Effects of pre-exercise sucrose ingestion on thermoregulatory responses to near-maximal 5-km running

Research has shown that carbohydrate consumption can increase body temperature at rest and, in some cases, during exercise. Most exercise studies, however, haven't matched exercise intensity between carbohydrate and placebo conditions. The purpose of this randomized, double-blind, placebo-controlled trial was to examine whether pre-exercise carbohydrate consumption independently accelerates the usual temperature rise with intense exercise. Twenty-eight runners self-reported 5-km performance (16-23 min) and were randomized, using a matched-pairs design, to 750 ml water containing 100 g sucrose or 0.8 g aspartame. Beverages were consumed 60 min before running at 93% of maximum 5-km speed in temperate conditions. Gastrointestinal temperature, Thermal Sensation Scale (TSS) and Feeling Scale (FS) were recorded before ingestion, every 10 min during 60 min of rest, and every 1-km during the 5-km run. Rating of Perceived Exertion was recorded every 1-km. Independent samples t-tests and two-way mixed ANOVAs with repeated measures assessed whether there were baseline differences or treatment effects. Gastrointestinal temperature didn't differ between carbohydrate (38.7 ± 0.4 °C) and placebo (38.6 ± 0.4 °C) by the end of the 5-km (p = 0.49). No group x time interactions or main group effects were found, except for a modest interaction for TSS (F = 2.1, p = 0.02, partial η2 = 0.075). Time effects were found for all outcomes, with temperature, TSS, and RPE increasing, and FS decreasing, during the run. Ingesting 100 g of sucrose prior to intense running lasting < 25 min didn't influence gastrointestinal temperature and therefore doesn't likely impact on the risk of heat illness.