How it accomplishes this feat is still being examined. Exercise may be directly affecting bone by stimulating metabolic hormones that influence such growth. There's considerable evidence that exercise also indirectly affects bone by applying force on the muscles connected to bone. The more a muscle is moved, the more electromagnetic resistance develops between muscle and bone, and the more bone stays primed in response to that stress. When bone isn't stressed by muscle, it can break down rapidly.
Any physical activity is better than none at all.
When bone density increases, to whatever degree, the greatest buildup occurs in those locations most influenced by exercise. Another observation was that when exercise contributes to bone buildup, the body appears to reach a plateau after which further exercise does not increase bone density. Unfortunately, few studies to date tell us exactly what type of exercise best benefits bone. With weight-bearing exercises, your body weight serves as the load to strengthen muscles and bone, in comparison to resistance training, which makes use of an external load. Pedaling a stationary bike is considered a light weight-bearing exercise.