Elsevier

Bone

Volume 30, Issue 6, June 2002, Pages 836-841
Bone

Original article
Stronger back muscles reduce the incidence of vertebral fractures: a prospective 10 year follow-up of postmenopausal women

https://doi.org/10.1016/S8756-3282(02)00739-1Get rights and content

Abstract

The long-term protective effect of stronger back muscles on the spine was determined in 50 healthy white postmenopausal women, aged 58–75 years, 8 years after they had completed a 2 year randomized, controlled trial. Twenty-seven subjects had performed progressive, resistive back-strengthening exercises for 2 years and 23 had served as controls. Bone mineral density, spine radiographs, back extensor strength, biochemical marker values, and level of physical activity were obtained for all subjects at baseline, 2 years, and 10 years. Mean back extensor strength (BES) in the back-exercise (BE) group was 39.4 kg at baseline, 66.8 kg at 2 years (after 2 years of prescribed exercises), and 32.9 kg at 10 years (8 years after cessation of the prescribed exercises). Mean BES in the control (C) group was 36.9 kg at baseline, 49.0 kg at 2 years, and 26.9 kg at 10 years. The difference between the two groups was still statistically significant at 10 year follow-up (p = 0.001). The difference in bone mineral density, which was not significant between the two groups at baseline and 2 year follow-up, was significant at 10 year follow-up (p = 0.0004). The incidence of vertebral compression fracture was 14 fractures in 322 vertebral bodies examined (4.3%) in the C group and 6 fractures in 378 vertebral bodies examined (1.6%) in the BE group (chi-square test, p = 0.0290). The relative risk for compression fracture was 2.7 times greater in the C group than in the BE group. To our knowledge, this is the first study reported in the literature demonstrating the long-term effect of strong back muscles on the reduction of vertebral fractures in estrogen-deficient women.

Introduction

Reduction in the biomechanical competence of the axial skeleton can result from the parallel decline in bone and muscle mass with aging. Inactivity also may contribute to this decline.18 Participation in a strength training program can decrease the risk of falls and fractures of the lower extremities.21

One study of the effect of strengthening exercises for back extensor muscles in healthy postmenopausal women demonstrated a significant increase in back extensor muscle strength and improvement of posture, but not bone mineral density (BMD).10 However, results of previous studies have been inconsistent; some have demonstrated improvement in muscle strength with exercise but not in BMD,3, 8, 13, 15, 23, 28 whereas others depicted improvement in muscle strength and BMD of the lumbar spine in estrogen-deficient women.14, 22

Subject compliance with prescribed exercise interventions presents a challenge. In one 3 year controlled, randomized study of healthy premenopausal women, the dropout rate was 34% in the exercise group and 22% in the control group.27 Even in studies of shorter duration (i.e., 2 year trial of brisk walking in postmenopausal women), 41% attrition was noted in both areas of the study.6 Subjects who are not self-motivated may not continue with prescribed exercise programs.20 However, compliance with a short-term exercise program has been more satisfactory.12

We hypothesized that: (1) stronger back muscles could reduce the risk of vertebral compression fractures; and (2) some of the muscle strength achieved through strengthening exercises may persist even several years after cessation.

The objective of this prospective study was to determine the long-term protective effect of stronger back muscles on the spine. In this controlled trial, 8 years after cessation of a 2 year course of back-strengthening exercises, we investigated whether increased muscle strength had any effect on the development of age-related changes such as muscle strength, BMD, or development of vertebral compression fractures.

Section snippets

Study population

Of 100 volunteers, 68 met the inclusion criteria.28 Later in the process of evaluation and enrollment, one subject withdrew because she was moving from the area, one withdrew for lack of interest, and one was hospitalized for hemorrhagic duodenal ulcer. Thus, 65 healthy white, postmenopausal, nonsmoking women were randomized and enrolled into a 2 year controlled, intensive, progressive back-exercise study (approved by our institutional review board). The average age of the subjects at the time

Results

Data for both study groups are summarized in Table 1. There were no dropouts from either group in the first 2 years of the study, and 77% of the subjects were available for follow-up at 10 years (27 of 34 BE subjects [79%] and 23 of 31 C subjects [74%]). On review of the subjects’ medical records and histories, none had had a hip fracture. All were nonsmokers with minimal or no alcohol intake. Although some of the subjects had been prescribed estrogen during the 8 year poststudy period, none

Discussion

In this study, we evaluated the long-term effect of stronger back muscles on the spine in estrogen-deficient women. The data showed that although vertebral bone loss was comparable in both groups, the BE group had fewer than half as many vertebral fractures as the control group, even 8 years after cessation of the back-strengthening exercises. The difference in BMD between the groups was not statistically significant at baseline nor at 2 year follow-up. However, at 10 year follow-up, even

Acknowledgments

This study was supported in part by Grant RR 00585 from the National Institutes of Health, a grant from the Retirement Research Foundation, and a grant from Donaldson Charitable Trust. The authors thank Sandy Fitzgerald for her efforts in contacting and scheduling the subjects for follow-up and for secretarial support.

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