REF-966 · Barwood et al., 2025 · International Journal of Sports Physiology and Performance, Vol. · Paper · PubMed

Perceptual, Thermoregulatory, and Performance Effects of Menthol Gel Application in Trained Triathletes Exercising in Hot Conditions

Blimited evidenceMeasured on trained to highly trained athletesWritten before October 2026, being re-checked

Topical menthol had been reported to cut sweat production in hot environments; the authors tested whether that would keep triathletes better hydrated through a warm-water swim and improve the cycling that follows.

Eight trained triathletes did two conditions, with whole-body menthol gel applied beforehand (40 g, 3.5% menthol) or no gel: a 30-minute swim in tropical (29 °C) water at 85% of their 400-m personal best, then a self-paced 20-km cycling time trial. Wet-bulb globe temperature was at "red flag" level.

Terminal gastrointestinal temperature was 38.8 °C in both conditions, time-trial performance did not differ (39:36 vs 40:53 minutes; P = .340), and the gel condition produced more sweat (1140 [257] mL vs 961 [202] mL; P = .042). The authors conclude that menthol improved perception, did not enhance performance and increased thermoregulatory sweating.

Participants

n=8 trained triathletes: 36 [5] y old, 1.77 [0.1] m tall, 73.9 [8.0] kg body mass. Sex is not given in the abstract.

Protocol

Two conditions: whole-body application of menthol GEL (40 g, 3.5% menthol) vs NO-GEL, applied before exercise.
Protocol: a 30-minute swim in tropical (29 °C) water at 85% of their 400-m personal best, then a self-paced 20-km cycling time trial.
Measures: sweat production; deep body temperature (gastrointestinal pill) and skin temperature; thermal sensation, thermal comfort and rating of perceived exertion.
Conditions reached "red flag" on wet-bulb globe temperature, meaning potential for heat injury in every participant.

Key Results

MeasureGELNO-GELStatistics
20-km time trial39:36 (04:31) min40:53 (05:53) minP = .340; 95% CI, -222 to 88 s; d = -0.22
Terminal gastrointestinal temperature38.8 °C (0.3 °C)38.8 °C (0.7 °C)—
Sweat production1140 [257] mL961 [202] mLP = .042; d = 0.77
Authors' conclusion: menthol improved perception, yet it raised thermoregulatory sweating and gave no performance benefit (partial hypothesis support).

Practical Application

In eight trained triathletes (crossover, gel vs no gel) a whole-body 3.5% menthol gel applied before a 30-minute swim in 29 °C water and a 20-km cycling time trial in "red flag" heat improved how they felt but did not make them faster (39:36 vs 40:53 minutes, P = .340), left terminal gastrointestinal temperature the same (38.8 °C in both conditions) and increased sweat production (1140 vs 961 mL, P = .042). To "will menthol gel help me through a hot swim and bike?": it changed the feeling, not the result, and it cost more sweat.
The direction of the sweat effect is the opposite of the earlier spray trial (REF-965, sweating reduced), so topical menthol does not have one consistent effect on sweating across protocols.
Inference, not tested here: more sweat lost during a swim, where evaporation does little cooling, is fluid lost for no thermal gain.
Not from this paper: pooled topical evidence is in REF-963; the base's protocol and safety caveats are in SYNTH-25.

Limitations

n=8; sex not stated; no blinding possible with gel vs no gel, and no placebo gel.
With eight athletes the confidence interval for the time-trial difference is wide (-222 to 88 s); the trial cannot exclude a moderate effect in either direction.
Swim plus bike only, no run; one water temperature and one environmental condition.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

crossover, n=8; the comparison is gel vs no gel, so it is not blinded