Introduction/Objective: The spate of literature on the topic of osteoporosis reflects the impact of this disease nowadays. With the ageing of the population, the medical and social costs of skeletal fragility leading to fractures is certain to grow, unless effective prophylactic and therapeutic regimens can be developed. Exercise is suggested as such a possible regimen against involutional bone loss. Various clinical trials examining the effects of exercise training programs on the bone mass have been reported and provide mixed results. The purpose of the present meta-analysis is to address a quantitative review of the randomized controlled trials (RCTs) on the effects of exercise training programs on the bone mass, measured as bone mineral density (BMD), of the lumbar spine (LS) and the femoral neck (FN) in pre- and postmenopausal women.
Methods: The literature from 1966 through January 1997 was searched for published RCTs on the effects of exercise training programs on BMD of LS and FN. Studies were selected if they met the criteria for RCT according to the Cochrane Collaboration, and if the training program had a minimal length of 16 weeks and data representation was adequate. Studies were obtained from computer searches (MEDLINE), as well as hand-searches, and cross-referencing. Study treatment effect is defined as the difference between %change in BMD per year in the training group and in the control group. Summary estimates with the 95%-confidence intervals (95%CI) of these treatment effects were calculated using inverse-variance weighting. This weighting method results in large contributions of studies with large sample sizes and small standard deviations. Separate meta-analyses were performed for pre- and postmenopausal women. In addition, for the postmenopausal women it was possible to perform separate analyses for strength and endurance training programs.
Results: Seventeen articles with RCTs were included, which yielded 20 studies in LS and 13 studies in FN. The training caused significant summary treatment effects in both pre-menopausal women (LS: 0.91%/y, 95%CI: 0.44 to 1.37 and FN: 0.90%/y, 95%CI: 0.29 to 1.50) and postmenopausal women (LS: 0.86%/y, 95% CI: 0.43 to 1.29 and FN: 0.97% 0.44 to 1.50). The separate analyses for training type in postmenopausal women showed that the summary treatment effects of the endurance training programs were significant in both LS (0.96%/y, 95%CI: 0.43 to 1.49) and FN (0.99%/y, 95%CI: 0.38 to 1.59), but that the strength training did not result in significant summary treatment effects (LS: 0.75%/y, 95%CI: -0.04 to 1.54; FN: 0.91%/y, 95%CI: -0.15 to 1.97).
Discussion: Exercise prevents almost 1% bone loss per year in both pre- and post-menopausal women. The separate analyses for training type in the post-menopausal women showed that the effect of strength training, in contrast with endurance training, does not reach statistical significance.