NICOSIA, Cyprus—Fatigue attributed to exercising in relatively cold temperatures can be primarily attributed to a loss of glycogen, not any type of neurological effects, according to a new study (J Intl Soc Sports Nutr. 2010;7:22. DOI:10.1186/1550-2783-7-22). Researchers from the University of Nicosia and University of Glasgow, Scotland, recruited 10 trained cyclists to perform three constant-load cycling tests at 73 percent VO2max to exhaustion at 10 degrees Celsius. Prior to the tests, the subjects consumed a control diet, 90 percent fat meal with caffeine, and 90 percent fat meal without caffeine.

Time to exhaustion was not different between the test fat meals, regardless of caffeine intake; there were also no differences in brain serotonergic or dopaminergic function. However, caffeine did appear to reduce leg muscular discomfort, and also increased the ratio of plasma free-tryptophan to large neutral amino acids. The researchers concluded the brain's 5-HT and dopaminergic systems do not appear to impact the fatigue process, suggesting fatigue when exercising in cold temperatures primarily is attributed to glycogen depletion.

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