Fat Oxidation Rates are Higher Over a Wide Range of Intensities in Rowing Compared to Cycling Ergometry

Abstract

The relative contribution of carbohydrate and fat oxidation to whole body energy production during exercise is dependent on oxygen availability. Continuous incremental exercise is associated with a progressive increase in carbohydrate oxidation and a decrease in fat oxidation. The exercise modality, more specifically the muscle mass recruited, is also thought to be an important contributor to substrate selection. PURPOSE: The purpose of this study was to determine the rates of fat oxidation and the cross-over point for substrate utilisation over a wide range of intensities during incremental rowing and cycle ergometry. METHODS: Thirteen moderately trained male rowers [age, 23.2 ± 1.6 yrs; height, 1.82 ± 0.02 m; body mass, 77.0 ± 1.6 kg] performed a continuous incremental exercise test to exhaustion on an electronicaly braked cycle ergometer and an air braked rowing ergometer. The exercise intensity began at 95W and increased in 35W increments every 3-min. Rates of substrate oxidation and the relative contribution to energy expenditure were calculated for the same absolute (W) and relative (%VO2peak) intensity by indirect calorimetry during the last 2-min of each 3-min stage. RESULTS: Peak oxygen consumption was similar for the rowing (57.5 ± 1.5 ml kg min−1) and cycle (55.7 ± 1.6 ml kg min−1) ergometer tests. Peak fat oxidation was higher in rowing (0.72 ± 0.05 g.min−1) than cycling (0.51 ± 0.04 g.min−1, p=0.008) and occurred during the first stage. The rate of fat oxidation was greater during rowing at the same absolute (p=0.019) and relative (p=0.001) exercise intensities up to ∼93%VO2peak. The crossover point for substrate utilisation occurred at a higher relative exercise intensity for rowing than cycling (57.8 ± 2.1 vs. 42.1 ± 3.6 %VO2peak, p=0.003). CONCLUSION: The rate of fat oxidation is higher during rowing exercise than cycling, across a range of exercise intensities, despite similar oxygen uptake. It is possible that the greater muscle mass recruited during rowing may distribute the metabolic stress and facilitate fat oxidation. These results indicate that when prescribing exercise to optimise fat oxidation, the exercise modality should be such that it recruits a larger muscle mass.