Metabolic Responses to Acute Exercise at Two Different Exercise Intensities during Rowing and Cycling Ergometry

Abstract

The relative contribution of carbohydrate and fat oxidation to whole body energy production during steady state exercise is dependent on exercise intensity and duration i.e. fat oxidation declines with increasing exercise intensity. However, exercise that requires a greater active muscle mass may also influence substrate utilisation by increasing the contribution of fat oxidation at the same relative intensity (%VO2peak). PURPOSE: The purpose of this study was to determine the impact of whole body (rowing) and lower limb (cycling) exercise on substrate utilisation at different exercise intensities. METHODS: Nine trained rowers [age, 23.3 ± 1.7yrs; body mass, 75.9 ± 1.9 kg; height, 1.81 ± 0.02 m] exercised for 20-min at 50%VO2peak followed by 20-min at 4mM lactate threshold, once each on a rowing (ROW) and cycling (CYC) ergometer. Steady state carbohydrate and fat oxidation rates were determined by indirect calorimetry during the last 10-min of each stage. RESULTS: Oxygen consumption during exercise at 50% VO2peak was similar between ROW and CYC (2.06 ± 0.12 vs. 2.01 ± 0.10 l.min−1; p=0.555). The steady state rates of carbohydrate oxidation (1.50 ± 0.13 vs. 1.57 ± 0.06 g.min−1; p=0.496) and fat oxidation (0.42 ± 0.04vs. 0.36 ± 0.04 g.min−1; p=0.409) were also similar for ROW and CYC at this intensity. During exercise at 4mM lactate threshold, oxygen consumption was greater in the ROW trial (3.66 ± 0.21 vs. 3.10 ± 0.16 l.min−1; p=0.014). However, the relative contribution of carbohydrate and fat to whole body energy production was similar between modes (fat contribution: 18.8 ± 2.9% vs. 16.4 ± 2.2%, ROW vs. CYC respectively; p=0.576). There were slightly, but not significantly, higher rates of carbohydrate (3.65 ± 0.31 vs. 3.15 ± 0.14 g.min−1; p=0.139) and fat (0.34 ± 0.06 vs. 0.27 ± 0.05 g.min−1; p=0.359) oxidation during ROW. CONCLUSION: At both 50% VO2peak and LT, the contribution of carbohydrate and fat oxidation to energy production was similar during rowing and cycling. During steady state exercise, recruiting a greater muscle mass does not appear to alter the contribution of fat oxidation to energy production at the same relative intensity or with a similar level of metabolic stress.