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Purpose: Open-water swimmers need to train with wetsuits to get familiar with them; however, body core temperature (Tcore) kinetics when using wetsuits in swimming-pool training remains unclear. The present study assessed the effects of wetsuit use in pool training on Tcore, subjective perceptions, and swimming performance to obtain suggestions for wearing wetsuits in training situations., Methods: Four elite/international-level Japanese swimmers (2 female, age 24 [1] y) completed two 10-km trials with (WS) and without wetsuit (SS) in the swimming pool (Tw: 29.0 °C). During the trial, swimmers were allowed to remove their wetsuit if they could no longer tolerate the heat. Tcore was continuously recorded via ingestible temperature sensors. Swimming speed was estimated from every 100-m lap time., Results: Tcore increased by distance in both trials in all swimmers. Tcore when swimmers removed their wetsuit in the WS (distance: 3800 [245] m, time: 2744 [247] s) was higher than that at the same distance in the SS in all swimmers. Rating of perceived exertion was higher in the SS than the WS, and swimming speed was slower in the WS than the SS in all swimmers., Conclusion: Wetsuit use during pool training increases Tcore and decreases swimming performance. Although wearing wetsuits in training situations is important for familiarization, for the safety of the swimmers, it is recommended that they remove their wetsuit if they feel too hot.

Purpose: To assess the core temperature fluctuations during 10-km open-water swimming (OWS) in cool water and the relationship between thermal sensation (TS) after 10-km OWS, core temperature, and local skin thermal sensitivity. Methods: Nine highly trained OWS swimmers (4 female; age 22 [3] y) completed a single 10-km trial in cool water (22.3 °C) wearing swimsuits for OWS. During the trial, core temperature was continuously recorded via ingestible temperature sensors, and TS after trial was also measured. Then, local skin warm/cool sensitivity was measured in the forearm. Results: All swimmers completed the 10-km OWS. Mean swimming speed for males and females were 1.39 (1.37–1.42 m/s) and 1.33 m/s (1.29–1.38 m/s), respectively. Core temperature increased in 8 out of 9 swimmers during 10-km OWS (P =.047), with an average increase of 0.8 °C. TS after 10-km OWS varied among swimmers. There were no correlations between post-OWS TS and post-OWS core temperature (P =.9333), whereas there was a negative correlation between post-OWS TS and local skin cool sensitivity (P =.0056). Conclusion: These results suggest that core temperature in elite swimmers might not decrease during 10-km OWS in the cool water temperature of official OWS. In addition, individual differences in TS after 10-km OWS may be related to skin cool sensitivity rather than core temperature. [ABSTRACT FROM AUTHOR]

Introduction: Caffeine is an exercise performance enhancer widely used by individuals engaged in training or competition under heat-stressed conditions. Caffeine ingestion during exercise in the heat is believed to be safe because it does not greatly affect body temperature responses, heart rate, or body fluid status. However, it remains unknown whether caffeine affects hyperthermia-induced hyperventilation or reductions in the cerebral blood flow index. We tested the hypothesis that under conditions inducing severe hyperthermia, caffeine exacerbates hyperthermia-induced hyperventilation and reduces the cerebral blood flow index during exercise. Methods: Using a randomized, single-blind, crossover design, 12 physically active healthy young men (23 ± 2 yr) consumed a moderate dose of caffeine (5 mg·kg−1) or placebo in the heat (37°C). Approximately 60 min after the ingestion, they cycled for ~45 min at a workload equal to ~55% of their predetermined peak oxygen uptake (moderate intensity) until their core temperature increased to 2.0°C above its preexercise baseline level. Results: In both trials, ventilation increased and the cerebral blood flow index assessed by middle cerebral artery mean blood velocity decreased as core temperature rose during exercise (P < 0.05), indicating that hyperthermia-induced hyperventilation and lowering of the cerebral blood flow occurred. When core temperature was elevated by 1.5°C or more (P < 0.05), ventilation was higher and the cerebral blood flow was lower throughout the caffeine trial than the placebo trial (P < 0.05). Conclusions: A moderate dose of caffeine exacerbates hyperthermia-induced hyperventilation and reductions in the cerebral blood flow index during exercise in the heat with severe hyperthermia. [ABSTRACT FROM AUTHOR]

• Whole-body thermal sensation score declined as core temperature decreased. • Whole-body thermal sensation of hypothermia was blunted by exercise compared to rest. • Local skin thermal sensation did not differ between rest and exercise. Thermal sensation, a key component of behavioral thermoregulation, is modulated by the changes in both skin and core temperatures. Although cutaneous thermal sensation to local cold is blunted during exercise as compared to rest in normothermic humans, it remains to be determined whether this holds true during core cooling. Furthermore, when local skin thermal sensation is diminished during exercise, it remains unclear whether whole-body thermal sensation is also attenuated. We therefore tested whether low-intensity exercise (VO 2 : ~1300 ml min−1) attenuates local skin and/or whole-body thermal sensation in hypothermic young males. Eleven healthy young males (24 ± 2 years) were cooled through cold water immersion (18 °C) up to their lower abdomen while resting (rest trial) and during low-intensity cycling (30–60 W, 30 rpm) (exercise trial). Body temperature, cardiorespiratory variables, and whole-body (9-point scale: 0, unbearably cold; 4, neutral; 8, unbearably hot) and local skin thermal sensation were measured at baseline on land and before the esophageal temperature (T es) began to decrease (defined as -0.0 T es) and after 0.5 and 1.0 °C decrements in T es from baseline during the immersion period. Local skin thermal sensation was measured using a thermostimulator with Peltier element that was attached to the chest. The temperature of the probe was initially equilibrated to the chest skin temperature, then gradually decreased at a constant rate (0.1 °C s -1) until the participants felt coolness. The difference between the initial skin temperature and the local skin temperature that felt cool was assessed as an index of local skin thermal sensation. Throughout the immersions, esophageal and mean skin temperatures did not differ between the rest and exercise trials. Local skin thermal sensation also did not differ between the two trials or at any core temperature level. By contrast, the whole-body thermal sensation score was higher (participants felt less cold) in the exercise than in the rest trial at esophageal temperature of -1.0 °C (1.25 ± 0.46 vs. 0.63 ± 0.35 units, P = 0.035). These results suggest that local skin thermal sensation during low-intensity exercise is not affected by a decrease in core temperature. However, whole-body thermal sensation mediated by a decrease in core temperature (-1.0 °C) is blunted by low-intensity exercise during cold water immersion. [ABSTRACT FROM AUTHOR]