Physical Activity for the Prevention and Treatment of Osteoporosis
Physical activity/exercise can provide an important tool for both the prevention and treatment of osteoporosis. Physical stress transmits load to the bone and can improve or maintain its structural competence and strength. Participation in weight-bearing activities during adolescence is an effective method to achieve an ample peak bone mass and to reduce the risk for the later development of osteoporosis. Postmenopause, the ideal exercise to stimulate bone mineral density would involve progressive, resistive-type training involving overloading of some nature.
Key words: functional loading, weight-bearing activities, resistance training, peak bone mass, bone mineral density.
Introduction
Osteoporosis--derived from the Greek words osteon, meaning bone, and poros, meaning small hole--is a disease characterized by low bone mass and microarchitectural deterioration of bone tissue leading to enhanced bone fragility and a consequent increase in fracture risk. Osteoporosis is more common among women over the age of 50 as a result of hypoestrogenemia, but it also affects men and can occur in individuals of any age. In addition, many chronic illnesses (e.g., asthma, inflammatory myopathies, and duchenne muscular dystrophy) involve treatment with corticosteroids, which are also known to cause elevated bone resorption and reduced bone formation, resulting in lower bone mass. The social and medical consequences related to osteoporosis include an increased risk of fracture and a reduced quality of life. Individuals with osteoporosis are likely to experience fractures with forces no greater than those applied by routine daily activity. It is estimated that there has been a four-fold increase in hip fractures worldwide since 1990.1 Osteoporosis can also result in disfigurement, lowered self-esteem, reduction or loss of mobility, and decreased independence.
As there is no cure for osteoporosis, physical activity/exercise has been suggested as a particularly effective strategy in averting the inevitable repercussions of this disease. Regular physical activity has been shown to improve or maintain the structural competence of bone. It is well established that physical activity transmits load to the bone via two mechanisms--direct impact from weight-bearing exercise and the pull that is produced by the muscle contraction. These forces lead to alterations in bone shape and, to a large degree, determine bone strength.2
Physical Activity and Osteoporosis Prevention
Childhood through to late adolescence is a significant period in bone formation, with about 50% of the peak bone mass (PBM) being acquired during this period. Peak bone mass is defined as the amount of bony tissue present at the end of skeletal maturation. Because a low peak bone mass is a significant risk factor for osteoporosis and associated fractures,3 the achievement of an ample peak bone mass during childhood and adolescence is an effective method to reduce the risk for the later development of osteoporosis. Debate continues as to the age at which peak bone mass is attained, with estimates ranging widely in cross-sectional data from late adolescence4 to the third5 and into the fourth6 decades of life. Some studies show that significant loss of trabecular bone may also occur immediately after the acquisition of PBM, even before menopause, at some sites (e.g., proximal femur).6,7 Given that the incidence of fracture in North America is about twice as great for women as it is for men, women must use all available means to achieve the highest possible peak bone mass. Since, for most sites of the skeleton, peak bone mass is established by late adolescence,7 this period of life provides the singular best opportunity to employ strategies aimed at optimizing and maintaining premenopausal