Mechanical loading, muscular activity and gravity all stimulate the bone cells to differentiate and grow. Exercise therefore initiates the bone-remodeling cycle. Bone mineral maintenance and growth depends on the type and frequency of exercise and also on gravity.
Exercise is directly associated with the laying down of matrix on the remodeling surface of bone. The need for calcium to meet the increased demands during bone remodeling is a critical factor in maximizing exercise-induced bone formation. A need for extra calcium in exercising women has been supported by a study that showed improved bone mineral accretion in women with higher calcium intake but constant equal energy expenditure.
The positive effect of exercise on bone mass may be related to an increase in muscle mass. A relationship has been demonstrated between physical activity, psoas muscle mass and lumbar vertebrae ash weight in premenopausal women and spine bone mineral content and back extensor muscle strength in postmenopausal women. Increased muscle strength, coordination and flexibility are particularly important for older women as they can prevent falls.
There is increasing evidence that site-specific exercise is the most effective eg weight- lifting is better for spinal bone mass than jogging, although jogging is more likely to be beneficial for hip bone mass. A combination of aerobic exercise and weight training is better than either one of these alone but the best exercise regimes are those tailored to the individual.
The beneficial effect of exercise on bone formation is rapidly lost if the intensity and frequency of exercise diminishes.