The Effect of Mode of Exercise on Fat Oxidation During Exercise

Abstract

The purpose of this study was to determine the difference in the relative intensity for peak fat oxidation for cycle er-gometer and treadmill exercise. Twenty subjects (8 men and 12 women; age, 26.26 ± 10.36 years; height, 171.18 ± 8.22 cm; mass, 77.25 ± 16.06 kg; percentage of body fat, 22.48 ± 9.04) completed a maximal graded exercise test on a treadmill (O2 peak = 41.36 ± 14.49 ml?kg−1?min−1 as well as a cycle ergometer (O2 peak = 36.45 ± 13.59 49 ml?kg−1?minr−1). Subjects also completed submaximal exercise protocols on the cycle (3-minute stage, 30 W increments) and the treadmill (3-minute stage, 0.5 m?h−1 increments). Recordings of O2, respiratory exchange ratio (RER), ratings of perceived exertion, and heart rate were recorded and averaged over the last 30 seconds of each stage. Calculations of total caloric expenditure and fat oxidation were made using the Lusk table. Peak fat oxidation was identified as the stage with the greatest number of fat kilocalories expended (reliability = .60). Relative O2 at the intensity for peak fat oxidation was compared between exercise modes using dependent means t-tests. Significance was set at p < 0.05. Results showed no differences in the relative intensities for peak fat oxidation for treadmill exercise (40.72 ± 14.07% O2 peak) versus cycle exercise (40.94 ± 9.60% O2 peak). RER was significantly higher with the cycle (0.87 ± 0.04) than with the treadmill (0.85 ± 0.04); however, this did not result in any difference in total calories (treadmill = 6.52 ± 3.70, cycle = 5.64 ± 2.15, p = 0.36) or fat calories (treadmill = 3.23 ± 1.54, cycle 2.36 ± 1.31, p = 0.06) expended at peak fat oxidation. The absolute O2 at peak fat utilization was 11% higher with treadmill exercise, but this mirrored differences in peak. We conclude that for both treadmill and cycle exercise, maximal fat calorie expenditure will occur around 40% of peak without significant differences in fat calorie expenditure.