Osteoporosis is a big issue for post-menopausal women
Load-bearing physical activity before a meal can reduce risk of osteoporosis
Osteoporosis is a serious health condition that diminishes quality of life and increases risk of fractures, especially of hip and thigh bones. Physical activity, properly applied, and nutrition can slow the rate of loss of bone strength especially for post-menopausal women. Researcher Katarina Borer proposed seven principles of bone adaptation to mechanical stress that can increase the effectiveness of exercise to maintain bone health.
Principle 1: Adaptive bone response requires dynamic and rhythmic rather than static mechanical stimulation. Principle 2: Adaptive bone response requires a supra-threshold intensity, like what an athlete might employ. The requirement for threshold stimulation means that mechanical stimuli can be either a) more frequent and of less intensity, or b) less frequent and of more intensity. Principle 3: Creation of new bone cells is proportional to strain frequency. The requirement for threshold stimulation means that mechanical stimuli can be either a) more frequent and of less intensity, or b) more frequent and of more intensity. Principle 4: Adaptive bone response improves with brief, intermittent exercise, allowing for 6-8 hours of rest between sessions. Principle 5: Adaptive bone responses require an unusual pattern of loading, perhaps running on a rocky trail. Principle 6: Adaptive bone response requires abundant nutrient energy. Principle 7: Adaptive bone response requires plenty of calcium and vitamin D3, especially before puberty and after menopause.
Exercise training can induce post-menopausal women to modestly increase bone mineral density. Improvement can arise from either joint reaction forces produced my muscle contractions and/or by ground reaction forces from load-bearing activities. However, the optimal pattern of exercise type, intensity, loading, and timing remain unclear. Researchers at the University of Michigan devised a 30-week randomized, clinical trial in which 82 post-menopausal women (average age 58 years) walked 4.8 km (2.9 miles) four days a week at one of two intensities. Low- and high-intensities corresponded to 67 or 86 percent of maximal oxygen intake, respectively. Dual-energy x-ray absorptiometry (DEXA) determined bone mineral density.
After 15 weeks, areal bone mineral density of total body, legs, and pelvis all increased in the high-intensity group but declined in the low-intensity group. At 30 weeks, only the areal bone mineral density continued to improve for the high- versus low-intensity group. In addition, the lean mass of legs increased at both 15 and 30 weeks for women in the high- compared to low-intensity group. Markers of bone formation did not differ between groups at either 15 or 30 weeks. This study found that exercise of at least 74 percent of maximal oxygen intake at a speed of at least 6.14 kph (3.7 mph) preserved bone mineral density and increased leg muscle mass in post-menopausal women.
Mechanical loading that induces bone-building may require high-magnitude strains at high rates. Conventional thinking limits such interventions for post-menopausal women with low bone mass due to possible increased of risk of fractures. Researchers in Australia found that fracture risk may be overstated. One hundred one post-menopausal women (average age 65 years) participated in a supervised, 8-week high-intensity resistance and impact physical training program with twice weekly, 30-minute sessions. All participants exhibited low bone mass with T-scores less than -1. Exercises were performed in five sets of five repetitions each at 85 percent of the one-repetition maximum. Participants in the control group performed a twice-weekly, home-based, 30-minute moderate-intensity program designed to build balance and mobility.
The high-intensity program led to significant improvements in lumber spine and proximal femur bone mineral density compared to the control group. In addition, participants in the high-intensity group showed significant improvements in six measures of physical function (leg strength, back strength, time up-and-go, stand-to-sit, functional reach, and vertical jump). Finally, none of the participants reported serious injuries, plus attrition was low. Thus, the supervised high-intensity exercise program proved both efficacious and practical for post-menopausal women with low bone mineral density.
The researchers at the University of Michigan also studied whether a meal either preceded or followed by 40 minutes of walking either downhill or uphill would promote bone mineral deposition. Participants included 15 post-menopausal women with type 2 diabetes, which predicts increased risk of fractures independent of bone mineral density. Relative to a no-exercise control group, post-meal exercise increased the ratio of a bone-building compound to a bone-resorption compound. The increase occurred due to increase in the bone-building compound (C-terminal propeptide of type 1) rather than a decrease in the bone-resorption compound C-terminal telopeptide of type 1 collagen).
Previous research showed that exercise can prevent or at least mitigate osteoporosis in post-menopausal women. A recent controlled trial provided clarity regarding the timing an intensity of exercise with respect to meals and circadian rhythms. Forty post-menopausal women were randomized one of five regimens: 1) sedentary control, 2) walking uphill for 20 minutes followed by 7 hours of rest followed by 20 minutes of walking uphill, 3) walking downhill for 20 minutes followed by 7 hours of rest followed by 20 minutes of walking downhill, 4) walking uphill for 40 minutes, and 5) walking downhill for 40 minutes. Participants ate three prescribed meals during day of the exercise training.
Levels and ratios of chemicals in the blood linked to bone formation (C-terminal propeptide of type 1 collagen, osteocalcin, and bone-specific alkaline phosphatase) and resorption (C-terminal telopeptide of type 1 collagen) provided evidence of bone formation. The 40-minute walking downhill at 6.4 kph (3.8 mph) exercise regime within an hour after a meal produced the greatest evidence of bone formation. However, 45-minute walking on level ground at 6.4 kph (3.8 mph) exercise regime within an hour after a meal would also be effective. Post-menopausal women who want to reduce their risk of osteoporosis should consider fast walking for 45 minutes following a meal to promote bone formation.
A recent systematic review and meta-analysis included 75 controlled trials that investigated the effects of various types of exercise on lumbar spine, femoral neck, and total hip bone mineral density. Analyses showed modest but significant effect sizes of exercise in spite of major differences among the included studies and evidence of significant publication bias (exclusion of studies that did not show significant effects). The exercise groups generally showed small improvement in bone mineral density, while the control groups showed small declines. This meta-analysis did not include exercise intensity or frequency due to limited numbers of studies. Perhaps a better approach would have been to pick studies with the best results and find the commonalities among them.
The following appear to reduce modestly the risk of osteoporosis, especially for post-menopausal women: Load-bearing exercises conducted at relatively high intensities shortly after eating a meal. It’s worth mentioning that these exercises will likely produce other benefits, such as improved physical strength and possibly balance.
