Abstract:Abstract : Muscle mass and strength are well known to decline in response to actual and simulated microgravity exposure. Until now, the mechanism of muscle atrophy under microgravity is still unclear and there is no specific medical intervention. The review examines the effects and mechanisms of actual and simulated microgravity on muscle wet weight, muscle fiber cross-sectional area, muscle fiber type, muscle ultrastructural changes, and adaptive changes in muscle spindle, which is to summarize the major effects of space travel or simulated microgravity on skeletal muscle atrophy.