Systematically applying mechanical stress to your bones increases the strength of them. On a cellular level, your bone tissue adapts to the mechanical stresses you place on them by increasing the mineral salt deposits in them and through producing collagen fibers. Removing mechanical stress weakens bony tissue though the exact opposite processes.

A good example of a medical condition that is caused by force placed on bone is heel spurs. A heel spur is a bony protrusion on the underside of the heel bone. They are sometimes asymptomatic, and sometimes they cause pain. Heel spurs are often caused by strains and injuries in the muscles and ligaments on the bottom of the foot, which result in the significant pulling on the bony attachment to the heel hone. The bones reaction to the force of pull is to build more bone. You can see another great example of this by simply looking at the knees of professional basketball players. The repeated force of extreme jumping and running causes the bony attachments of muscles at and below the knees, to grow much bigger in professional basketball players on average than in the general population.

This is one reason why weight-bearing exercises are important for your general well being, especially as we age. If you never lift a weight of any said amount, your bones will never be able to lift that weight. If you attempt to lift more weight than your bones have adapted to be capable carrying, it will result in injury. By doing generalized weight bearing exercises as early in your life as possible in order to build your bones up and strengthen them, you’re giving yourself a good, solid foundation for aging with good bone mass and over all health.