Cumulative pre-cooling methods do not enhance cycling performance in tropical climate

an increase in the thermal sensation at the end of the cycling test under conditions where the subjects wore a cooling vest during warm-up, with or without menthol, suggests a beneficial effect of wearing a cooling vest on thermal perception although it had no effect on perfor- mance: the thermal sensation may have engaged the athlete to maintain a greater intensity of exercise and for longer leading to, visually on Fig 1, a homogeneous and constant effort over time as discussed previously. Given all these, it could be that the final cycling task of 20 min was not long enough to identify the possible benefits of wearing a cooling vest in the mixed conditions. Indeed, a study on a 2000-m rowing female performance showed no improvement in performance after a (passive) pre-cooling period, probably due to the short exercise time [46]. Rodriguez et al. concluded in their review that better results from the application of pre- cooling were observed in prolonged physical exercise than in short bouts [28]. In 2002, Marino also questioned the benefit of pre-cooling strategies for short-duration exercises and empha- sized the likely effectiveness for endurance exercise of up to 30–40 minutes [47]. In our study, the exercise was probably not long enough to observe an effect of pre-cooling on performance. Finally, the thermal sensation analyses revealed a continuous increase over time in all con- ditions before the decrease at the end of the warm-up without affecting the thermal comfort. These results are probably due to the metabolic heat production generated by the exercising

muscles during the warm-up without condition difference. Although caution is needed given the small sample size, the lack of condition differences during the warm-up and the cycling performance could suggest that the mixed interventions may not have been discriminating enough to limit the increase in the perception of exertion during the warm-up and to positively impact the cycling performance, the latter being proba- bly too short. Regarding the period, the analyses showed a continuous increase over time in all conditions before the decrease at the end of the warm-up. These results confirmed that the participants correctly performed the warm-up, finding it increasingly more difficult as the imposed inten- sity increased from T0 to T25. The HR analyses showed a clear increase over time during the warm-up and performance in all conditions, attesting to the exercise-induced increase in cardiac load. Although an inter- action effect was observed during the warm-up, suggesting pattern differences between the conditions, caution is needed due to the small sample size, especially that no effect of menthol has been shown on heart rate during sport performance [48]. Regarding the cooling rate, no difference between conditions was found for ΔTgi during warm-up or the cycling perfor- mance. Despite a large interindividual variation and a small sample, it is interesting to visually note on the Fig 2 temperature differences between conditions. During the warm-up (Fig 2A), the temperature difference was greater in NO-VEST condition, assuming a greater increase in

temperature without a cooling vest, whereas the differential was not very emphasized in the mixed conditions with a vest. Conversely, it should be noted that the temperature difference during the performance appeared to be greater in the mixed conditions (i.e., conditions with cooling vests during the warm-up). Although caution is needed with these data, the athletes, due to the cooling vests worn during the warm-up, could have benefited from a greater ampli- tude of temperature change leading them to maintain a better consistent performance (as pre- viously discussed with the Fig 1). A study on the thermoregulatory influence of a cooling vest concluded that this interven- tion did not rapidly reduce elevated body temperature and did not improve the cooling rate [49]. In our study, the cooling vest (external pre-cooling with or without menthol) was associ- ated with the ingestion of cold menthol water (internal pre-cooling) during the warm-up in two out of the three conditions (ICE-VEST and MEN-VEST). As the third condition was only an internal pre-cooling with ingestion of cold menthol water during the warm-up, our results PLOS ONE Tropical cycling performance and cumulative pre-cooling PLOS ONE | https://doi.org/10.1371/journal.pone.0291951 October 12, 2023 11 / 15