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The purpose was to test the hypothesis that time to exhaustion and oxygen deficit in high-intensity exercise at a particular time of day would be influenced by training regularly at that time of day.Over a 5-wk period, 12 college-age women performed 20 high-intensity exercise training sessions. On Mondays, they performed four 2-min bouts of cycling at 2.5 W·kg-1 with 4-min recoveries; on Tuesdays and Thursdays, eight 1-min bouts at 3.0 W·kg-1 with 2-min recoveries; and on Wednesdays, three 3-min bouts at 2.2 W·kg-1 with 2-min recoveries. Six participants (a.m.-trained group) were randomly assigned to train in the morning (a.m.) and six others (p.m.-trained group) trained in the afternoon (p.m.). Upon completion of training, all participants were tested in both the a.m. and p.m. (random order) at the same times as training sessions had been scheduled. Tests involved exhaustive efforts at 2.6 W·kg-1.Results of a repeated measures ANOVA revealed a significant time of day of training × time of day of testing interaction effect on time to exhaustion (F1,10 = 8.29, P = 0.02). This suggested that the time of day of training affected the a.m.-p.m. pattern in time to exhaustion. Time to exhaustion for the a.m.-trained group was 398 ± 258 s in the a.m. test and 351 ± 216 s in the p.m. test (P = 0.07). The p.m.-trained group had significantly higher values in the p.m. test compared with the a.m. test (422 ± 252 s vs 373 ± 222 s;P = 0.03). There was also a significant interaction effect on oxygen deficit (F1,10 = 8.03, P = 0.02). This suggested that the time of day of training affected the a.m.-p.m. pattern in anaerobic capacity. Oxygen deficit for the a.m.-trained group was 64 ± 24 mL·kg-1 in the a.m. test and 50 ± 11 mL·kg-1 in the p.m. test (P = 0.10). The p.m.-trained group had significantly higher values in the p.m. tests (64 ± 24 mL·kg-1 vs 50 ± 11 mL·kg-1; P = 0.01) compared to the a.m. tests.These results demonstrate that there is temporal specificity in training to increase work capacity in high-intensity exercise. Greater improvements can be expected to occur at the time of day at which high-intensity training is regularly performed.