Author(s): NAITO, T., SAITO, S., MORINAGA, H., TAKAI, Y., AKAZAWA, N., Institution: HOKKAI-GAKUEN UNIVERSITY, Country: JAPAN, Abstract-ID: 888

INTRODUCTION:
The combination of mental fatigue resulting from a prolonged cognitive task and exposure to heat stress has been demonstrated to result in impaired exercise capacity in the heat. Body cooling before and during exercise under combined heat stress and mental fatigue reduced heat strain and improved subsequent aerobic exercise capacity compared with no-cooling. In this previous study, reductions in core temperature and skin temperature improved aerobic exercise capacity. However, under heat stress alone, even an increase in skin temperature alone has been shown to impair exercise capacity. Therefore, under combined heat and mental stress, reducing skin temperature may mitigate this stress and suppress declines in exercise capacity. The purpose of this study was to investigate the effects of cooling skin surface during exercise with mental fatigue on aerobic exercise capacity in the heat.
METHODS:
Eight non-heat-acclimatized recreational male athletes (age: 22 ± 1 years, height: 172.8 ± 6.7 cm, body mass: 67.56 ± 6.19 kg, maximal oxygen uptake [VO2max]: 49.9 ± 5.2 mL/kg/min) performed two trials: hot condition (35°C, HOT), and hot condition (35°C) with cooling intervention (COOL). Participants were conducted AX-Continuous Performance Task (AX-CPT) during the 45-min 50%VO2max cycling exercise under each condition. After rest for 5 min, participants performed the cycling exercise at an intensity equivalent to 75%VO2max until reaching voluntary exhaustion. Cooling intervention was conducted during exercise used wearing water-perfused suits with water at 1℃.
RESULTS:
All participants had the shortest time for the HOT trial. Time to exhaustion was significantly longer in the COOL trial (377.3 ± 133.7 sec; Effect size (ES) = 1.31; p < 0.05) than in the HOT trial (238.4 ± 74.8 sec). There were no significant differences in rectal temperature, localized sweating on the forearm, and heart rate between the HOT and COOL trials throughout the experiment (p > 0.05). The mean skin temperature was lower in the COOL trial than in the HOT trial during the 45-min 50%VO2max cycling exercise (p < 0.05). Thermal sensation was significantly lower in the COOL trial than in the HOT trial (p < 0.05), albeit no significant differences in thermal discomfort and rating of perceived exertion. Self-reported mental fatigue using visual analog scale was significantly higher after tasks in each trial (p < 0.001), but no significantly differences between trials (HOT: 8.0 ± 1.0, COOL: 7.2 ± 1.6 p > 0.05).
CONCLUSION:
The results of this study showed that the skin surface cooling during exercise under combined heat stress and mental fatigue improved subsequent aerobic exercise capacity compared with no-cooling. This observation suggested that athletes who exercises with mental fatigue in the heat should be cooling their skin surface, even when core temperature cannot be cooled.