, Volume 55, Issue 1, pp 59-67

Effects of unilateral strength training and detraining on bone mineral density and content in young women: A study of mechanical loading and deloading on human bones

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Abstract

This study assessed the effect of unilateral strength training at 80% one repetition maximum and of detraining on bone mineral density (BMD, g/cm-2) and bone mineral content (ΣBMC, g) in young women. Twelve female physiotherapy students trained their left limb by leg press an average of four times per week for 1 year followed by 3 months of detraining. Twelve students served as controls. Repeated bone measurements were performed by dual energy X-ray absorptiometry of the lumbar spine, femoral neck, distal femur, patella, proximal tibia, and calcaneus. The training increased the muscle strength of the trained limb, and the BMD of the same limb showed a nonsignificant but systematic increase in distal femur, patella, and proximal tibia, and in ΣBMC of the five measured limb sites (considered an index of the total osteogenic effectiveness of the training). Simultaneously, the muscle strength increased in the untrained limb as an evidence of cross-training effect. A corresponding small but systematic increase was also seen in BMD of this limb as well as in ΣBMC. After the cessation of training, leg extension strength was retained but BMD and ΣBMC of the trained and untrained limbs declined towards baseline values in 3 months. The BMD and ΣBMC values in the control group showed an increasing tendency during the follow-up but the changes were less than 1%. The differences of the changes in BMD and ΣBMC between the left and right limb in the control group, as well as between the same limb in the training and control groups were nonsignificant. The findings of this study indicate that unidirectional strength training, intensive enough to induce substantial strength gain, is not an effective stimulus to increase BMD and BMC in young, physically active women. The unilateral training model turned out to be feasible in these subjects, producing a definite cross-training effect in muscle strength and a trend of similar effect in BMD. Further development of the unilateral training model, and studies to test if training produces adaptation in nonloaded bones (i.e., a crosstraining effect), are also warranted.