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

impacts aerobic performance [1–4]. The literature has shown the relevance of cooling strate- gies prior to exercise (pre-cooling) to limit the negative impact on aerobic performance [5–8]. Among these countermeasures, external (e.g., cooling vest, water immersion) and internal (e.g., drinking cold water/ice-slurry solution) cooling strategies mainly restrict the rise in body temperature and thereby increase the time to exhaustion [5, 8–11]. Wearing a cooling vest before exercise helps limit the core temperature increase [7, 8, 12, 13] and improves the rating of perceived exertion (RPE) and thermal perceptions [13, 14]–which, as behavioral controllers [15] can lead to a decrease in performance through an anticipatory and voluntary down-regu- lation of effort [16], thereby improving performance [6, 8, 12]. Pre-cooling ingestion strategies have shown beneficial effects on endurance capacity and performance [9, 17, 18], dependent on the temperature of the ingested solution [9, 18–21]. In addition, recent studies were focused on menthol, a compound of plant origin (Mentha), which acts on the TRPM8, TRPA1, and TRPV3 thermoreceptors [22], hence modifying inner and cutaneous thermal perceptions. A low dose of menthol used would activate the TRPM8 receptor which is usually activated by temperatures below 25˚C [22]. For example, a cooling sensation similar to the action of spray- ing cold-water on the face is provoked when menthol is applied to skin and mucosal surfaces [23]. In sport performance, several studies have clearly revealed the potentiating effect of men-

thol on cold solutions when they are ingested [18, 19, 24, 25] or applied [18, 26, 27]. Among these strategies, the ingestion of cold water or ice-slush with a menthol aroma was proven to be the most effective beverage for endurance exercise in a tropical climate: the colder the drink, the greater the effects [19]. According to a recent review on the ergogenic effects of pre-cooling in highly trained ath- letes [28], the best option for enhancing the benefits of pre-cooling strategies is to mix external and internal cooling. Indeed, it has been shown that the cumulative effect of two pre-cooling strategies enhances the cooling efficacy [7, 29, 30], and a combination of pre-cooling and water ingestion led to an increase in exercise endurance in a hot and humid environment [31]: the combination of cooling strategies enhanced heat storage capacity and decreased the cardio- vascular and thermoregulatory strains. Nevertheless, it should be noted that the pre-cooling method used in this study consisted in an immersion in a 25˚C water for 30 min. Although immersion, leading to a large and rapid reduction of core body temperature [32], seems to be the most effective pre-cooling strategy [5, 10, 18], it is time-consuming and logistically very difficult to use in real sports contexts [2, 33]. To overcome this issue, cooling vests, when suffi- ciently in contact with the skin (i.e., with numerous thermoreceptors) gave similar results [32]. Recently, a study concluded that the ice vests seem to be the most adopted pre-cooling strategy

by elite athletes but also the only one minimizing core temperature during the warm-up [34]: pre-cooling with a cooling vest for 20 min at rest before exercising increased endurance perfor- mance more than a 20-min warm-up [12], but athletes need to warm up, and scheduling a time for immersion beforehand lengthens their preparation and is not always practicable. Some experimentations tried to circumvent this problem by associating the cooling strategies with the warm-up, showing that warming up with a cooling vest limits the increase in core temperature [13, 14] and the thermal discomfort [13, 14], and improves aerobic performance [14]. Given the potentiating effect of menthol [18] and the ergogenic effect of mixed pre-cooling strategies [28] on aerobic performance, the main objective of this study was to investigate the added effect of mixed techniques (a combination of internal and external strategies, with and without menthol) during the warm-up on the aerobic performance (i.e., a 20-min cycling per- formance described as a time trial) in a tropical climate. The aim was to determine, in the trop- ical climate, (1) whether combined internal pre-cooling with menthol and external pre- cooling with or without menthol during a warm-up would improve cycling performance, PLOS ONE Tropical cycling performance and cumulative pre-cooling PLOS ONE | https://doi.org/10.1371/journal.pone.0291951 October 12, 2023 2 / 15