Using Temperature for Performance, Brain & Body Health | Dr. Craig Heller

Special arterio-venous anastomoses (AVAs) under hairless skin in the palms, soles, and upper face shunt large volumes of blood directly from arteries to veins, enabling rapid heat exchange. Cooling these areas with moderately cool (not ice-cold) surfaces can double endurance in heat and dramatically extend work volume in resistance training, while heating them can rapidly re-warm hypothermic individuals. In contrast, most of the hairy body surface is relatively well insulated and much less efficient for active heat transfer.

Very cold stimuli (like ice water or frozen bottles held continuously) trigger reflex vasoconstriction in the AVAs, effectively shutting down the very heat-loss pathways you're trying to exploit. Heller’s lab found optimal performance gains with cooling surfaces that feel merely ‘cool,’ not painfully cold; in practice, the most effective heat extraction happens within the first 2–3 minutes before vasoconstriction kicks in. A simple self-check: if your palm feels cold to another person after cooling, you likely overcooled and constricted the vessels.

Lowering core temperature slightly before endurance efforts (e.g., cool shower, brief portal cooling after warm-up) increases the body’s ‘heat sink’ capacity so you can run or work longer before temperature becomes limiting. For anaerobic work like dips, push-ups, or squats, localized muscle temperature can skyrocket while blood flow cannot increase proportionally, risking ‘cooking’ the muscle and enzyme shutdown (e.g., temperature-sensitive pyruvate kinase). In controlled experiments, 2–3 minutes of palm cooling between sets led to doubling or tripling total work volume over weeks, with significant performance gains retained even when cooling was later removed.

Cooling the neck, head, or torso strongly stimulates skin temperature receptors that feed into the hypothalamic ‘thermostat,’ making you *feel* cooler while core temperature may continue rising. In field studies, cooling standard ‘artery zones’ (neck, armpits, groin) with cold packs was only half as effective at reducing core temperature as placing the same packs on the glabrous skin portals (palms, soles, upper face. Furthermore, cooling the neck can protect the brain transiently but may also trick athletes into resuming hard efforts while still dangerously hot internally.

In multiple experiments, subjects who used palmar cooling between heavy sets vastly exceeded their normal training capacities (e.g., Stanford students surpassing 800 push-ups in one session, an NFL tight end tripling his dip volume to ~300 in a month). Despite acute overreaching, those using cooling reported minimal delayed onset muscle soreness compared to non-cooled controls doing lower volume. This suggests that strategically limiting overheating, rather than total load per se, plays a large role in muscle damage and perceived soreness.