Effects of reduced ambient temperature on fat utilization during submaximal exercise


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Abstract

LAYDEN, J. D., M. J. PATTERSON, and M. A. NIMMO. Effects of reduced ambient temperature on fat utilization during submaximal exercise. Med. Sci. Sports Exerc., Vol. 34, No. 5, pp. 774–779, 2002.PurposeThe influence of cold air exposure on fuel utilization during prolonged cycle exercise was investigated.MethodsNine male subjects cycled for 90 min in ambient temperatures of −10°C, 0°C, 10°C, and 20°C. External work performed between conditions was constant. Mean oxygen consumption (O2) over the 90 min in the 20°C trial corresponded to 64 ± 5.8% O2peak.ResultsAlthough mean skin temperature was different between trials (P < 0.05), rectal temperatures were not different. At −10°C and 0°C, the respiratory exchange ratio was higher compared with 10°C and 20°C (0.98 ± 0.01 and 0.97 ± 0.01 vs 0.92 ± 0.01 and 0.91 ± 0.01;P < 0.05). The associated rates of fat oxidation were lower at −10°C and 0°C compared with 10°C and 20°C (0.15 ± 0.06 and 0.17 ± 0.06 vs 0.35 ± 0.06 and 0.40 ± 0.04 g·min−1;P < 0.05). Blood glycerol was lower at −10°C and 0°C compared with 20°C (P < 0.05); mean values were 0.13 ± 0.0, 0.13 ± 0.0, and 0.18 ± 0.0 mmol·L−1 for the −10°C, 0°C, and 20°C trials, respectively. Mean O2 was lower in the −10°C trial than the 20°C trial (2.53 ± 0.06 vs 2.77 ± 0.09. L·min1;P < 0.05). Mean blood glucose concentrations were lower at −10°C than 20°C (4.9 ± 0.2 vs 5.3 ± 0.1 mmol·L−1;P < 0.05). Although plasma epinephrine concentrations were greater during the 20°C trial compared with all other trials (P < 0.05), plasma norepinephrine did not differ between trials.ConclusionThe diminished fat oxidation at colder temperatures potentially reflects a reduction in lipolysis and/or mobilization of FFA or impairment in the oxidative capacity of the muscle.

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