Elsevier

Joint Bone Spine

Volume 76, Issue 3, May 2009, Pages 273-280
Joint Bone Spine

Original article
Effect of resistance exercise on bone mineral density in premenopausal women

https://doi.org/10.1016/j.jbspin.2008.07.016Get rights and content

Abstract

Objective

To assess the effect of 9 months of strength training on total body and regional bone mineral density (BMD, g/cm2) in 58 premenopausal women aged 30–50 years.

Methods

Participants were randomized to either twice weekly supervised strength training for 15 weeks followed by 24 weeks of unsupervised training (treatment group) or control group. Height, weight, maximal muscular strength, nutrient intake and physical activity were assessed. Total body dual energy X-ray absorptiometry (DXA, Lunar Prodigy) scans were taken and analyzed for body composition (lean and fat mass), and BMD for total body and its sub-regions (spine, hip, arms and legs). All measurements were performed at baseline, 15 and 39 weeks. Analysis of covariance was used to assess group differences in BMD change adjusted for baseline BMD, weight, energy and calcium intake.

Results

At baseline, the two groups had similar BMD and body size characteristics ( P < 0.05 for all), except that the treatment group had lower body weight (−7.1 kg), and higher energy (+259 kJ/d) and calcium (+232 mg/d) intake at baseline. Adjusted % change in BMD over 15 weeks (0.5% vs. 0.4%) or 39 weeks (0.9% vs. 1.2%) did not differ significantly between the exercise and control groups, respectively. The exercise group increased BMD at the spine and legs (1–2.2%), while there was no change in the controls, but differences between groups were not significant.

Conclusion

Strength training over 9 months did not lead to significantly greater change in total body or regional BMD in premenopausal women.

Introduction

Peak bone mass in women is attained between late adolescence and the third decade [1], [2], [3], [4], and thought to be a predictor of osteoporosis risk in postmenopausal years [5]. Besides genetic and hormonal factors, modifiable factors including calcium intake and physical activity make a significant contribution to peak bone mass and are determinants of risk for osteoporosis [6], [7], [8], [9], [10]. Cross-sectional studies in premenopausal women consistently showed higher bone mineral density (BMD, g/cm2) in women who perform weight-bearing or strength-training exercise compared to normally active controls [11], [12], [13]. Results of randomized controlled trials of strength training in premenopausal women (Table 1) are conflicting [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]. Studies show increased BMD or reduced bone loss [17], [20], [21], [24], no effect [14], [15], [16], [18], [19], [23], [25] or, in one case, increased bone loss [22] with strength training. Despite these conflicting results, strength training is often promoted for increasing BMD in premenopausal women [6]. We performed a randomized controlled trial of strength training in premenopausal women to explore change in body composition (lean and fat mass) over 9 months [26]. Total body DXA scans were used to assess change in lean and fat mass as previously published [26]. As the effects of strength training on BMD in women are conflicting, we used bone data from the study to examine changes in total body and regional BMD in premenopausal women. Total body BMD is correlated with regional BMD in studies of total body DXA scans [27], [28]. Thus, we performed a secondary analysis of these data to examine the effect of 9 months of strength training on BMD in premenopausal women.

Section snippets

Subjects

During December 1999 and January 2000, 58 premenopausal women aged 30–50 years were recruited from female faculty, staff, or students at the University of Minnesota. Women were recruited for an obesity prevention intervention study, which has been previously described in detail [26] and the current study assessed the effect of exercise on bone mineral density as secondary data analysis. Women were screened for the following inclusion criteria: (1) self-reported BMI between 20 and 35 kg/m2; (2)

Results

Descriptive characteristics for the 54 women who completed the study are reported (Table 2). The mean age was 41 years and most of the women had completed college. Average BMI was 25 or greater (kg/m2) in both groups. Of the 54 participants, two were African-American (one in each group), three were Asian (two intervention and one control), and 49 were Caucasian (10% minority participation). The treatment group weighed less than the control group at baseline (P = 0.04), but the groups were well

Discussion

Previous studies have shown inconsistent effects of resistance training on bone mineral density (BMD, g/cm2) in premenopausal women [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]. Our study added to previous work by exploring the effects of a strength-training only program on BMD in premenopausal women with a broad range of BMI (19–36 kg/m2) and body fat percentage (23–54%) in a randomized controlled trial. Our results showed no significant treatment effect of strength

Conflict of interest:

None of the authors has any conflicts of interest to declare.

Acknowledgement

We thank the subjects for their time and participation in the study.

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