In premenopausal women, a number of intervention studies have reported that high-intensity PRT (three sets of 8–12 repetitions, 12–14 exercises, 70–85% of 1 RM;where 1 RM is the maximal weight that can be moved one time only) performed three times per week can increase lumbar spine and hip BMD by up to 2% after 12 to 18 months of training [144,153]. However, the skeletal responses to PRT may depend on the intensity and frequency of training. For instance, Warren et al. reported no significant effect of 2 years of PRT performed twice a week (three sets of 8–10 repetitions using variable resistance machines and free weights that stressed all major muscle groups) on proximal femur or lumbar spine
BMD, with the exception that femoral neck BMC was preserved compared to controls, suggesting that there may have been an exercise-induced increase in bone size [160]. The lack of a marked effect in this study may also be due to the fact that the training was largely unsupervised and strength gains for the upper and lower body were minimal (5–10%). Thus, the progressive loading required to induce skeletal gains may have been less than optimal. Indeed, in a meta-analysis of RCTs in premenopausal women high-intensity PRT was shown to be efficacious in increasing BMD at the lumbar spine by
approximately 1%, but not the femoral neck [164].