Dr. Craig Heller: Professor of biology and neurosciences at Stanford whose lab studies thermoregulation, Down syndrome, and circadian rhythms. He co-developed palmar-cooling technology and has chaired Stanford's biology department and directed its human biology program.
What this episode covers
Dr. Craig Heller explains how the body heats and cools itself and how core temperature is one of the most powerful limiters of physical and mental performance. He reveals that muscles fail in large part because a temperature-sensitive enzyme shuts off fuel supply when muscles overheat, and that special hairless ('glabrous') skin on the palms, soles, and face contains blood vessels (AVAs) that act as the body's true radiators. Cooling these surfaces, not the neck, torso, or armpits, can double or triple work volume, eliminate delayed-onset muscle soreness, and dwarf the gains from anabolic steroids. He debunks ice packs on the neck and brown-fat-stimulating ice on the upper back, and finishes with insights on hibernating bears, shivering, caffeine, and why a cool sleep environment helps.
Also referenced (named, not recommended)
Gray's Anatomy
Henry Gray
“We didn't discover the blood vessels that are described in "Grey's Anatomy," but nobody knew what they were for.”— guest
Big reveals from this episode
- Muscular failure is driven largely by heat: a temperature-sensitive enzyme shuts off the muscle's fuel supply above about 39 degrees C.
- Cooling the neck, torso, or putting ice packs on the head can be counterproductive, fooling the brain's thermostat and even causing core temperature to rise toward hyperthermia.
- A 49ers tight end doubled his dips in days and tripled his total to 300 in a month using palmar cooling between sets.
- Cooling the palms, soles, and face cools a hyperthermic person twice as fast as the standard ice packs on armpits, groin, and neck.
- Palmar cooling produced roughly 300% strength gains in a month versus the ~1% per week typical of anabolic steroid studies.
- Performance gains from cooling persist even when you later train without cooling: it is a true conditioning effect.
- Human brown fat is distributed with regular fat, not concentrated between the shoulder blades, so ice packs on the upper back mostly chill the vertebral arteries to the brain.
- Caffeine, as an adenosine antagonist, may actually reduce blood flow and oxygen delivery to working muscle, potentially hindering performance.
Worth remembering
- A cold shower causes vasoconstriction that can make it harder for the body to shed heat, while full immersion overrides this via huge surface area.
- Muscle metabolism and heat production can rise 50 to 60-fold during anaerobic activity, while blood flow cannot, so you can literally 'cook' your muscles.
- We are only about 20% efficient; roughly 80% of food energy is lost as heat, like a steam engine.
- Heat-loss portals sit in glabrous (hairless) skin: human palms, soles, and upper face; rabbit ears; bear tongues.
- Cool blood from the face can reverse direction through skull vessels to actively cool the brain, explaining why pouring water on the head works.
- A negative-pressure hand-warming prototype restored a post-surgery hypothermic patient's core temperature in about eight minutes versus the usual one to two hours.
- In a class experiment, some female students reached over 800 pushups across 10 sets when using cooling.
- Hibernating black bears only drop to about 33-34 degrees C and shiver to stay there, while ground squirrels can drop near freezing.
- Tapping your foot wastes about four times the movement's energy as heat, illustrating non-exercise thermogenesis.
- A cool bedroom helps sleep because you can passively thermoregulate by sticking out your hands and feet, your natural heat-loss surfaces.