BACKGROUND: Muscle degrades fat and carbohydrate (CHO) during exercise to meet the demand for ATP. Factors including exercise intensity/duration and fitness level are recognized as primary determinants of the relative contribution of these macronutrients to substrate metabolism, although exercise mode has also been identified. The aim of this study was to determine potential differences in substrate metabolism during treadmill (TM) and cycle ergometer (CE) exercise performed at equal rating of perceived exertion (RPE). METHODS: Eleven recreationally active women (age =23.0±3.0 yr, Body Mass Index =20.7±1.7 kg/m2) performed one 30 min bout of endurance exercise on the CE and TM separated by 1 wk. Three 10 min stages of exercise were completed at RPE equal to 11, 13, and 15. During exercise, gas exchange data were continuously obtained to determine fat and CHO oxidation. Subjects fasted 3 h prior to exercise and standardized their dietary intake 48 h prior to each bout. Two-way ANOVA with repeated measures was used to determine differences in respiratory exchange ratio (RER) and fat and CHO oxidation between exercise modes. RESULTS: RER was higher (P<0.05) during CE compared to TM at RPE equal to 11 (0.92±0.03 vs. 0.87±0.06), 13 (0.95±0.03 vs. 0.89±0.05), and 15 (1.00±0.03 vs. 0.93±0.04), leading to lower fat oxidation (P=0.009) and higher CHO oxidation in response to TM versus CE (P=0.003). CONCLUSIONS: Greater fat utilization occurred in response to treadmill walking at RPE ranging from 11-15 versus cycle ergometry.
BACKGROUND: Muscle degrades fat and carbohydrate (CHO) during exercise to meet the demand for ATP. Factors including exercise intensity/duration and fitness level are recognized as primary determinants of the relative contribution of these macronutrients to substrate metabolism, although exercise mode has also been identified. The aim of this study was to determine potential differences in substrate metabolism during treadmill (TM) and cycle ergometer (CE) exercise performed at equal rating of perceived exertion (RPE). METHODS: Eleven recreationally active women (age =23.0±3.0 yr, Body Mass Index =20.7±1.7 kg/m2) performed one 30 min bout of endurance exercise on the CE and TM separated by 1 wk. Three 10 min stages of exercise were completed at RPE equal to 11, 13, and 15. During exercise, gas exchange data were continuously obtained to determine fat and CHO oxidation. Subjects fasted 3 h prior to exercise and standardized their dietary intake 48 h prior to each bout. Two-way ANOVA with repeated measures was used to determine differences in respiratory exchange ratio (RER) and fat and CHO oxidation between exercise modes. RESULTS: RER was higher (P<0.05) during CE compared to TM at RPE equal to 11 (0.92±0.03 vs. 0.87±0.06), 13 (0.95±0.03 vs. 0.89±0.05), and 15 (1.00±0.03 vs. 0.93±0.04), leading to lower fat oxidation (P=0.009) and higher CHO oxidation in response to TM versus CE (P=0.003). CONCLUSIONS: Greater fat utilization occurred in response to treadmill walking at RPE ranging from 11-15 versus cycle ergometry.