Effects of reduced ambient temperature on fat utilization during submaximal exercise.
OBJECTIVE
The influence of cold air exposure on fuel utilization during prolonged cycle exercise was investigated.


METHODS
Nine male subjects cycled for 90 min in ambient temperatures of -10 degrees C, 0 degrees C, 10 degrees C, and 20 degrees C. External work performed between conditions was constant. Mean oxygen consumption (VO2) over the 90 min in the 20 degrees C trial corresponded to 64 +/- 5.8% VO2peak.


RESULTS
Although mean skin temperature was different between trials (P < 0.05), rectal temperatures were not different. At -10 degrees C and 0 degrees C, the respiratory exchange ratio was higher compared with 10 degrees C and 20 degrees 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 degrees C and 0 degrees C compared with 10 degrees C and 20 degrees 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 degrees C and 0 degrees C compared with 20 degrees 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 degrees C, 0 degrees C, and 20 degrees C trials, respectively. Mean VO2 was lower in the -10 degrees C trial than the 20 degrees C trial (2.53 +/- 0.06 vs 2.77 +/- 0.09. L.min-1; P < 0.05). Mean blood glucose concentrations were lower at -10 degrees C than 20 degrees 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 degrees C trial compared with all other trials (P < 0.05), plasma norepinephrine did not differ between trials.


CONCLUSIONS
The 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.
Layden
Joseph D
JD
Strathclyde Institute for Biomedical Sciences, University of Strathclyde, Glasgow, UK. j.layden@ucc.ac.uk
Patterson
Mark J
MJ
Nimmo
Myra A
MA
D000273:Adipose Tissue / Q000378:metabolism*; D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D000704:Analysis of Variance; D001642:Bicycling; D001831:Body Temperature; D003081:Cold Climate; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006339:Heart Rate; D006801:Humans; D050356:Lipid Metabolism; D008055:Lipids / Q000097:blood; D008297:Male; D011659:Pulmonary Gas Exchange; D013997:Time Factors
D005230:Fatty Acids, Nonesterified; D008055:Lipids