Weight-bearing exercise is recommended to maintain bone strength, and is especially important as we age. This includes any sustained activity that you do against the force of gravity, such as jumping or running. When bone is strained, as when doing weight-bearing activity, the body triggers the release of cells that help build up the bone in that area.
As we age and no longer build bone automatically, exercise becomes even more important.
The best bone-strengthening exercises are: running, jumping rope, aerobics, dance, basketball, volleyball, tennis, skiing, stair climbing, hiking and weight lifting.
Exercises such as walking, low-impact aerobics, using workout machines, swimming and cycling, while good for cardiovascular health, provide less bone-building benefit. However, combining at least three sessions of weight-bearing exercise into your daily exercise program packs a double punch. Try walking and then lifting weights, for example, or swimming and dancing. Whatever you do, research suggests that short bouts of weight-bearing exercise (15-20 minutes) are more beneficial than longer sessions.
— Source: University of California Berkeley Wellness Letter