BACKGROUND The aim of this study was to investigate the influence of excessive training on exercise performance and physiological and psychological parameters. METHODS Eight physically active males (age, mean±standard deviation [SD]: 23±3 years) completed 3 weeks of an intervention program consisting of normal (N), intensified (IT), and recovery (R) training phases (7 days for each phase). Physiological and psychological parameters were measured at rest before the intervention (Pre), and every Monday, Wednesday, and Saturday (day 1, day 3, day 6, respectively), and exercise performance tests were performed before the intervention (Pre) and every Saturday (day 6) during the intervention period. RESULTS The estimated energy expenditure during a training session revealed a more than two-fold increase from the N phase to the IT phase. During the IT phase, augmented training volume significantly affected the POMS (fatigue) and motivation towards training (P<0.05) scores, and these values returned to baseline levels during the R phase. Moreover, resting serum testosterone concentrations significantly decreased and exercise-induced cortisol responses were diminished during the IT phase (P<0.05). The altered endocrine responses were still observed during the subsequent R phase. Resting serum BAP levels (an index of antioxidant potential) significantly increased during the N phase (P<0.05). Meanwhile, there was no significant change in exercise performance, resting d-ROM (an index of oxidative stress) values, or salivary amylase activity. CONCLUSIONS Increases in training stress altered psychological parameters, resting testosterone concentrations, and exercise-induced cortisol responses. Exercise performance did not correlate with training stress, suggesting that monitoring endocrine and psychological parameters is essential during intensified training periods.