The purpose of this study was to determine if an exercise threshold existed in stimulating an elevation in bone mineral density (BMD), via resistance training, during the growth period in male rats. 27 male rats were randomly divided into Control (Con, n = 9), 3 ladder climb resistance trained group (3LC, n = 9), and 6 ladder climb resistance trained group (6LC, n = 9). The 3LC and 6LC groups were conditioned to climb a vertical ladder with weights appended to their tail 3 days/wk for a total of 6 wks, but the 6LC group performed significantly more work than the 3LC group. After 6 weeks, left tibial BMD (mean +/- SD) was significantly greater for 3LC (0.225 +/- 0.006 g/cm(2)) and 6LC (0.234 +/- 0.008 g/cm(2)) when compared to Con (0.202 +/- 0.013 g/cm(2)). Further, bone strength (force to failure in Newtons) was significantly greater for 3LC (132.7 +/- 13.7) and 6LC (130.0 +/- 22.8) compared to Con (102.0 +/- 10.1). There was no significant difference in BMD or bone strength between 3LC and 6LC. The results indicate that both resistance training programs were equally effective in elevating BMD and bone strength in growing rats. These data suggest that during growth, there is a stimulation threshold where more work per exercise session is ineffective in promoting additional bone formation.
Pierce, R. A., L. C. Lee, C. P. Ahles, S. M. Shdo, S. V. Jaque, and K. D. Sumida. "Different training volumes yield equivalent increases in BMD." International journal of sports medicine 31.11 (2010): 803-809. doi: 10.1055/s-0030-1262876
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