Increase Strength & Endurance with Cooling Protocols
Summary
Dr. Craig Heller, professor of biology at Stanford University, explains how body temperature regulation directly limits physical performance — both aerobic and anaerobic. He details how specialized heat-loss portals in the palms, soles of the feet, and upper face can be strategically cooled to dramatically increase work capacity, and presents research showing cooling protocols can double or even triple performance output.
Key Takeaways
- Local muscle overheating — not just systemic fatigue — is one of the primary causes of muscular failure during resistance training.
- A temperature-sensitive enzyme that fuels the mitochondria shuts off above 39–39.5°C, cutting fuel supply and causing failure.
- The palms, soles of the feet, and upper face are the body’s primary heat-loss portals due to specialized arteriovenous shunt vessels beneath hairless (glabrous) skin.
- Cooling these portals between sets (approximately 3 minutes) can double or triple total training volume.
- Ice-cold exposure is counterproductive — it triggers vasoconstriction of the portals, sealing heat inside the body.
- Cooling the neck, torso, or back of the head can trick the brain’s thermostat, creating a false sense of coolness while core temperature continues to rise.
- A cool shower before aerobic exercise increases the body’s heat-absorption capacity, delaying the point of thermal impairment and improving speed or distance.
- Gripping handlebars or equipment tightly compresses blood flow through palm portals, reducing heat dissipation and limiting performance.
- Cooling gains are real conditioning adaptations — improved work volume translates into lasting strength even when cooling is not used.
Detailed Notes
How Temperature Limits Performance
Aerobic exercise:
- Heat production rises gradually and distributes throughout the body.
- Once core temperature reaches a threshold, performance is impaired.
- Pre-cooling (e.g., a cold shower before a run) increases the body’s capacity to absorb excess heat, delaying that threshold.
- Benefit can be used for greater speed (forcers) or greater distance (pacers).
Anaerobic/strength exercise:
- Core temperature rises slowly, but local muscle temperature climbs rapidly.
- During intense contraction, muscle metabolism can rise 50–60 fold.
- Blood flow to the muscle cannot increase proportionally, creating a heat buildup that cannot escape quickly.
- A key enzyme responsible for delivering glucose-derived fuel to the mitochondria is temperature-sensitive and shuts off above ~39–39.5°C — this is a primary mechanism of muscular failure.
- Even muscles not directly involved in an exercise (e.g., biceps after heavy squats) are affected by the overall rise in body temperature.
The Body’s Heat-Loss Portals
- Located in glabrous (hairless) skin: palms of the hands, soles of the feet, and upper face (above the beard line).
- These areas contain arteriovenous shunts — direct connections between arteries and veins that bypass high-resistance capillaries, enabling high blood flow and rapid heat exchange.
- This is an ancient mammalian adaptation — the only skin surfaces without fur in most mammals.
- Simple test: Squeeze a glass — the palm goes white, indicating blood flow has been compressed. This also explains why tight gripping during exercise reduces heat loss and impairs performance.
What NOT to Do for Cooling
| Method | Why It’s Suboptimal |
|---|---|
| Ice pack on neck/head | Cools the brain’s thermostat (preoptic anterior hypothalamus), creating false sense of coolness while core temp rises |
| Ice vest on torso | Causes vasoconstriction of heat-loss portals, trapping heat |
| Cold towel on quads | Skin and fascia are good insulators; muscle heat only exits via blood |
| Ice water on hands | Too cold → reflex vasoconstriction of palmar portals → seals in heat |
| Cold packs in armpits/groin | Standard medical protocol, but half as effective as cooling palms, soles, and face |
Optimal Cooling Protocol
- Target surfaces: palms, soles of feet, upper face
- Temperature: Cool, not ice-cold — cold enough to draw heat but not trigger vasoconstriction
- Duration: ~3 minutes between sets captures the steepest part of the exponential heat-loss curve
- Verification: After holding a cool object, your palm should feel warm, not cold — warmth indicates the portal is open and blood is flowing; coldness indicates vasoconstriction
DIY approximation: Passing a pack of frozen vegetables (e.g., frozen peas or blueberries) back and forth between hands may provide some benefit. Check that palms remain warm to the touch afterward — if they feel cold, vasoconstriction has occurred.
Commercial device: The CoolMitt (by Arteria; coolmitt.com) is designed to deliver controlled cooling at the optimal temperature with convective circulation, currently used by NFL teams, Olympic athletes, Navy SEALs, MLB, NBA, and the National Tennis Association.
Case Study: Dips with Palmer Cooling
- Subject: Greg Clark, NFL tight end (formerly Stanford)
- Baseline: ~40 dips (set 1), declining over 5 sets with 3-minute rest intervals
- With palm cooling (3 minutes between sets): all sets exceeded baseline; subject reported no fatigue after set 5
- After 4 weeks, twice weekly: increased from ~40 to 300 total dips — roughly a 3x improvement
Endurance Results
- Study with ~18 subjects walking uphill on a treadmill at 40°C ambient temperature
- Continuous palm cooling during exercise doubled endurance compared to no cooling
Long-Term Adaptation
- Increased work volume from cooling leads to genuine physiological adaptations: more contractile elements, muscle hypertrophy.
- Gains are retained even when cooling is not used — it is a true conditioning effect, not a temporary performance aid.