Effects of Altered Gravity on Spinal Cord

Prolonged weightlessness results in a weakening of the heart, a loss of skeletal muscle strength and volume, and decreased bone density. At this time, the only effective treatment for these problems is in-flight exercise. The basic unit of exercise is a single twitch contraction of one Òmotor unitÓ. If spinal cord excitability (SCE) is reduced during space flight, this would hinder motor unit recruitment. As a result, more effort would be required to produce the same level of exercise, or if the same apparent effort were maintained, the actual level of exercise would decrease. If present after landing, it would be more difficult to stand and walk.