Functional adaptation of bone to exercise and injury.

Bone adapts to altered physical stimuli, dietary changes, or injury. Dietary calcium and vitamins play important roles in maintaining skeletal health, but high-fat diets are pervasive in western cultures and may contribute to the increasing prevalence of osteoporosis and incidence of related hip fractures. Exercise helps maintain bone mass and counter osteoporosis, but exercise can also have detrimental effects-particularly for immature bone. Some negative exercise effects may also be linked to diet. For example, insufficient dietary protein during exercise can impair bone development and remodeling. Bone remodeling is a potent example of tissue repair. Chronically altered loading after a joint injury, however, can result in remodeling processes that can be detrimental to the joint. Anterior cruciate ligament injury, for example, commonly leads to osteoarthritis. Early changes in the periarticular cancellous bone may play a role in the development of knee osteoarthritis. Although these factors influence skeletal health, the mechanisms remain unclear by which bone interprets its environment and responds to mechanical stimuli or injury. To understand why different levels of exercise are beneficial or detrimental or why altered joint loading leads to changes in periarticular bone structure, underlying mechanisms must be understood by which bone interprets its mechanical environment.