As a result, standing and walking, which require adequate balance, were temporarily affected. Researchers already know prolonged weightlessness results in a loss of muscle strength and decreased bone density. Currently, the only known treatment for this problem is in-flight exercise. A goal of the H-Reflex experiment is to help researchers determine if exercise could be made more effective on long space flights. The experiment measures spinal cord excitability - its ability to respond to stimuli.
Researchers believe that spinal cord excitability decreases during prolonged space flight.
If this proves true, they hypothesize that in-flight exercise would be less effective and the space crews will have to work harder and longer to achieve any benefit. If spinal cord excitability does decrease on prolonged flights, researchers may be able to reverse the effect and lower the amount of exercise now required in space and thus increase space crewmember productivity during the flight. In the experiment, a mild electrical shock will be applied to the back of the crewmember's knee. The response, called the Hoffmann reflex, is measured by recording the calf muscle contraction that results. The more twitching there is, the more spinal cord excitability there is.