Muscular deconditioning after long exposure to microgravity could interfere with the safe completion of critical tasks during space flight or during emergency or routine landing or egress. The objective of this study was to evaluate changes in the strength of the arm muscles after space flight and to determine whether extravehicular activity during flight affects those changes.
Before and after space flights of 9 to 14 days, the strength of the arm muscles of three astronauts who performed extravehicular activities during flight and one who did not was assessed. The muscles that act on the elbow and the muscles that turn the forearm and wrist were tested with LIDO isokinetic dynamometers. These dynamometers provide variable resistance so that movements continue at the same speed (i.e., they are isokinetic) regardless of the force applied. Both concentric and eccentric strength were measured. Concentric strength is the strength of a muscle as it contracts to move a body part, while eccentric strength is the strength of the muscle as it is gradually lengthened while resisting the motion of a body part.
The astronauts who took part in extravehicular activity, as well as in the astronaut who did not, appeared to experience operationally relevant losses (>10%) of arm strength. However, the changes were not statistically significant. The effects of EVA on muscle performance require further study. Loss of muscle mass during space flight could increase the risk of injury during routine activities. According to rehabilitation standards, 40% of the astronauts were at increased risk of a back injury, and 20% were at increased risk of a leg injury. Because these standards are based on losses in a single muscle group, while space flight affects many major muscle groups, the risks may be even higher.