesis concerning a dynamic feedback model of ＂weightlessness condition → muscular atrophy ←→ muscle pain＂. This may be useful to explore the neural mechanisms underlying the occurrence and development of muscular atrophy and muscle pain, through the key study of muscle spindle, and furthermore provide more effective therapy for clinical treatment.
