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

thermosensitivity [40], and, despite constituting only a small portion of the total skin surface area, dominate whole-body temperature perception [41]. These suggest that, in order to improve subsequent performance in the heat when a demanding warm-up is performed, future active investigations should focus on the head and/or the neck with a particular atten- tion to perceptions of the thermal environment (in addition of the core body temperature). Regarding menthol, it was expected that the addition of this compound of Mentha to the external pre-cooling in the mixed conditions (ICE-VEST and MEN-VEST) would improve the cycling performance, perceptions and cooling rate. As this study failed to show differences between the mixed conditions for these parameters during either the warm-up or the perfor- mance, it seems that the addition of menthol in skin precooling does not optimize the com- bined technique used here, i.e. internal pre-cooling with menthol and external pre-cooling. A study, with two independent variables (i.e., (1) with or without menthol, and (2) ambient or cold temperature), focused on the effects of a torso application of a 4% menthol solution dur- ing a running performance (i.e., 10 km) in tropical climate [42]. Compared to the control con- dition (water at ambient temperature), run performances were all improved but no differences were observed between the three experimental conditions either in performance or tempera- ture. Although our study focuses on precooling, but given the requirement of the warm-up (in

intensity and duration), our results confirms the fact that combining traditional external cool- ing with menthol do not add value for a performance in hot and humid conditions. Another explanation would be that the ingestion of the cold menthol water in both mixed conditions could have a stronger impact than that of the cooling vest, not allowing sufficiently discrimi- nate the potential effects of cutaneous application (cold water and menthol+cold water) by wearing the vest. Further data are needed to (1) to isolate the effect of ingestion (internal cool- ing) from that of application to the skin (external cooling) and thus, determine whether an internal pre-cooling with menthol is sufficient alone for short distance time trials (e.g., by comparing with no pre-cooling and/or internal pre-cooling without menthol), and (2) investi- gate the add-value of the menthol on skin external application during an active warm-up in hot and humid conditions. Several studies have suggested an effect of the duration of the pre-cooling and/or the dura- tion of the rest interval [18, 21, 43, 44]. For example, a longer pre-cooling period (i.e., >30 min) would be beneficial for subsequent performance [43, 44] and a better pre-cooling effect on performance was observed with cold menthol beverage drunk over 1 hour instead of 30 min [18]. Naito et al. showed that a long rest interval (i.e., 20 min rest versus 5 min rest) after internal pre-cooling by ice ingestion had the greatest positive effect on exercise capacity

(cycling performance time to exhaustion) in a hot and humid environment [21]. In our study, the transition between the end of the 30-min warm-up and the beginning of the cycling perfor- mance was 5 min. Despite the combination of two cooling strategies (internal and external), the transition time after a very active warm-up (reflected by the continuous increase of the RPE from T5 to T25 before a decrease at the end of the warm-up) was probably not long enough to allow the cyclists to benefit from the effects of the different pre-cooling strategies that are supposed to limit the heat storage capacity and the increase in the thermal perception. Although no condition differences were found during either the warm-up or the cycling performance, an increase of the thermal sensation was observed during the cycling perfor- mance only in the NO-VEST condition, without any modification of the comfort. At the end of the performance, the participants seem to have perceived the environment as being warmer in the condition in which they did not wear the cooling vest during the warm-up. Compared to the “static” warm-up, achieving a cycling performance in an ecological situation (e.g., a velo- drome) has the advantage of benefiting from the movement of air allowing an optimization of the convection process, thus enabling evaporative thermolysis capabilities [45]. The absence of PLOS ONE Tropical cycling performance and cumulative pre-cooling PLOS ONE | https://doi.org/10.1371/journal.pone.0291951 October 12, 2023 10 / 15