1.Physical factors

Exercise during weightlessness has been incorporated into the present countermeasure programs; however, exercise alone cannot prevent bone loss. The current exercise program for the ISS is a combination of aerobic and resistive exercise for 2.5 hours, 6 days/week. Data from spaceflight revealed that bone loss occurs mainly in the femur, tibia, calcaneus, and vertebrae. Therefore, exercise should be concentrated on these bones, and impact loading should be primarily provided rather than static loading [62].
