Using Temperature for Performance, Brain & Body Health
Summary
Dr. Craig Heller, Professor of Biology at Stanford University, explains the science of thermoregulation and how the body heats and cools itself. He reveals that most common cooling strategies (ice packs on the neck, cold towels on the torso) are not only ineffective but can be counterproductive. The key insight is that specialized skin surfaces on the palms, soles of the feet, and upper face are the body’s primary heat exchange portals, and targeting these can dramatically improve athletic performance and endurance.
Key Takeaways
- Muscle failure is largely a heat problem: A temperature-sensitive enzyme shuts off fuel delivery to mitochondria when muscle temperature exceeds ~39–39.5°C, causing muscular failure before glycogen is depleted.
- Cooling the wrong places can backfire: Applying cold to the torso, neck, or head can trigger vasoconstriction of the body’s natural heat-loss portals, trapping heat and potentially worsening hyperthermia while making you feel cooler.
- The glabrous skin portals are the key: Hairless skin on the palms, soles of the feet, and upper face contains arteriovenous anastomoses (AVAs) — direct artery-to-vein shunts that bypass capillaries and allow rapid heat exchange.
- Cooling these portals between sets can double or triple work volume: A professional NFL tight end went from 40 dips per session to 300 dips per session over four weeks of palm cooling between sets.
- Gains are real and permanent: The increased work volume from cooling produces true muscular conditioning — the strength and size improvements are retained even when cooling is no longer used.
- Cooling eliminates delayed onset muscle soreness (DOMS): Subjects who cooled properly after high-volume workouts reported significantly less or no muscle soreness the following day.
- For hypothermia recovery, heat the portals — not the torso: Warming the hands and feet reheats the body far more efficiently than warm blankets on the trunk; one clinical prototype warmed hypothermic post-surgical patients in ~8 minutes using this principle.
- Ice-cold is counterproductive: Water or objects that are too cold cause reflex vasoconstriction of the AVAs, sealing heat inside the body rather than releasing it.
- Pre-exercise cooling increases heat absorption capacity: A brief cool shower or immersion before aerobic exercise lowers core temperature, giving the body more thermal headroom before performance degrades.
Detailed Notes
How the Body Regulates Temperature
- The body’s thermostat resides in the preoptic anterior hypothalamus, which collects averaged thermal input from the entire body surface.
- Cooling the skin surface (e.g., with an ice pack or wet towel) sends false signals to the hypothalamus — like placing a cold cloth over a thermostat — causing it to reduce heat dissipation even as core temperature rises.
- Normal body temperature is ~37°C, but peripheral tissues (hands, arms) operate significantly cooler than core temperature.
- Core temperature is best measured esophageally in a lab setting; tympanic (ear) measurement is the most practical field alternative. Forehead infrared measurements are crude but better than skin measurements elsewhere on the body.
Why Muscles Fail During Exercise
- The body is approximately 20% efficient at converting food energy to work; the remaining ~80% is lost as heat.
- During anaerobic activity, muscle metabolism can increase 50–60 fold, but blood flow cannot keep pace — meaning heat accumulates faster than it can be removed.
- A temperature-sensitive enzyme involved in shuttling glucose metabolites into the mitochondria shuts off at approximately 39–39.5°C.
- This is the primary and fastest mechanism of muscular fatigue — not glycogen depletion or oxygen deficiency.
- Systemic core temperature rise also impairs cognitive performance; subjects on a treadmill begin to lose the ability to perform simple arithmetic around 39°C.
The Glabrous Skin Portals (AVAs)
- Arteriovenous anastomoses (AVAs) are direct shunts from arteries to veins that bypass capillaries, allowing very high blood flow rates with low resistance.
- Located in evolutionarily hairless skin: palms of the hands, soles of the feet, and upper face (above the beard line).
- These are the body’s primary radiators — visible as redness in warm palms; squeezing a glass causes blanching when AVA flow is compressed.
- Gripping objects tightly (e.g., bicycle handlebars, a phone while running) compresses these vessels and impairs heat loss, reducing performance.
- Wearing gloves and socks also impedes heat loss from these portals.
Common Cooling Mistakes
| Common Practice | Problem |
|---|---|
| Ice pack to back of neck | Cools blood to brain → thermostats reads “cool” → reduces heat dissipation; core temp can continue rising |
| Cold towel on torso | Causes vasoconstriction of AVA portals; reduces heat loss rate |
| Ice vest | Same mechanism — feels good but impairs natural radiators |
| Hand in ice water | Triggers reflex vasoconstriction of palmar AVAs; seals in heat |
| Sponge over head during sport | Temporarily suppresses thermostat; athlete feels recovered but is still hyperthermic |
Optimal Cooling Protocol (Performance)
- Target: Palms of hands, soles of feet, upper face
- Temperature: Cool but not ice cold — cold enough to draw heat but not so cold as to trigger vasoconstriction. The CoolMitt device operates at a specifically calibrated cool (not freezing) temperature.
- Duration: ~3 minutes between sets; heat loss follows an exponentially declining curve — the biggest benefit occurs in the first 2–3 minutes.
- Verification test for improvised cooling: After holding a cold pack, have someone feel your palm. If it’s cold, vasoconstriction has occurred and the portal is closed. If still warm, blood is flowing and cooling is working.
- Improvised options: Frozen peas or a cool (not frozen) object passed between hands during rest periods. Avoid gripping too tightly or for too long with frozen objects.
Performance Results from Palm Cooling
- Dips (NFL athlete Greg Clark): Baseline ~40 dips/set × 5 sets → 300 dips/session after 4 weeks of cooling (3× increase).
- Pushups (female college students, non-athletes): Some reached over 800 total pushups in 10 sets with cooling.
- Endurance (treadmill in heat, ~40°C ambient): Cooling during exercise doubled endurance in a naive group of ~18 subjects.
- Golf (Department of Defense test): Special operations soldiers reported adding 20 yards to every club in their bag after using the technology.
- Multiple sclerosis patients: Individuals who were heat-sensitive and restricted from outdoor activity were able to return to golfing in summer using the cooling device on their cart.
- Pre-exercise cooling for aerobic performance: Lowering core temperature before a run extends the time before overheating and the point of sweat induction, allowing either greater speed or greater distance.
Warming a Hypothermic Person
- Standard medical practice (warm blankets, heat lamps on torso) is slow because hypothermia causes vasoconstriction, blocking heat transfer to the core through insulating skin and tissue.
- Correct approach: Apply warmth to the glabrous skin portals — especially the hands and feet — to drive vasodilation and heat directly into the bloodstream.
- A prototype device applying gentle negative pressure (suction) to an arm with a heating pad warmed post-surgical hypothermic patients to normal core temperature in ~8–9 minutes vs. 1–2 hours with standard blanket treatment.
- For home/field use: warm water pads or warm (not scalding) objects placed on the feet and hands are more effective than trunk warming.
Implications for Equipment and Gear Design
- Running: Loose grip, open hands when possible; barefoot running may have worked partly by improving heat dissipation through the soles.
- Cycling: Periodically release grip on handlebars to restore palmar blood flow.
- Helmets: Should be ventilated to prevent