Exercises such as running, walking, hiking, stair climbing, weight training, tennis and dancing force you to work against gravity.
Active bones are denser bones.
The reason weight-bearing exercise better prevents bone loss is that it helps bones absorb calcium and build mass. The best way to prevent bone loss is to begin weight-bearing exercising at a young age, says John Anderson, professor of nutrition at University of North Carolina School of Medicine. In those years girls build most of their bone mass. For boys, the most important age is between 10 and 20. The combination of exercise and a steady intake of calcium is the best way to prevent bone loss.