Author(s): GILGEN-AMMANN, R., SCHWEIZER, T., Institution: SWISS FEDERAL INSTITUTE OF SPORT MAGGLINGEN, Country: SWITZERLAND, Abstract-ID: 2422

INTRODUCTION:
Environmental heat stress and physical activity (PA) interact synergistically to increase strain on physiological systems [1]. Heat acclimatization is an important precaution as it induces biological adjustments that reduce these negative effects of heat stress. The adaptations achieved through endurance training also have a major influence on thermotolerance [2]. But what about the individual perception of heat stress? We aimed to investigate whether the subjective perception of heat sensation and heat comfort differed according to fitness level with increasing core body temperature (CBT). .
METHODS:
16 healthy volunteers (7 female, 27 ±6 years, 174 ±9cm, 69 ±9kg) performed 6 activities for 8 minutes each: lying, walking, housekeeping, jogging, strength training, cycling and high intensity interval training (HIIT). Immediately after each activity, subjects reported perceived exertion (Borg scale, 6-20), heat sensation (very cold - very hot, 7-Likert scale) and heat comfort (pleasant - extremely pleasant, 5-Likert scale). The protocol was carried out under normal conditions (average 19.4°C) and again under hot conditions caused by wearing several layers of (nonpermeable) clothing. The group was divided into untrained subjects doing <150min of moderate PA (N=4), and trained subjects doing >150min of moderate PA per week. The rectal thermistor (MSR Electronics GmbH, Henggart, Switzerland) measured CBT and was self-inserted to a depth of 10cm beyond the anal sphincter.
RESULTS:
With increasing PA intensity and under hot conditions, CBT was significantly higher (average 36.9°C vs. 37.7°C, p=.009). The maximum CBT was 38.8°C in both groups and the average Borg values after HIIT activity were 19.0 and 18.8 for untrained and trained subjects, respectively. Subjective heat sensation (p=.002) and heat comfort (p=.003) were significantly higher with increasing CBT. There was neither a difference in CBT nor a difference in perceived heat sensation, heat comfort or heat sensation*comfort interaction depending on fitness level.
CONCLUSION:
Endurance training leads to adaptive changes to the physiological, immunological, and neuroendocrine systems [2]. However, there was no difference between untrained and trained subjects in terms of subjective heat sensation and heat comfort with increasing CBT. As our sample of untrained subjects was small and the ethical upper limit for CBT was not reached, further research is needed to understand differences in subjective heat perception.
References:
1. Sawka MN, et al. (2011). Integrated physiological mechanisms of exercise performance, adaptation, and maladaptation to heat stress. Compr Physiol 1, 1883–1928.
2. McLellan TM, et al. (2012). Influence of Aerobic Fitness on Thermoregulation During Exercise in the Heat. Exerc Sport Sci Rev 40(4), 218-219.