Changes in pressure and force that occur during daily activities and exercise cause bones to develop mass and strength. When you move your body against the force of gravity and do exercises that strengthen muscles, you are producing forces that push and pull on your bones. Bones respond to this kind of movement and become stronger. You lose bone mass when you do not put weight on your bones. For instance, anyone who cannot get out of bed or does not walk loses bone mass and has an increased risk of fracture.
Astronauts do special exercises while they are in space to keep from losing bone mass.
This is important because they are weightless in space and cannot exercise against gravity. Some exercises or activities that use gravity and your muscles to strengthen your bones are listed below. If you do them regularly and quickly, some are also good for your heart. Exercise helps you move more easily and keep your balance, which helps you avoid falls. Experts do not know exactly how long you must exercise to prevent loss of bone mass.