This study was designed to determine the effect of duration (30, 45, 60 min) of exercise at 70% VO2 max on oxygen consumption during the exercise and post-exercise periods and if the post-exercise oxygen consumption (EPOC) is related to elevated tympanic temperature. Two male and three female volunteer subjects cycled at 70% VO2 max for 30, 45 and 60 min. The EPOC increased 2.35 and 5.3 fold when exercise duration was increased from 30 to 45 min and from 30 to 60 min respectively. The time for VO2 to return to resting levels following exercise was 128 +/- 4.4 min, 204 +/- 15.9 min and 455 +/- 30.0 min after the 30, 45 and 60 min exercise bouts. Tympanic temperatures were stable at 38.6 degrees C after approximately 30 min of exercise, but all had fallen to resting conditions approximately two hours post-exercise. The correlation between core temperature and EPOC, and RER and EPOC, was r = 0.64-0.75 and r = 0.86-0.89, respectively. These data emphasize the importance of extending the work time for elevating the energy cost during and post-exercise, and suggest that the EPOC can be explained in part by the effects of elevated temperature and metabolic substrate.