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Taking Muscle Training to the Moon

Posted on: 11/30/1999
Ever wonder how astronauts keep their muscles strong during long flights into space? It's a question scientists have been grappling with. Aerobic exercise keeps astronauts fit, but it doesn't help them maintain muscle size and strength in the absence of gravity. Over time, the effects of this muscle "unloading" are similar to what happens after long periods of bed rest. The muscles shrink and become weak. Scientists want to know whether resistance training might help and, if so, how much astronauts need to do to maintain their muscles in space.

Thirty-two young, healthy men were divided into two groups. Half of them had one of their legs suspended in a harness for 21 days. This was to mimic the unloading or weightlessness that happens in space. The other subjects were allowed to walk around as usual.

Half of the subjects in each group did a muscle training program every three days (six sessions total). The other subjects did no special training. The muscle training program included knee extension exercises, in which the leg was bent and straightened, and exercises pointing the toes toward the sole of the foot. The training program took about 20 minutes and worked the thigh and calf muscles to exhaustion.

Did muscle training make a difference? Results showed that, while the training program didn't help subjects build muscle, it did keep them from losing muscle during 21 days of muscle unloading. It also helped them maintain healthy nerve and muscle function.

Subjects who didn't do the training program during muscle unloading lost seven percent of leg muscle. Their strength with muscle tightening (flexing the muscle without moving the leg) went down 17 percent. The strength of their active contractions (flexing the muscle while moving the leg) also went down quite a bit, especially at slower speeds. In contrast, muscle size and strength either stayed the same or improved slightly for those in training.

A program of muscle contractions done every third day prevented loss of muscle size and strength during muscle unloading. The program involved fewer contractions over a longer period of time than those used in previous studies. However, this program was still effective in maintaining muscle. More studies are needed to determine the least amount of muscle training astronauts can do during space travel and still stay strong.

References:
Kimberley Schulze, Philip Gallagher, and Scott Trappe. Resistance Training Preserves Skeletal Muscle Function During Unloading in Humans. In Medicine & Science in Sports & Exercise. February 2002. Vol. 34. No. 2. Pp. 303-313.

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