An article was recently published bringing to light the long-term back problems of astronauts that have spent extended time periods in space. Due to the reduction in gravity, astronauts experience less force on their bodies, and are actually known to "grow" two inches while in space. While this may seem like a good thing to reduce the forces on our bodies, this loss of gravity can length the torso, weaken the spine, and lead to a host of physiological problems. The article brings up possible future (nearly month long) missions to Mars that could come with the risk of more back pain and muscular atrophy.
Mars has a gravitational pull 38% of Earth's surface gravity, meaning that it would be 3.7 m/s^2. A 70 kg person on Earth would feel a force due to gravity of 686 N while the same person would feel a force due to gravity of only 259 N on Mars.
(70 kg)(9.8 m/s^2) = 686 N
(70 kg)(3.7 m/s^2) = 259 N
The article went on to talk about the benefits of astronauts doing strength exercises and yoga to alleviate the negative effects of loss of gravity. However, yoga depends on using the force of gravity to stretch muscles. In addition, many strength training exercises only work because the force of tension of the muscles are opposing the force of gravity (concentric contractions) or because gravity is greater than the opposing muscle contraction (eccentric contractions). If the force due to gravity is significantly lower in space or on another planet, then these exercises will be less effective. If the Fg is lower, then the Ft of the muscles will be lower to overcome or oppose it. Better exercises need to be developed and implemented in order to avoid these long term problems in the future.
Read the article here: http://www.cnn.com/2016/10/26/health/astronaut-back-pain-spine-health-space/index.html