To determine muscle adaptations to retraining after short-term detraining, we examined the effects of continuous and interrupted resistance training on muscle size and strength in previously untrained men. Fifteen young men were divided into continuous training (CTr) or retraining (RTr) groups and performed high-intensity bench press training. The CTr group trained continuously for 15 weeks, while the RTr group trained for 6 weeks, stopped for a 3-week detraining period and resumed training at week 10. After the initial training phase, increases (P<0·01) in one repetition maximum (1-RM) and magnetic resonance imaging-measured triceps brachii and pectorals major muscle cross-sectional areas (CSAs) were similar in both groups. Muscle CSA and 1-RM increased (P<0·05) continuously for the CTr group, but the muscle adaptations were lower (P<0·05) after the last 6-week training period than after the initial phase. In the RTr group, there were no significant decreases in muscle CSA and 1-RM after the 3-week detraining period, and increases in muscle CSA after retraining were similar to those observed after initial training. Ultimately, improvements in 1-RM and muscle CSA in both groups were similar after the 15-week training period. Our results suggest that compared with continuous 15-week training, 3-week detraining does not inhibit muscle adaptations.