The purpose of this study was to determine the physical and physiologic changes induced by 9 weeks of equivalent amounts of high‐intensity running (n = 8) and cycle ergometer training (n = 8) on treadmill maximal oxygen uptake (YO2max), cycle ergometer peak VO2, a 1609 m (1.0 mile) running time, and a submaximal treadmill running VO2, heart rate, and accumulated lactate concentration in normal young men ages 25.1±1.2 years (mean±SE). Subjects began by training 4 days per week at 75 to 80% maximum heart rate (MHR) and during weeks 3 to 9 they exercised at 80 to 85% MHR. Interval training at 90 to 95% MHR was also added 2 days per week (total of 40 to 45 minutes). Both groups significantly (p≤s 0.01) improved treadmill VO2rnaxand cycle ergometer peak VO2. There was no difference in the amount of improvement between the groups on each test. For the cycle‐trained group, mean percent increases in peak VO2maximprovement on the treadmill and cycle ergometer were similar, whereas the running group mean percent change on the same tests showed a significant (p≤0.05) superior gain on the treadmill. Group mean running time significantly improved (p≤0.01) for both groups; however, a significant between‐group interaction (p≤0.05) for the 1609 m run indicated a differential effect on the magnitude of change favoring the running group. Results indicate that 9 weeks of equivalent intensity cycle training may be utilized as a substitute for running training with a relatively similar gain in treadmill‐and cycle ergometer‐tested aerobic power.