Detraining Reverses Positive Effects of Exercise on the Musculoskeletal System in Premenopausal Women

Abstract

We studied the effects of a 6-month withdrawal of exercise after 12 months of progressive impact (jump) plus lower body resistance training on risk factors for hip fracture in premenopausal women (age, 30 -45 years). Twenty-nine women completed the 12-month training and detraining programs and were compared with 22 matched controls. Bone mineral density (BMD) at the greater trochanter, femoral neck, lumbar spine, and whole body and body composition (% body fat) were measured by dual energy X-ray absorptiometry (DXA; Hologic QDR-1000/W). Knee extensor and hip abductor strength were assessed via isokinetic dynamometry (Kin-Com 500H); maximum leg power was tested using a Wingate Anaerobic Power test; and dynamic postural stability was measured on a stabilimeter (Biodex). All measurements were conducted at baseline, 12 months and 18 months with an additional midtraining measurement of BMD. Exercisers trained three times per week in a program of 100 jumps and 100 repetitions of resistance exercises at each session. Intensity was increased using weighted vests to final values of 10% and 13% of body weight (BW) for jump and resistance exercises, respectively. Differences between groups from training were analyzed by repeated measures analysis of covariance (ANCOVA), adjusted for baseline values. Detraining effects were analyzed by comparing the changes from training with the changes from detraining using repeated measures analysis of variance (ANOVA). Baseline values were not significantly different between exercisers and controls. Percent change over the training period was significantly greater in the exercise group than in the control group at the greater trochanter (2.7 ؎ 2.5% vs. 0.8 ؎ 0.8%, respectively; p < 0.01) and approached significance at the femoral neck (1.2 ؎ 3.2% vs. ؊0.3 ؎ 1.9%, respectively; p ‫؍‬ 0.06). Significant improvements also were observed in exercisers versus controls for strength and power with exercisers increasing 13-15% above controls, whereas stability was not different between groups. After 6 months of detraining, BMD and muscle strength and power decreased significantly toward baseline values, whereas control values did not change. We conclude that the positive benefits of impact plus resistance training on the musculoskeletal system in premenopausal women reverse when training is withdrawn. Therefore, continued training, perhaps at a reduced frequency and intensity, is required to maintain the musculoskeletal benefit from exercise that may lower fracture risk in later life. (J Bone Miner Res 2000;15:2495-2503)

Reduced Training Is Associated With Increased Loss of BMD

“…However, published studies predominantly include elderly subjects with low exercise-induced BMD benefits or shorter follow-up period. (33)(34)(35)45) In this study, the long-term retired athletes still had a 5.1 percentage point higher BMD in the leg at follow-up after close to two decades of retirement in comparison with the controls, despite the reduction in the residual high BMD at most sites. Possible explanations for this finding may be that the athletes in this study had reached a much higher BMD during the period of high physical activity, that they had been active longer, that they had started exercising at an earlier age, and that they had exercised at a high level in comparison with the exercisers in previously cited studies.…”

“…At present, no conclusive answers can be obtained from published longitudinal data, because studies report both that BMD benefits are maintained with cessation of activity (27)(28)(29)(30)(31)(32) and that BMD benefits are lost with retirement. (33)(34)(35)(36)(37)(38) Because all prospective studies are short-term reports, catching only a short period of retirement, we must wonder if the retirement period might have been too short to capture a faster BMD loss compared with controls. Until now, there are no prospective controlled studies following young girls from intense activity into a retirement period exceeding 5 years.…”

The Effect of Detraining on Bone

“…Studies of the effect of detraining on weight bearing bones in premenopausal women have yielded inconsistent data [28][29][30][31][32][33] (Table 1). A cross-sectional retrospective study of former athletes was performed by Kahn et al [34], who examined a cohort of 101 retired ballet dancers with a mean age of 51 years compared to 101 controls matched for menopausal status, age, height, and weight.…”

“…Both groups had significant declines in BMDs of the femoral neck, Ward's triangle, and greater trochanter, but only gymnasts had a significant decline in lumbar spine BMD. In addition, randomized controlled studies have indicated that there is a detraining effect on BMD in premenopausal women [29,32]. Winters et al investigated in a randomized controlled study the effect of 6 months of detraining after a 12-month jumping and resistance program in premenopausal women aged 30-45 years [29].…”

“…In addition, randomized controlled studies have indicated that there is a detraining effect on BMD in premenopausal women [29,32]. Winters et al investigated in a randomized controlled study the effect of 6 months of detraining after a 12-month jumping and resistance program in premenopausal women aged 30-45 years [29]. They found that the percent change over the training period was significantly greater in the exercise group than in the control group for the greater trochanter and approached a significant difference for the femoral neck.…”