It is possible that a multi-year trip to Mars may never occur. "If no method is found to mitigate loss of bone density, which could be as great as 50% or more, if left untreated over a three-year period, long-duration, interplanetary missions may be impossible," plainly states the IOM summary.
The absence of gravity robs bone of a number of important forces, says Suzanne Schneider, assistant professor of human performance and development, University of New Mexico. On Earth, along with the continual force of gravity, there is a peak force that results from walking, running, and exercise, and the rate of change in those forces. The effectiveness of those forces on strengthening bone is related to the way they are applied. "If you very slowly apply the force, it's less effective than if you just suddenly jumped or got a high peak force. So it's force and the way force ...
