The problem of partial gravity on the Moon and Mars

Astronauts who spend many weeks or months in space in zero g suffer serious health problems including muscle atrophy, cardiovascular deconditioning, bone calcium loss, impaired vision, and immune system change. The debilitating effects of weightlessness were first demonstrated on the early Skylab, Salyut, and Mir missions, but it was too optimistically hoped that in-flight exercise and resistance training could prevent these problems. Similar problems are anticipated in the partial gravity of the Moon and Mars. Partial gravity exposure below 0.4 g seems too low to maintain musculoskeletal and cardiopulmonary conditioning in the long term. Some studies show a strong correlation between heart rate, oxygen consumption, net metabolic rate and simulated gravity from 0 to 1 g. Exposure to Moon and Mars gravities probably will cause less severe physiological deconditioning than experienced in 0 g, but the benefit of partial gravity seems likely to be roughly proportional to the 1/6 or 1/3 gravity experienced. As in 0 g, exercise countermeasures seem necessary but insufficient to preserve all physiological systems to a 1 g standard.