Deception of pre-heating and body core temperature improves self-paced 3K running of females in hot, humid conditions

Marino et al (2004: Comparative Biochemistry and Physiology - Part B: Biochemistry & Molecular Biology, 139, 561–569) has proposed that exercise in the heat can result in the self-selection of lower exercise intensities (i.e. pacing), to reduce the rate of rise in core temperature and avoid a premature cessation of exercise. Accordingly, it is unclear whether just the perception of higher or lower temperatures can alter pacing strategies during exercise. The purpose of this study was to investigate whether providing incorrect information of the preheating and core temperature would alter self-paced, 3K running in the heat. Ten physically active females ran three, 3K time trials in the heat (temperature mean 30.9, s = 1.0ºC; relative humidity mean 54.1, s = 4.7%) in a randomized order during the follicular phase of their menstrual cycle. Prior to each time trial, participants were pre-heated for 20 min by water immersion in temperatures they believed to be 34ºC, 37ºC and 40ºC (actual temperature in all conditions was mean 37.0, s = 0.5ºC). During the 34ºC trial participants received visual feedback that their core temperature was 0.3oC lower than it actually was, and in the 40ºC trial, 0.3ºC higher than it actually was. Before and after the time trial voluntary force (maximal voluntary contraction (MVC), peak twitch force (Pf) and voluntary activation (VA) using superimposed electrical stimulation were examined in the right knee extensors during repeated (10 x 5 s) isometric contractions in temperate conditions. Measures of core temperature, heart rate, ratings of perceived exertion (RPE) and thermal sensation (TS) were recorded at 1K intervals during the time trial. Institutional ethics approval was granted for this investigation. Running times were faster in the 34oC trial compared with the 40oC trial at 1K (5.1%, P = 0.04), 2K (4.0%, P = 0.02) and 3K (4.6%, P = 0.02). No differences existed in performance times during the 37oC trial compared to either the 34oC or 40oC trial for any distance. No differences were found for MVC, Pf and VA within, or between conditions. Core temperature, heart rate, RPE and TS increased significantly during the 3K time trial in each condition (P < 0.05), but no differences were found between conditions. Deception of preheating treatment and core temperature using a lower temperature improved 3K running performance compared to when a higher temperature deception was used. This occurred without differences in physiological measures, or contractile function and supports previous evidence that a pacing strategy can be manipulated; in this study by incorrect perception of temperature. Correct knowledge of internal and external temperature could be important for athletes, otherwise they may underperform if they perceive a greater heat load to exist.