Intermittent sprint performance in the heat is not altered by augmenting thermal perception via L-menthol or capsaicin mouth rinses

PURPOSE: Cooling sensations elicited by mouth rinsing with L-menthol have been reported as ergogenic. Presently, responses to L-menthol mouth rinsing during intermittent sprint performance (ISP) in the heat are unknown and the impact of increased thermal perception on ISP via capsaicin has also not been quantified. This experiment aimed to identify whether eliciting cooling/warming sensations via L-menthol/capsaicin would alter ISP in the heat. METHOD: Fourteen participants (mass = 72 ± 9 kg, [Formula: see text] = 3.30 ± 0.90 L min(−1)), undertook four experimental trials, involving 40 min of ISP in hot conditions (40.2 ± 0.6 °C, 42 ± 2% R.H.) with mouth rinsing (25 mL, 6 s) at the protocol onset, and every 10 min thereafter. Cooling (0.01% L-menthol; MEN), warming (0.2% capsaicin; CAP), placebo (0.3 sham-CHO; PLA), and control (water; CON) mouth rinses were utilized. Performance was quantified via power (PP) and work done (WD) during sprints. Heart rate (HR), core (T(rec)) and skin (T(skin)) temperature, perceived exertion (RPE), thermal sensation (T(sens)), and comfort (T(com)) were measured at 10 min intervals. Sweat rate (whole-body sweat rate) was calculated from ∆mass. RESULT: PP reduced over time (P < 0.05); however, no change was observed between trials for PP or WD (P > 0.05). T(com) increased over time and was lower in MEN (2.7 ± 1.1; P < 0.05) with no difference between CAP (3.1 ± 1.2), PLA (3.2 ± 1.3) and CON (3.1 ± 1.3). RPE, T(sens) HR, T(rec), and T(skin) increased over time (P < 0.05) with no between trial differences (P > 0.05). CONCLUSION: Despite improved thermal comfort via L-menthol, ISP did not improve. Capsaicin did not alter thermal perception or ISP. The reduction in ISP over time in hot conditions is not influenced by thermal perception. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00421-018-4055-0) contains supplementary material, which is available to authorized users.