THE relationship between bone density and physical activity in space may someday serve as a way to assess a person's risk of osteoporosis.
Loading is important in maintaining muscle and bone strength in the lower limbs.
We are investigating new ways to counteract these changes with devices capable of imposing Earth-equivalent levels of force on the body in space. The device is a force sensor, resembling a shoe insole, connected by a cable to a small computer carried in a fanny pack, which is capable of storing about two weeks of activity data. The computer samples the applied force 100 times per second. It stores only the significant maximum and minimum forces occurring during each loading or gait cycle, as well as the peak loading and unloading rate and the time at which each event occurred. Because our muscles generate their own forces, we are limited by how strong our muscles are.