Leptin and osteocalcin play a role in the regulation of the fat-bone axis and may be altered by exercise. To determine if osteocalcin reduces fat mass in humans fed ad libitum and if there is a gender dimorphism in the serum osteocalcin and leptin responses to strength training, we studied forty-three male (age 23.9±2.4 years, mean ± SD) and twenty-three female physical education students (age 23.2±2.7 years). Subjects were randomly assigned to two groups: training (TG) and control (CG). TG followed a strength combined with plyometric jumps training program during nine weeks, while the CG did not train. Physical fitness, body composition (DEXA) and serum concentrations of hormones were determined pre- and post-training. In the whole group of subjects (pre-training) the serum concentration of osteocalcin was positively correlated (r=0.29-0.42, P<0.05) with whole body and regional bone mineral content (BMC), lean mass, dynamic strength and serum free testosterone concentration (r=0.32). However, osteocalcin was negatively correlated with leptin concentration (r=-0.37), fat mass (r=-0.31) and the % body fat (r=-0.44). Both genders experienced similar relative improvements in performance, LM (+4-5%) and whole body (+0.78%) and lumbar spine BMC (+1.2-2%) with training. Serum osteocalcin concentration was increased after training by 45 and 27% in men and women, respectively (P<0.05). Fat mass was not altered by training. Vastus lateralis myosin type II heavy chain composition at the start of the training program predicted 25% of the osteocalcin increase after training. Serum leptin concentration was reduced with training in women. In summary, while the relative effects of strength training+plyometric jumps in performance, muscle hypertrophy and osteogenesis are similar in men and women, serum leptin concentration is reduced only in women. The osteocalcin response to strength training is in part modulated by the muscle phenotype (MHC isoform composition). Despite the increase in osteocalcin fat mass was not reduced.