When astronauts are exposed to microgravity, as onboard the International Space Station (ISS), they experience significant physiological deconditioning, a phenomenon referred to as space deconditioning (SD). In order to attenuate the effects of SD, astronauts have to exercise on a daily basis for approximately two and a half hours, using a treadmill, a cycle ergometer and a resistive exercise machine. This daily exercise has been shown to be largely effective in preserving the integrity of bones, muscles and the cardiovascular system, so that astronauts return to Earth in a very reasonable physical shape.
It was recently announced that after the era of the ISS, ESA will aim to leave lower earth orbit to pursue human space flight explorations in deeper space. It is a very likely scenario that humans will, as a first step, return to the Moon environment to build a lunar habitat that could serve as both a space research laboratory and as an intermediate stepping stone for further space exploration.
Given the nature of the Moon and considering that its gravity is approximately 17% of that of Earth, long term missions to the lunar surface will constitute new challenges to human physiology. Physical exercise will most likely be a first choice intervention to counteract physiological deconditioning expected to occur on the lunar surface.