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 Â-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.

The results suggest that during growth, a low amount of resistance exercise was just as effective as high volumes of strength training for stimulating bone modeling.

The purpose of this study was to determine the existence of sex differences in the resistance training-induced elevation in bone mineral density (BMD) and bone strength (Fmax) during the growth period in rats. 16 male (M) and 16 female (F) rats (approx. 8 weeks old) were randomly divided into sedentary control (MC=8, FC=8), and resistance-trained (RT) groups (M-RT=8, F-RT=8). The RT groups were conditioned to climb a vertical ladder 4 consecutive times (per exercise session) with weights attached to their tail 3 days per week for a total of 6 weeks. After 6 weeks, there were no interaction effects (sex×exercise). The main effect of sex indicated no difference in tibial BMD (in g/cm(2)) for males (0.226±0.005) compared to females (0.221±0.004). However, Fmax (in Newtons) was significantly greater for males (131.3±5.3) compared to females (89.9±3.0). The main effect of exercise indicated that tibial BMD and Fmax were significantly greater for RT groups (0.234±0.004 g/cm(2) and 120.9±7.4 Newtons) compared to controls (0.212±0.003 g/cm(2) and 100.3±5.1 Newtons). The results indicate that during growth, there were no sex differences in the training-induced elevation in BMD and bone mechanical properties.

The purpose of this study was to determine if there was a sex difference in the resistance training‐induced elevation in bone mineral density (BMD) during the growth period in rats. Sixteen male and 16 female rats (~8wks old) were randomly divided into Control (MC=8, FC=8), and resistance trained (RT) groups (M‐RT= 8, F‐RT=8). The RT groups were conditioned to climb a vertical ladder 4 consecutive times (per exercise session) with weights appended to their tail 3 days/wk for a total of 6 wks. After 6 wks, left tibial BMD (in g/cm2) was significantly greater for M‐RT (0.240 ± 0.005) compared to MC (0.211 ± 0.005). Further, bone strength (force to failure in Newtons) from the right tibia was significantly greater for M‐RT (144.4 ± 8.0) compared to MC (118.3 ± 2.7). In contrast, while the BMD for F‐RT (0.226 ± 0.006) was elevated compared to FC (0.214 ± 0.005), statistical significance was not achieved (P=0.09) whereas bone strength was significantly greater (P=0.04) for F‐RT (97.4 ± 3.5) compared to FC (82.3 ± 3.1). While the impact of resistance training demonstrated anticipated trends for BMD and bone strength among males and females, the training‐induced elevations were greater for M‐RT compared to F‐RT. The results indicate that the resistance training program was more effective for elevating BMD and bone strength in males compared to females during the growth period in rats.

The purpose of this study was to determine if there was an exercise threshold 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 where the 6LC group performed significantly more work compared to the 3LC group. After 6 wks, left tibial BMD (in g/cm2) was significantly greater for 3LC (0.225 ± 0.002) and 6LC (0.234 ± 0.003) compared to Con (0.202 ± 0.004). Further, bone strength (force to failure in Newtons) was significantly greater for 3LC (132.7 ± 4.6) and 6LC (130.0 ± 7.6) compared to Con (102.0 ± 3.4). Serum osteocalcin (OC in ng/ml, a marker for osteoblast activity) was significantly greater for 3LC (50.5 ± 3.4) and 6LC (41.7 ± 2.6) compared to Con (25.0 ± 3.4). There was no significant difference in BMD, bone strength, or OC 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.