Thermal perception during exhaustive exercise in thermally stressful conditions

Thesis (M.S., Kinesiology (Exercise Science))--California State University, Sacramento, 2012.The mechanisms of caffeine and other adenosine antagonistic pharmaceuticals are theorized to act primary at the central level. Previous research has shown that depression of rate of perceived exertion (RPE) during exercise has been depressed following caffeine (Caff) consumption. An unchanged perception of thermal score (TS) despite increased core temperature (Tc) has also been shown. Athletes may be prone to heat illness if TS and RPE perception is decreased during exercise in thermally challenging environments. Purpose: To determine the influences of caffeine on perceptual variables and time to exhaustion during continuous, sub-maximal exercise in a heated chamber, using trained cyclists. Methods: Nine competitive cyclists completed a graded exercise test (GXT) and a sub-maximal detection test, identifying VO2peak and the power [watts (W)] at 5% below the first ventilation threshold (VT1), respectively. One control (C) trial was conducted, followed by two double-blind trials using caffeine (5mg/kg bodyweight) or a placebo. All trials were held at constant load exercise at the W reported from the sub-maximal test, and were conducted to exhaustion or terminating criteria. All trails were held in a heated chamber to 35-37??C and 30-40% humidity. Analysis between the trials used a two-way repeating measures ANOVA, with an ??-level of .05. \ud There was no significant effect on time to exhaustion (TTE). End trial Tc for Caff trials was significantly different than placebo (P), p = .009. However, no difference was found for average mean Tc between trials. No significant difference was found for TS or RPE. Significant difference in Thirst (THS), p =.048, was found between P and C. Strong correlation \ud (r =.834, r =.832, r =.916) existed between time and Tc for C, P, and Caff, respectively. C, P, and Caff were highly correlated for Tc vs. TS, (r =.872, r =.754, r =.803), respectively. For RPE, C, P, and Caff were highly correlated, (r =.782, r =.717, r =.876), respectively. Slope-intercept analysis found Caff to have higher y-intercept for Tc, and depressed y-intercepts for RPE, TS, and THS when compared to P. The results of this investigation found perceptual variables and TTE to not be significantly affected by Caff, although trends towards significance were present. This investigation found the Caff group to have end-trial Tc that was significantly higher than P with no increase in TS or RPE. It may be possible that Caff promotes tolerance of higher Tc due to decreased perceptual feedback at the central level. It may also be possible that the instruments used to collect TS were not appropriate to detect significant difference in TS.Kinesiology (Exercise Science