Athlete perceptions of flavored, menthol-enhanced energy gels ingested prior to endurance exercise in the heat

Background L-menthol evokes a cooling sensation by activating cold sensing cation channels. Menthol-enhanced fluids can be ergogenic during exercise in the heat by improving thermal perception; hence, the addition of menthol to energy gels may benefit athletes. Previously, unflavored menthol gels were deemed acceptable at 0.1% concentration, but no research has been undertaken on menthol gels with additional flavoring. Therefore, we determined athlete perceptions of flavored energy gels with different menthol concentrations. Methods With a randomized, crossover, double-blind, placebo-controlled design, 27 athletes (34.8 +/- 6.7 y, 9 females) ingested an energy gel with either 0.1%, 0.3%, 0.5%, or 0.7% menthol concentration, or a non-menthol, flavor-matched placebo (CON), on separate occasions before outdoor exercise. Gels were rated for cooling sensation, irritation, flavor, and overall experience on 100-point sensory and hedonic labeled magnitude scales. The duration of any cooling sensation was also reported. Results All menthol gels delivered a greater cooling sensation compared to CON (7.4 +/- 8.1 AU) with a significantly greater response for 0.7% (59.9 +/- 20.5 AU) and 0.5% (57.7 +/- 21.8 AU), compared to all others. Irritation was higher for all menthol gels compared to CON (3.4 +/- 7.2 AU) and for 0.7% compared to 0.1% (31.1 +/- 31.0 vs. 16.3 +/- 21.0 AU, p = 0.041), with none rated above a 'mild-moderate' intensity. The menthol gels delivered a significantly longer cooling sensation duration (12.3-19.6 min) versus CON (2.2 +/- 4.8 min) with no difference between menthol gels. Conclusion A flavored menthol energy gel at 0.1-0.7% concentration provides a cooling sensation for athletes when ingested before exercise. The 0.5% concentration is recommended to maximize the cooling sensation whilst minimizing irritation.