ABSTRACT: Because of concerns raised by recent studies about the safety of hormone replacement therapy, attention has shifted to alternative therapies for prevention of osteoporosis. Resistance training has been shown to strengthen skeletal muscles, increase bone mineral density (BMD), and reduce fractures. Low-impact aerobic exercises, such as walking, improve cardiovascular fitness but do not create enough stress to increase BMD or muscle mass. A basic resistance training regimen consists of 5 or 6 weight-bearing exercises performed 2 or 3 times a week. Results can be seen in 4 to 6 weeks.
As the population ages, the incidence and prevalence of osteoporosis will increase. Nearly 15 million persons have osteoporosis, and another 34 million have low bone mineral density (BMD). Nearly half of persons who are older than 50 years have one of these conditions.1
Osteoporosis results in over 1.5 million fractures annually, at a cost of more than $17 billion.2 One of every 2 women and 1 of 8 men older than 50 years sustains a fracture attributable to osteoporosis.3 It is a leading cause of morbidity and disability in the elderly. A third of men who have hip fractures die within 1 year. Osteoporosis results in over 432,000 hospital admissions, 2.5 million physician visits, and 180,000 nursing home admissions annually.
Unlike many other diseases, osteoporosis is a condition that can largely be prevented or delayed. Exercise, one of the safest and most effective therapies available, is, unfortunately, one of the most overlooked. In this article, we focus on the benefits of resistance training-an activity that many experts believe should be part of a comprehensive program to prevent osteoporosis.
Osteoporosis results from an imbalance between bone formation and bone resorption. In elderly persons, loss of BMD is caused by an increase in osteoclast bone resorption activity and a decrease in osteoblast-mediated bone formation. Risk factors include advanced age, decreased gonadal function, white race, corticosteroid use, low calcium intake, and physical inactivity.
Results of the Women's Health Initiative (WHI) focused attention on hormone replacement therapy (HRT) for the prevention and treatment of osteoporosis.4 The primary outcome measure was coronary heart disease; hip fracture was a secondary outcome. The results showed a one third decrease in hip fractures and a 24% decrease in total fractures among the treatment group. However, the study was stopped early because of an increased risk of invasive breast cancer and cardiovascular disease in the treatment group. The authors concluded that HRT should not be prescribed for prevention of osteoporosis unless the fracture risk benefit was greater than the risk of cardiovascular disease or breast cancer.
Two additional trials, the Heart and Estrogen/progestin Replacement Study (HERS) and its follow-up, HERS II, found that after a mean follow-up of 4 years, there was no significant decrease in hip or total fracture rates in the HRT group.5
Following publication of the results of these studies, attention has focused on alternative therapies for osteoporosis prevention.
BENEFITS OF EXERCISE
Exercise-and specifically resistance training-has consistently been shown to reduce fractures.6-14 In addition, exercise has many other well-documented benefits, such as improving dyslipidemia, reducing the incidence of heart disease and diabetes, and ameliorating depression. There are few side effects or true contraindications. Unfortunately, few patients are counseled about the need for exercise or shown the proper techniques.
Not all exercise offers the same type of benefits. Aerobic exercise uses large muscle groups and is performed continuously at a regular pace, thus accelerating heart rate. As a result, this type of exercise generally improves cardiovascular fitness. However, aerobic exercise, particularly low-impact exercise such as swimming, does not create enough stress to increase BMD or muscle mass. Therefore, a comprehensive program should include both aerobic exercise and resistance training.
The value of resistance training. Anaerobic exercise, which consists of resistance or weight training, is an important element in a program of osteoporosis prevention.Resistance training is defined as strengthening of skeletal muscles through voluntary activation against some form of external resistance, such as body mass, free weights, or machines. Weight-bearing exercises such as resistance training increase BMD, thereby strengthening the musculoskeletal system and reducing fracture risk. Brief, high-intensity periods of loading that generate a diversity of strain patterns on the bones provide the maximal osteogenic response. They also increase blood flow to the bones.
One study compared a walking program with resistance training in menopausal women. The researchers found that the women in the walking group continued to lose BMD while the women who performed resistance training did not lose BMD.15
In addition to its effects on BMD, resistance training can increase muscle strength and other parameters. Fiatarone and colleagues16 conducted a randomized, placebo-controlled trial comparing high-intensity progressive resistance training, nutritional supplementation, both interventions, and neither in 100 frail nursing home residents over a 10-week period. Training sessions were held 3 days per week and lasted 45 minutes. At the end of the study period, patients in the resistance training program showed a 113% increase in muscle strength compared with 3% in the non-exercising group, an 11% increase in gait velocity in exercisers compared with 1% in the non-exercising group, and a 28% increase in stair-climbing power compared with 3% in the non-exercising group. Of note, nutritional supplementation had no significant impact on any primary outcome measure.
Evidence for the effects of resistance training on osteoporosis prevention continues to mount. The recent FICSIT trials (Frailty and Injuries: Cooperative Studies of Intervention Techniques), a multicenter study funded by the NIH, also determined that resistance training (among other modalities) reduces falls.17 This is important because it may ultimately result in a reduction in fall-related fractures.
Resistance to resistance training. The reasons for lack of widespread participation in resistance training include lack of knowledge about technique and fear of injury. In addition, many women believe that if they start lifting weights, they will become muscle-bound. However, this effect is highly unlikely for women in a typical resistance training program. In fact, resistance training is generally safe, simple, and time-efficient. Introduce your patients to the benefits of resistance training and allay fears that may be misguided. Numerous Web sites and resources are available to help patients learn proper form and technique (Box I).
A sampling of exercises designed to help prevent osteoporosis is shown in Box II on page 1005. They can be performed at home by persons of any age and at any fitness level. n
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