Osteoporosis is defined as a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue with a consequent increase in generalized skeletal fragility, such that fractures occur with minimal trauma (13). Osteoporosis involves reductions in both bone mineral density (BMD) and bone quality. Osteopenia is defined as a bone density between 1 and 2.5 standard deviation units below average and places the individual at greater risk for osteoporosis (12). The risk of fracture increases with age for the osteopenia patient.
Osteoporosis has a debilitating effect on independence and quality of life. Risk factors for osteoporosis are family history, female gender, estrogen deficiency, low weight, dietary factors, prolonged use of corticosteroids, smoking, and physical inactivity (3). Exercise therapy, particularly resistance-based and weight-bearing activity may increase bone material and modify several risk factors for osteoporotic fracture, including muscle strength, bone-mineral density, and dynamic balance (12). Bone mass attained early in life is perhaps the most important determinant of lifelong skeletal health (9). Nutrition, exercise, and body composition all play a key role in bone density. Exercise can positively affect peak bone mass in children and adolescents, maintain or even modestly increase bone density in adulthood, and assist in minimizing age-related bone loss in older adults. Therefore, exercise programming should be presented to optimize bone health and to safely prescribe exercise for individuals with existing low BMD.
Osteoporosis and Exercise
Bone is a spongy protein matrix in which crystals of calcium and phosphorus salts are embedded (11). In many bones, there are two distinct regions: an outer, dense shell of compact bone (cortical) and an inner, open, sponge-like region of cancellous bone (trabecular). Once produced, bone does not remain as a fixed structure. From birth until death, bone tissue is continually being formed, broken down, and re-formed in a process called remodeling. The cells that break down bone are called osteoclasts, and those that build bone are called osteoblasts.
It is well known that humans lose bone mass rapidly when gravitational or muscle forces on the legs are decreased or become absent, as in weightlessness, bed rest, or spinal cord injury (17). Healthy individuals who undergo complete bed rest for 4-36 weeks can lose an average of 1% bone mineral content per week, while astronauts in a gravity-free environment can lose bone mass at a monthly rate as high as 4% for trabecular bone and 1% for cortical bone (2). The bone adapts to imposed stress or lack of stress by forming or losing mass (4). The bone becomes bigger and denser when stress is applied in excess of normal levels because of stimulation or remodeling. The bone will continue to grow and adapt until it is restructured to handle the new imposed stress.
There is substantial data showing that athletes have a greater bone density than sedentary controls (5, 6, 7, 15). Weight-bearing activities such as walking, running, and racket sports are more effective in maintaining density of leg and spinal bones than non-weight-bearing activities such as bicycling and swimming. The athletes with the greatest bone mineral masses are weight lifters, followed by athletes throwing the shotput and discus, then runners, soccer players, and finally swimmers.
A significant relationship exists between lifetime physical activity, bone mineral mass, and lowered risk of hip fracture in men and postmenopausal women (5, 6). Children who engage in sports that produce significant impact loading on their skeletons (e’g running, gymnastics, and dance) have greater femoral neck bone density than children in sports producing low-impact loads to the bones (eg swimming) (7, 15). This is considered important because a higher peak bone mass may be experienced in these individuals if exercise is maintained, decreasing the risk of osteoporosis later in life.
Several studies have shown the value of intensive resistance and weight-bearing training in protecting the skeletons of postmenopausal women (10, 14, 16). In a 1-year study of 39 postmenopausal women, subjects engaged in intensive weight training for 45 minutes, two times a week. The weight training women improved their strength and muscle mass, and also their bone mineral density when compared to the control subjects (14). In another 1-year study of postmenopausal women (32 women, 60-72 years of age), subjects walked and jogged and climbed stairs vigorously for 50 minutes a session, three to four times a week. Exercise and estrogen therapy together had the greatest effect on lumbar bone density, with about one third of the improvement due to exercise (10). These results suggest that the efficacy of estrogen therapy is enhanced by combining it with weight-bearing exercise. Other research has indicated that the regimen of intensive exercise must continue indefinitely because just as quickly as the bone mineral density is gained it can be lost through detraining (16).
A potential benefit of regular exercise by the elderly is a decrease in the risk of falling. Falls and the resulting injuries are among the most serious and common medical problems suffered by the elderly. Each year, about 3 in 10 elderly individuals sustain a fall, with somewhat less than 5% of falls resulting in bone fractures.
In its position statement on osteoporosis and exercise, the American College of Sports Medicine has urged that “ the optimal program for older women would include activities that improve strength, flexibility, and coordination that may indirectly, but effectively, decrease the incidence of osteoporotic fractures by lessening the likelihood of falling” (1). Although more research is needed, some studies suggest that exercise directed towards balance and lower extremity strength training may reduce the risk of falling (8). There is good evidence that physical activity is linked to a 20-40% reduced risk of hip fracture (8). In other words, regular weight-bearing and resistance exercise has a twofold benefit for the elderly-an improvement in bone mineral density and a reduced likelihood of falling leading to fractures.
If you have or are at risk of developing Osteoporosis, learn about how Osteoporosis is a chronic disease which is eligible to receive a Medicare Rebate when seeing an Accredited Exercise Physiologist:
Did you know you could get up to 50% off with a Medicare Rebate?
Learn how an Accredited Exercise Physiologist can help you to begin and maintain exercise in your life, so you can enjoy the health benefits of Exercise for Osteoporosis:
What Does an Exercise Physiologist Do?