exercise
bones are subject to two main mechanical stresses the weight that bears down on them as a result of the downward pull of gravity and the force of tension exerted by muscles as they move bones. these stresses increase during weight-bearing exercises such as walking, running, dancing, or tennis. Performed several times weekly, such exercises stimulate bone cells to reshape bones and a healthy diet pay dividends. After the age of 40, bone strength and mass decrease, but if they were enervated by regular exercise in older people can revers decreases in bone strength and mass, reducing the risk of osteoporosis