To study the effects of exercise training with eccentric muscle contractions on body temperatures, energy cost, and performance capacity, six human subjects were tested before and after a 5-week training program of eccentric exercise. Exercise was performed as leg cycling on a motor-driven ergometer at power levels ranging 252-316 W. Training consisted of three sessions/week for 1 h/session. As a result of the training, VO2, fH, and mean skin temperature were lowered for each subject at the same absolute exercise intensities. Ability to continue exercise as indicated by endurance time improved with training. Before training, four subjects terminated exercise after 30 min because of localized leg exhaustion and one subject could not continue longer than 45 min. After training, all six subjects completed 45 min of the exercise test without difficulty. Esophageal and muscle temperatures evidenced no changes as a result of training. It was concluded that the inability of subjects to perform eccentric exercise in the untrained state was not related to muscle temperature.