Brown, GA, Cook, CM, Krueger, RD, and Heelan, KA. Comparison of energy expenditure on a treadmill vs. an elliptical device at a self-selected exercise intensity. J Strength Cond Res 24(6): 1643-1649, 2010-Treadmills (TM) and elliptical devices (EL) are popular forms of exercise equipment. The differences in the training stimulus presented by TM or EL are unknown. The purpose of this investigation was to evaluate oxygen consumption, energy expenditure, and heart rate on a TM or EL when persons exercise at the same perceived level of exertion. After measuring peak oxygen uptake (V̇O2peak) in 9 male and 9 female untrained college-aged participants, the subjects performed 2 separate 15-minute submaximal exercise tests on the TM and EL at a rating of perceived exertion (RPE) of 12-13. V̇O2peak was higher (p < 0.05) in the males (48.6 ± 1.5 vs. 45.2 ± 1.6 ml/kg/min) than the females (41.7 ± 1.8 vs. 38.8 ± 2.2 ml/kg/min) for both TM and EL (means ± standard error of the mean; for TM vs. EL respectively), but there were no differences in the measured V̇O2peak between TM or EL. During submaximal exercise there were no differences in RPE between TM and EL. Total oxygen consumption was higher (p < 0.05) in males (30.8 ± 2.2 vs. 34.9 ± 2.2 L) than females (24.1 ± 1.8 vs. 26.9 ± 1.7 L) but did not differ between TM and EL. Energy expenditure was not different between TM (569 ± 110 J) or EL (636 ± 120 kJ). Heart rate was higher (p < 0.05) on the EL (164 ± 16 beats/min) compared to the TM (145 ± 15 beats/min). When subjects exercise at the same RPE on TM or EL, oxygen consumption and energy expenditure are similar in spite of a higher heart rate on the EL. These data indicate that during cross training or noncompetition-specific exercise, an elliptical device is an acceptable alternative to a treadmill.