Menthol.

A carbohydrate-electrolyte drink addresses fluid and sodium replacement, a physiological input, while menthol acts on cold receptors and changes how the drink and the heat feel. Those are different targets, which is exactly why the combination was tested. The reported effects sit on hydration and recovery measures, and thermal perception is a perceptual endpoint rather than a measure of core temperature.

Caffeine antagonises adenosine receptors and lowers perceived exertion through a central route. Menthol works peripherally at TRPM8 cold receptors in the mouth and skin, changing thermal sensation without lowering core temperature. Because the routes are separate, the perceptual effects can add. Neither one is cooling the body, and that distinction matters when heat strain is the actual risk.

Peppermint oil is largely menthol by weight alongside menthone, menthyl acetate and cineole. Taking both means taking menthol twice, which is worth knowing when a product lists them separately. Peppermint oil also relaxes the lower oesophageal sphincter, which is why enteric coating exists for gut-directed use and why reflux is the common complaint with uncoated capsules.

Capsaicin activates TRPV1 and produces a burning sensation; menthol activates TRPM8 and produces cooling. Applied together they compete perceptually, and topical products that combine them are exploiting the confusion rather than the sum. There is also cross-desensitisation between the two channel populations, so repeated exposure to one blunts the response to the other.

Camphor activates TRPV3 and at higher concentrations desensitises TRPV1, while menthol drives TRPM8. Together they produce the layered warm-then-cool sensation typical of rub preparations. This is a sensory and counterirritant effect on skin, not an anti-inflammatory action on the tissue underneath.

Gingerols and shogaols activate TRPV1, the warm channel, producing a warming oral sensation. Menthol drives the cold channel in the opposite direction. Taken together during heat exposure the perceptual effects work against each other, which is a reason not to combine them in a pre-exercise mouth rinse.

Sodium bicarbonate acts as an extracellular buffer against the acidosis of high-intensity work, a chemical effect with nothing to do with thermal perception. Menthol changes how the effort and the heat feel. The practical link is palatability: bicarbonate tastes unpleasant and menthol is sometimes used to mask it, which is a flavour role rather than an ergogenic one.

L-theanine affects central measures such as alpha wave activity and subjective calm through a slow oral route. Menthol acts within seconds at peripheral cold receptors in the mouth. Nothing has tested them together, and the pairing rests on the observation that they operate on different timescales and different systems.