ACSM POSITION STAND ON OSTEOPOROSIS AND EXERCISE

Osteoporosis is a disease characterized by low bone mass and microarch itectural deterioration of bone tissue leading to enhanced bone fragil ity and a consequent increase in fracture risk. Both men and women are at risk for osteoporotic fractures. However, as osteoporosis is more common in females and more exercise-related research has been directed at reducing the risk of osteoporotic fractures in women, this Positio n Stand applies specifically to women. Factors that influence fracture risk include skeletal fragility, frequency and severity of falls, and tissue mass surrounding the skeleton. Prevention of osteoporotic frac tures, therefore, is focused on the preservation or enhancement of the material and structural properties of bone, the prevention of falls, and the overall improvement of lean tissue mass. The load-bearing capa city of bone reflects both its material properties, such as density an d modulus, and the spatial distribution of bone tissue. These features of bone strength are all developed and maintained in part by forces a pplied to bone during daily activities and exercise. Functional loadin g through physical activity exerts a positive influence on bone mass i n humans. The extent of this influence and the types of programs that induce the most effective osteogenic stimulus are still uncertain. Whi le it is well-established that a marked decrease in physical activity, as in bedrest for example, results in a profound decline in bone mass , improvements in bone mass resulting from increased physical activity are less conclusive. Results vary according to age, hormonal status, nutrition, and exercise prescription. An apparent positive effect of a ctivity on bone is more marked in cross-sectional studies than in pros pective studies. Whether this is an example of selection bias or diffe rences in the intensity and duration of the training programs is uncer tain at this time. It has long been recognized that changes in bone ma ss occur more rapidly with unloading than with increased loading. Habi tual inactivity results in a downward spiral in all physiologic functi ons. As women age, the loss of strength, flexibility, and cardiovascul ar fitness leads to a further decrease in activity. Eventually older i ndividuals may find it impossible to continue the types of activities that provide an adequate load-bearing stimulus to maintain bone mass. Fortunately, it appears that strength and overall fitness can be impro ved at any age through a carefully planned exercise program. Unless th e ability of the underlying physiologic systems essential for load-bea ring activity are restored, it may be difficult for many older women t o maintain a level of activity essential for protecting the skeleton f rom further bone loss. For the very elderly or those experiencing prob lems with balance and gait, activities that might increase the risk of falling should be avoided. There is no evidence at the present time t hat exercise alone or exercise plus added calcium intake can prevent t he rapid decrease in bone mass in the immediate postmenopausal years. Nevertheless, all healthy women should be encouraged to exercise regar dless of whether the activity has a marked osteogenic component in ord er to gain the other health benefits that accrue from regular exercise . Based on current research, it is the position of the American Colleg e of Sports Medicine that: 1. Weight-bearing physical activity is esse ntial for the normal development and maintenance of a healthy skeleton . Activities that focus on increasing muscle strength may also be bene ficial, particularly for nonweight-bearing bones. 2. Sedentary women m ay increase bone mass slightly by becoming more active but the primary benefit of the increased activity may be in avoiding the further loss of bone that occurs with inactivity. 3. Exercise cannot be recommende d as a substitute for hormone replacement therapy at the time of menop ause. 4. The optimal program for older women would include activities that improve strength, flexibility, and coordination that may indirect ly, but effectively, decrease the incidence of osteoporotic fractures by lessening the likelihood of falling.