Abstract:The purpose of this meta-analysis is calculating the summary effects of (randomized) controlled trials examining the effects of endurance (with weight bearing and aerobic activities) and strength training programs (with high impact and resistance activities) on the bone mineral density (BMD) of the lumbar spine (LS) and the femoral neck (FN) in postmenopausal women. Studies were selected if they met the criteria of randomized controlled trials (RCT's) and controlled trials (CT's) according to the Cochrane collaboration, and if the training programs had a minimal length of 16 weeks, that is needed to result in measurable changes in BMD. The effect of exercise training was defined as the difference between the percentage change in BMD per year (%change/y) in the training group and in the control group. Summary estimates with the 95% confidence intervals (95% CI) of these training effects were calculated using inverse-variance weighting (resulting in larger contributions of studies with large sample sizes and smaller standard deviations). In total 22 RCT's were included and 13 CT's. No indication was found for a systematic influence of RCT's with non-significant or smaller treatment effects. The endurance training caused significant summary effects of the RCT's in both the LS (0.96 %change/y; 95%CI: 0.43 to 1.49) and in the FN (0.90 %change/y; 95%CI: 0.29 to 1.51). The strength training however caused no significant summary effects in both the LS (0.67 %change/y; 95%CI: -0.08 to 1.41) and in the FN (0.86%change/y; 95%CI:-0.18 to 1.91). The endurance training caused significant summary effects of the CT's in both the LS (2.11 %change/y; 95%CI: 1.24 to 2.99) and in the FN (1.86 %change/y; 95% CI: 0.80 to 2.91). Only one CT was found with a strength-training program and therefore no summary training effects could be estimated. Strength training programs of RCT's in postmenopausal women show training effects that are lower (0.7 %change/y) than endurance training programs (1.0 %change/y). The CT's resulted in endurance training effects that are about twice as high (2.0 %change/y) which is an indication of the confounding effect introduced by the non-random allocation of the subjects. This meta-analysis shows that exercise training has the potential to prevent or reverse the bone loss in postmenopausal women by almost 1% per year. Reference: Wolff I, Croonenborg JJ van, Kemper HCG, Kostense PJ, Twisk JWR et al. The effects of exercise training programs on the bone mass; a meta-analysis of published controlled trials in pre- and post menopausal women. Ost Int; 1999.