Effect of ambient temperature on fat oxidation during an incremental cycling exercise test

Abstract

Aim: The objective of this current research was to compare fat oxidation rates during an incremental cycling exercise test in a temperate vs. hot environment.

Methods: Twelve healthy young participants were recruited for a randomised crossover experimental design. Each participant performed a VO_2max test in a thermoneutral environment followed by two cycling ramp test trials, one in a temperate environment (18.3°C) and another in a hot environment (36.3°C). The ramp test consisted of 3-min stages of increasing intensity (+10% of VO_2max) while gas exchange, heart rate and perceived exertion were measured.

Results: During exercise, there was a main effect of the environment temperature on fat oxidation rate (F = 9.35, P = 0.014). The rate of fat oxidation was lower in the heat at 30% VO_2max (0.42 ± 0.15 vs.0.37 ± 0.13 g/min; P = 0.042), 60% VO_2max (0.37 ± 0.27 vs.0.23 ± 0.23 g/min; P = 0.018) and 70% VO_2max (0.22 ± 0.26 vs.0.12 ± 0.26 g/min; P = 0.007). In addition, there was a tendency for a lower maximal fat oxidation rate in the heat (0.55 ± 0.2 vs.0.48 ± 0.2 g/min; P = 0.052) and it occurred at a lower exercise intensity (44 ± 14 vs.38% ± 8% VO_2max; P = 0.004). The total amount of fat oxidised was lower in the heat (5.8 ± 2.6 vs 4.6 ± 2.8 g; P = 0.002). The ambient temperature also produced main effects on heart rate (F = 15.18, P = 0.005) and tympanic temperature (F = 25.23, P = 0.001) with no effect on energy expenditure (F = 0.01, P = 0.945).

Conclusion: A hot environment notably reduced fat oxidation rates during a ramp exercise test. Exercising in the heat should not be recommended for those individuals seeking to increase fat oxidation during exercise.

Keywords:

• Adiposity
• indirect calorimetry
• body temperature
• substrate oxidation
• body fat loss

Acknowledgments

The authors wish to thank the participants for their invaluable contribution to the study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Conflict of interest

The authors of this study have not received any support from any organisations for the submitted work. They do not have any financial relationships with any organisations that might have had an interest in the submitted work in the last three years. Lastly, the authors have not been involved in any relationships or activities that could seem to have influenced the submitted work.

Financial disclosure

This investigation did not receive any funding.

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.