Fat oxidation in cold environments and carbohydrate (CHO) use in hot environments are increased during exercise at steady-state submaximal workloads. However, the influence of cold and heat on fat and CHO oxidation curves remain unknown. We therefore examined the influence of a cold and warm ambient temperature on fat and CHO oxidation across a wide range of exercise intensities during treadmill and cycle ergometer exercise. Nine, young, healthy, male subjects completed four trials, during which they performed an incremental peak oxygen consumption (⩒O_2peak) test on a cycle ergometer or treadmill in a 4.6°C or 34.1°C environment. Substrate oxidation, maximal fat oxidation rate (MFO), and exercise intensity where MFO occurs (Fat_max) were assessed via indirect calorimetry. MFO was significantly greater in the cold vs. warm during the treadmill exercise (0.66 ± 0.31 vs. 0.43 ± 0.23 g min^-1; p = 0.02) but not during cycling (0.45 ± 0.24 vs. 0.29 ± 0.11 g min^-1; p = 0.076). MFO was also greater during treadmill vs. cycling exercise, irrespective of ambient temperature (0.57 g min^-1 vs. 0.37 g min^-1; p = 0.04). Fat_max was greater in the cold vs. warm for both treadmill (57 ± 20 vs. 37 ± 17%⩒O_2peak; p = 0.025) and cycling (62 ± 28 vs. 36 ± 13%⩒O_2peak; p = 0.003). Multiple, linear, mixed-effects regressions revealed a strong influence of ambient temperature on substrate oxidation. We demonstrated that exercising in a cold environment increases MFO and Fat_max, predominantly during treadmill exercise. These results validate the implication of ambient temperature on energy metabolism over a wide range of exercise intensities.

Lina Perrier

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