Summary
Dr. Andrew Fix hosts Dr. Kyle Sella, a physical therapist and strength coach who founded AVA Cooling Technology, for a deep follow-up on palmar cooling. Sella explains the science behind glabrous skin on the palms, soles of feet, and face, where arteriovenous anastomoses (AVAs) allow rapid heat exchange. He discusses how cooling the palms between sets can reduce core temperature, lower heart rate faster, and allow athletes to sustain more training volume over time. The episode covers real-world applications across youth sports, sedentary populations, firefighter recovery, and professional teams like the Denver Nuggets. Sella also critically analyzes two 2023 studies from the Journal of Strength and Conditioning that found no benefit from palmar cooling, arguing their methodology was flawed: only four sets of bench press at 80% 1RM with three-minute rest periods did not generate enough volume or accumulated heat to reveal a difference. He references the Stacey Sims Stanford study showing sedentary obese females who palmar cooled during treadmill intervals exercised more and improved across all outcomes over 12 weeks. Optimal cooling temperature is 45-60 degrees Fahrenheit -- cool enough to transfer heat but not so cold it triggers vasoconstriction.
Key Points
- Glabrous skin on palms, feet, and face contains arteriovenous anastomoses (AVAs) that allow rapid heat exchange with the body's core
- Palmar cooling works best during high-volume or short-rest training where heat accumulates -- not during low-volume, long-rest protocols
- Optimal cooling temperature is 45-60 degrees Fahrenheit; too cold triggers vasoconstriction and shuts down the heat-exchange mechanism
- Two 2023 JSCR studies finding no benefit used only 4 sets of bench press with 3-minute rest and applied cooling for only a fraction of rest time -- insufficient to test the real claim
- Stacey Sims' Stanford study showed sedentary obese females who palmar cooled during treadmill intervals did more exercise and improved across all measured outcomes over 12 weeks
- Firefighter forearm submersion studies show faster heart rate recovery, likely driven by palm contact with cool water
- Heat is a primary driver of fatigue at all fitness levels -- the hypothalamus reduces motivation as core temperature rises
- Professional teams (Denver Nuggets, Borussia Dortmund) and youth sports programs are adopting palmar cooling
Key Moments
How glabrous skin and AVAs enable rapid core cooling through the palms
Kyle Sella explains the anatomy behind palmar cooling: glabrous skin on palms, feet, and face lacks hair follicles and contains arteriovenous anastomoses (AVAs) that connect arteries directly to veins, enabling efficient heat transfer.
"And underneath glabrous skin are a special network of vessels called ABAs or arterial venous anastomosis. And again, think back to those. Those are like where arteries and veins connect directly without a capillary involvement. And that circuit in high dense, those circuits and high densities under that glabrous skin allows us to really dump heat or accept heat really effectively or inefficiently through those, those areas of glabrous skin."
Why cooling too cold backfires -- vasoconstriction shuts down heat exchange
Ice-cold temperatures trigger vasoconstriction in the palm's blood vessels, blocking the heat-exchange mechanism. The ideal range is 45-60 degrees Fahrenheit -- cool enough to transfer heat but not so cold it triggers a neural protective response.
"if I add freezing cold temperature to my palm and it feels uncomfortable, we may be getting some vasoconstriction there and then we're not circulating that blood."
Stacey Sims study -- sedentary obese women who palmar cooled exercised more and improved across all outcomes
A Stanford study by Dr. Stacey Sims found that sedentary obese females who palmar cooled between treadmill intervals over 12 weeks did significantly more exercise and improved across every measured outcome compared to the non-cooling group.
"At the end of the 12 weeks, the Palmer Cooling Group actually did more exercise and they improved significantly compared to the other group in every outcome that they were measuring."
Why 2023 studies failed to detect palmar cooling benefits -- a methodological critique
Sella breaks down two 2023 JSCR studies that found no benefit from palmar cooling, explaining they used the same 11 subjects, only 4 sets of bench press at 80% 1RM, and three-minute rest periods -- not enough volume or accumulated heat to reveal a difference in work output.
"The combined findings of both papers state that palm curling cooling had no observable effects on physiologic metabolic responses during exercise, nor has it any effect on bench press performance."
Shorter rest intervals magnify palmar cooling benefits -- 28% volume improvement at one-minute rest
Sella shares his self-testing results: with three-minute rest periods he saw a modest 15% volume improvement, but switching to one-minute intervals produced a 28% jump -- because less natural recovery means the cooling intervention has a bigger relative effect.
"After three minutes, I felt pretty dang rested. I had a fatigue curve for sure, but I felt pretty dang rested. I had a 15% bump from one day to the next."
