Effects of Heat Acclimation on Time Perception

AbstractPhysical and mental performance is impaired during prolonged exercise in hot environments (Gonzalez-Alonso et al., 1999) compared to thermoneutral conditions. These effects are related to changes in body temperature and alterations in the central nervous system functioning (CNS; Nybo & Nielsen, 2001). Repeated exposure to exercise-related heat stress results in physiological adaptations that, in turn, lead to performance improvements (Burk et al., 2012; Wendt et al., 2007). Exploring temporal processing with temperature manipulations suggests the existence of a temperature sensitive time mechanism that is mediated through the level of arousal (Wearden & Penton-Voak, 1995). However, we recently demonstrated that in addition to physiological factors like core temperature, psychological response to heat stress should be considered as well (Tamm et al., 2013).Healthy young male participants took part in two slightly different acclimation programs (i.e., daily moderate exercise at similar ambient temperature). The first group (N=20) followed a 10-day program with gradual increase in exercise intensity (first half of the program at 55% of individual VO2max and second half at 60% of individual VO2max) with two 50-min exercise periods on a treadmill, separated with a 10-min rest period. The second group (N=20) participated in an 8-day acclimation program where they exercised at varying intensity level to keep the core temperature at a fixed level of 38.5-39°C. The exercise trial consisted of three 30-min periods of exercise separated with two 5-min rest periods. Before (H1) and after (H2) the acclimation programs, both groups performed acute exercise trial until exhaustion at 42°C with the humidity level at 18%. In the control condition, participants exercised in a thermoneutral environment (22°C), duration equal to H1 trial. Several state indicators like core temperature (T) and heart rate (HR), ratings of perceived fatigue and exertion (CR-10 & RPE, respectively; Borg, 1998), critical flicker frequency (CFF) were obtained for estimating both physiological and psychological perspectives on status change. In addition, participants performed cognitive testing measuring performance in short-term and working memory tasks under stressful conditions. Blood samples for estimating changes in hormone measures were included. Previous results indicate the response of blood prolactin (PRL) to exercise in the heat is related to endurance capacity and the rate of increase of PRL concentration is reduced after heat acclimation (Burk et al., 2012). Acclimation effects on cognitive performance, including time perception, are seldom if ever explored. The current study investigates time production during acute exercise in the hot environment before and after heat acclimation program. More precisely, we are interested in the physiological and psychological factors that contribute to the temporal performance under stressful conditions and what are the characteristics of adaptation to such conditions.A time production task was administered before, after 10 and 60min of exercise, and after ending the trial. Heart rate, temperature, and subjective state measures were obtained during the exercise with a 10-min interval. Blood samples were collected before, during (at 60min) and after the exercise trial. Linear function was used for analyzing the relationship between subjective time and real time in a time production task. If regression coefficient is sufficiently close (a1=1) then produced time intervals are identical to time intervals indicated by the task. The results showed that for both groups, significant temporal compression occurred (a1