This study examined the efficacy of two different resistance training programs in enhancing bone modeling and bone mineral density (BMD) in maturating rats. One exercise mode involved lifting a lighter weight with more repetitions (LI), while the other regimen involved lifting a heavier weight with fewer repetitions (HI) where the total volume of work between exercise programs was equivalent by design. Twenty-three male rats were randomly divided into control (Con, n = 8), LI (n = 7), and HI (n = 8) groups. The LI and HI groups were conditioned to climb a vertical ladder with weights appended to their tail 4 days/wk for 6 wks. After training, serum osteocalcin (OC) was significantly (p < 0.05) higher in both HI (45.2 +/- 1.7 ng/ml) and LI (39.1 +/- 2.2 ng/ml) when compared to Con (29.9 +/- 0.9 ng/ml). Left tibial BMD was significantly (p < 0.05) greater for HI (0.231 +/- 0.004 g/cm (2)) when compared to both LI (0.213 +/- 0.003 g/cm (2)) and Con (0.206 +/- 0.005 g/cm (2)) with no significant difference between LI and Con. The results indicate that both HI and LI are effective in elevating serum OC, implicating an osteogenic response; however, only HI resulted in a significant elevation in BMD.