Astronauts who spend months in space become as physically weak as 80-year-olds, a study has found.
Researchers in the US made the discovery after testing muscle tissue taken from crew members on the International Space Station (ISS).
The calf biopsy samples revealed that after six months in orbit the physical work capacity of astronauts fell by 40 per cent. This was equivalent to the muscles of an astronaut aged 30 to 50 wasting away to the level of an average 80-year-old.
The deterioration occurred despite crew members taking regular exercise on the space station.
Scientists fear the effects of extended weightlessness on skeletal muscle will pose a significant safety risk for future manned Mars missions.