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High exercise frequency ‘essential’ for affecting BMD in postmenopausal women
Postmenopausal women with osteopenia should exercise for at least two sessions per week in structured, 65-minute group sessions or 25-minute home training sessions to preserve bone mineral density at the lumbar spine and hip, according to recent study findings.
“While higher intensity may partially compensate for borderline [exercise frequency], maintaining adequate exercise participation of at least two sessions/week is essential for relatively affecting BMD,” Wolfgang Kemmler, PhD, of the Institute of Medical Physics at University of Erlangen in Germany, and colleagues wrote. “Although we focus on early-postmenopausal osteopenic females, we speculate that the ‘critical exercise frequency’ for favorably addressing BMD will not be significantly different for other adult cohorts.”
Kemmler and colleagues analyzed data from 55 healthy postmenopausal women with osteopenia participating in the Erlangen Fitness and Osteoporosis Prevention study, a controlled exercise trial focusing on clinical fractures and BMD, between 1998 and 2014. Women were free to join the exercise group, which conducted an intense, multipurpose exercise program aimed at bone health, or a nontraining control group (n = 43).
The exercise protocol included four weekly exercise sessions, structured as two consistently supervised group sessions and two home training sessions for 49 to 50 weeks per year for 16 years. Group sessions (65 minutes) included aerobic dance, low- and high-impact exercises and periodic weight training. Home training sessions (20-25 minutes) consisted of a warm-up sequence, resistance exercise, and stretching and flexibility exercises.
Researchers used the control group data in this study to determine the cutoff value for exercise effectiveness. All participants completed baseline and follow-up questionnaires and structured interviews to detect changes in confounding parameters over time; all were supplied with calcium and vitamin D supplements based on dietary records kept by the study participants.
To determine the isolated effect of exercise frequency during the 16-year study on BMD at the lumbar spine and total hip, researchers used linear mixed-effect regression analysis with BMD as the dependent variable with data from years 4, 8, 12 and 16.
After 16 years, average exercise frequency ranged between 1.02 and 2.96 sessions weekly (mean, 2.28 sessions weekly). Researchers found that exercise frequency had an independent effect on lumbar spine (P < .001) and total hip BMD (P = .005). In the exercise group, lumber spine BMD decreased by 1.5% after 16 years (95% CI, –0.1 to –2.8) vs. an increase of 5.8% in controls (95% CI, –3.3 to –7.2); total hip BMD decreased by 5.7% (95% CI, 4.8-6.7) vs. 9.7% for controls (95% CI, 8.1-11.2).
In bootstrap analysis, the minimum effective dose was found to be about two sessions weekly during 16 years. The cutoff for lumbar spine BMD was 2.11 (95% CI, 2.06-2.12); the cutoff for total hip BMD was 2.22 (95% CI, 2-2.78).
“Here, our data were very disillusioning, since this study clearly demonstrates the close positive association between [exercise frequency] and bone maintenance in the realistic range of one to three sessions per week, and confirmed our prior data that the ‘minimum effective dose’ for relevantly impacting BMD averaged at least around two sessions per week for [lumbar spine] and total hip,” the researchers wrote. “Although this result might not be generalizable across all exercise types and protocols, it does at least suggest that even when applying high-impact/high-intensity protocols, [exercise frequency] and its maintenance play a key role in bone adaptation.” – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.