2085 Resistance exercise is a potent stimulus for acute increases in the anabolic hormone concentrations such as growth hormone (GH) and testosterone (Kraemer et al., 1990; Goto et al., 2003). However, it is not clear whether acute increases in hormonal concentrations play a role in enhancements of muscular strength and muscle volume. PURPOSE: We investigated the effects of magnitude of hormone responses to a single bout of resistance exercise session on muscular adaptations during prolonged training program. METHODS: Twenty-six male subjects (19–27 years) were assigned to either “no-rest group (NR)”, “rest group (R)” and “control group”. Training regimen in the NR- group consisted of 5 sets at 10 repetition maximum (RM) with 1-min rest periods between sets. In the regimen of R-group, subjects rested for 30 s immediately after 5 repetition in each set. NR- and R-groups performed three exercises (lat pulldown, shoulder press and bilateral knee extension) at the same number of lifts (with or without intra-set rest) at the same relative intensity two days per wk for 12 wk. Acute hormonal responses to each regimen were initially assessed, and then muscular strength, endurance and cross sectional area (CSA) were determined before and after training period. RESULTS: In the regimen of NR-group, concentrations of blood lactate, serum GH, plasma adrenaline and noradrenaline showed marked increases after acute exercise, whereas those in the R-group did not. Changes in muscular strength (1RM, isometric and isokinetic strength) and endurance were significantly greater in NR-group than in R-group (p < 0.05). CSA of the quadriceps femoris also showed a significantly greater increase in NR-group (12.8 ± 1.3 %) than in R-group (4.0 ± 1.2 %; p < 0.01). Furthermore, significant correlation was observed between peak value of post-exercise GH concentration and change in CSA after 12 wk of training (r = 0.672, p < 0.05). In the control group, no significant change was observed in all variables. CONCLUSION: These results suggest that the magnitude of acute GH response may be important for anabolic adaptations during resistance training in young men. Supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (C), 15500426, 2003 (Japan).