Bemben, A., Fetters, Bemben G., Nabavi, and Koh (2000) compared the muscular strength and BMD effects as measured by dual energy X-ray absorptiometry (DEXA) of a high-load and a low-load weight training protocol on a small sample (N = 25) of estrogen-deficient, healthy women (41 to 60 years of age) who were randomized between the high-load (80% 1-RM), low-load (40% 1-RM), and a sedentary control group. The study found that both experimental groups had shown similar overall increases in muscular strength but no significant increases in BMD of the femur, hip or lumbar spine after six months when compared to the control group. Interestingly, the high-load group had shown a noticeable reduction in overall BMD while the low-load group indicated no significant change in overall BMD. The control group had shown a decrease in BMD. The authors concluded that low-intensity strength training may be just as effective as high-intensity training in preventing bone loss and increasing strength.
Low-intensity strength training is the recommended exercise prescription for older populations. Older people tend to adapt and progress more readily when prescribed a low-load, high-rep protocol for exercise programming. This type of program is also recommended for people with osteopenia and/or osteoporosis whose weakened bones may not be able to withstand the stress of high-intensity training. Some limitations of the Bemben et al. study include small sample size and lack of blinding between the groups. The primary criticism though is the lack of adequate testing duration (six months) to provide conclusive data in determining the correlation between increasing muscular strength and BMD. It is commonly known that the bone remodeling cycle of resorption and formation is known to take four to six months to occur. Thus, the duration of this study should probably have been extended to at least nine months to confirm the results of the data.
Kerr, Ackland, Maslen, Morton, and Prince (2001) investigated the effect of weight training exercise on BMD using DEXA in post-menopausal women (N=126). The two-year study compared the BMD of three randomized groups: strength group (N=24); fitness group (N=30); and a sedentary control group (N=36). The strength group performed exercises with increased loading while the fitness group performed the same exercises in circuit fashion with minimal resistance increases. The findings indicated that BMD increased markedly only at the hip (P < 0.05) after progressive resistance exercise in the strength group. The authors concluded that progressive loading on the bones from strength training is required to increase BMD.
Shackelford et al. (2004) studied how an intense resistance exercise regimen provided the stimulus needed to reduce BMD loss, measured using DEXA, caused by disuse. The sample size of the exercise group (23-44 years of age) was small (N=9) and a control non-exercise group (22-56 years of age) was utilized to compare the noticeable effects of resistance exercise during bed rest. Assignments in either group were not chosen randomly, possibly skewing the results. The testing duration was reduced (17 weeks), possibly limiting result confirmation. Utilizing a specially-designed Horizontal Exercise Machine to stimulate BMD, it was found that the exercise group exhibited a substantial increase in lumbar spine BMD (~ +3.4%) compared to the control group (~ -1.3%) with statistical significance (P < 0.05) in both parameters. In addition, there was less reduction in BMD in the femur, hip and pelvis of the exercise group (~ 0.1%) but decreased somewhat in the control group (~ -0.7%) with P < 0.05 for both parameters. In addition, total body mass increased more in the strength group (~ +2.3%) than in the control group (~ +1.0%). Also, lean body mass of the exercise group increased (~ +3.9%) while that of the control group decreased (~ -4.0%) with P < 0.05 for both parameters. Finally, overall strength levels increased in the exercise group but decreased in the control group. The authors concluded that resistance exercise has a positive effect in reducing bone loss while increasing muscle mass and strength levels.
Resistance training and weight-bearing exercise such as walking is highly recommended as the first step in the prevention of osteoporosis. It is known that bone and muscle mass will inevitably decrease during the aging process when accompanied by a reduction in weight-bearing exercise. Thus, resistance training may reduce the slow decline on bone mass caused by BMD loss. This form of anaerobic exercise has the potential to not only reduce bone loss, but also to improve posture, muscle strength, coordination, and balance as well. Better balance reduces the likelihood of falls and the risk of fractures. Regular physical exercise helps to stimulate bone growth, preserve bone mass, and even increase BMD. Examples of this type of exercise include weight-lifting, hiking, stair-climbing, step aerobics, dancing, tai chi, and other activities which require the muscles to work against the force of gravity. Because osteoporosis occurs more frequently in post-menopausal women (low estrogen levels), more research is available which studies the effects of strength training in this group.
In conclusion, the investigated peer-reviewed research has provided clinical significance that resistance training, whether of low-intensity or high-intensity, may prevent bone loss as well as increase strength and muscle mass. Despite the relatively small sample sizes in each of the research studies, a trend linking resistance exercise and BMD maintenance was ascertained. Kerr et al. provided data results of BMD from a relatively longer-duration period (2 years) utilizing a larger sample size. Thus, this particular study has provided greater credibility to the findings (the results may be generalized to more general populations) in showing that progressive resistance exercise may maintain or even increase BMD. The overwhelming evidence from all of the aforementioned studies has indicated that resistance exercise will increase muscle mass, increase strength levels, and reduce bone loss caused by osteoporosis.
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."