Exogenous Glucose Supplementation Blunts Declines In Cognitive Processing Speed Due To Prolonged Exercise In The Heat.

PURPOSE: To determine if electrolyte or carbohydrate supplementation vs. plain water would limit the magnitude of dehydration and decline in cognitive function in humans. METHODS: 24 subjects performed 3 visits consisting of 2hrs of walking at 3mph/7% grade in an environmental chamber set to 33ºC/10% RH. In random order, subjects consumed water (W), water+electrolyte (GZ), or water+electrolyte+sugar (G). Throughout exercise (EX), subjects carried a 23kg pack, and drank ad libitum. Pre and post EX, body mass (BM) and plasma osmolality (pOsm) were measured. Physiological Strain Index (PSI), an index of cardiovascular and thermal stress, and core temperature (TC) were recorded every 15mins. Plasma glucose (GLU) was measured every 30mins. Cognitive processing speed, measured via the Stroop Test (SCWT), was measured post EX and compared to baseline (BL). A subset of 8 subjects performed a normothermic (N) protocol (21ºC/ambient humidity) to ascertain how the exercise stimulus would influence hydration status and cognitive function in the absence of heat. RESULTS: There were no significant differences between fluid conditions (W, GZ, & G) for BM loss (Δ3.2±0.2, 3.1±0.2, & 3.0±0.3kg), fluid consumption (1.9±0.2, 1.9±0.2, & 1.8±0.2L), pOsm (Δ1.5±2.7, 2.2±2.4, & 2.0±1.5mmol/L), peak PSI (7.5±0.4, 7.0±0.6, & 7.9±0.5), and peak TC (38.7±0.1, 38.6±0.1, & 38.8±0.2ºC). Compared to W and GZ, GLU significantly increased from BL in the G condition (107±4 & 109±3mg/dL at 90 & 120mins, P<0.05). Compared to BL values, SCWT performance significantly decreased in all conditions (463±93, 422±83, & 140±52ms for W, GZ, & G, P<0.05). Importantly, compared to the W and GZ conditions, the SCWT performance was significantly attenuated in the G condition (P<0.05). As expected, when compared to the heat stress protocol (W, GZ, & G), the N condition resulted in lower BM loss, fluid consumption, and peak PSI (2.0±0.1kg, 1.2±0.7L, & 4.8, respectively). CONCLUSIONS: These data are the first to suggest that, independent of supplementation variety, cognitive processing significantly decreases immediately following long duration exercise in the heat in healthy humans. Compared to water and fluids supplemented with only electrolytes, fluids supplemented with carbohydrates significantly blunts this decrease in cognitive function. [ABSTRACT FROM AUTHOR]