Astronaut muscles waste away on long space flights reducing their capacity for physical work by more than 40 percent, according to new research. This is the equivalent of a 30- to 50-year-old crew member's muscles deteriorating to that of an 80-year-old. The destructive effects of extended weightlessness to skeletal muscle -- despite in-flight exercise -- pose a significant safety risk for future manned missions to Mars and elsewhere in the universe.