Palmar Cooling

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."

How AVAs in glabrous skin regulate body temperature

Kyle explains the specialized blood vessel network under glabrous skin — arteriovenous anastomoses that form a direct artery-to-vein circuit without capillaries — and how this system is already used intuitively when we stick a foot out from under the blanket or warm our hands by a fire.

"He was looking at what's called glabrous skin. So glabrous skin is parts of our bodies on the palms of our hands, on the soles of our feet, and like the hairless portions of our face. These are all areas that have like zero hair follicles, right? So there's parts of our body that seem hairless, but you actually, if you look at it, there's little hair follicles. But like on those three areas, like the palms, the soles, and the hairless parts of our face,"

60% improvement in dips with Stanford research

Kyle describes the Stanford dip study showing 60% improvement in total reps, driven by both more reps per set and athletes not receiving the neural shutdown signal, allowing them to keep doing more sets.

"And again, they wouldn't, you know, they would just say, go to failure every set. You're going to take three minutes. You're going to hold, hold onto something cool to dump heat out of, and then you're going to repeat. And they had like a, like something like a 60% improvement in dips done in that workout, which is insane. That's okay. Yeah. If you know anything about working out, yeah. If you've been working out like that, that number just sounds insane. And honestly, to me as a physical therapist and strength coach, you know, I kind of thought it sounded like BS. Like it just seemed like too good to be true. Um,"

Cool not cold — the 45 to 60 degree sweet spot

Kyle explains the critical temperature principle — the cooling surface must be between 45-60 degrees Fahrenheit. Too cold triggers vasoconstriction, shutting down the blood vessels in the palm and blocking the heat exchange.

"if it's freezing cold like your nervous system is going to perceive that as as being too cold and it's going to like vasoconstrict And it's going to shut down those blood vessels in your palm or wherever you're cooling. And you're not going to circulate that. So the trick here is to be like cool, but not cool. So like what we found is like 45 to 60 degrees is like the sweet spot of temperature"

Sleep protocol — using palmar cooling after night games

Kyle describes a sleep protocol used by Boise State basketball where players take the cooled bar home after night games, roll their feet on it, and hold it in bed to lower body temperature faster for better sleep.

"We have a protocol where we have them actually go home, immediately cool their bar. And while they're like, you know, eating or typing or playing video games, they're like rolling their feet on it because that's one of the soles of the feet. Right. And then when they're done, like kind of using their hands and actually get in the bed, they hold on to it for a few more minutes. And we've actually seen like the players are loving it, using it as a sleep aid because it gets their body temperature back down, kind of calms them down."

Glabrous skin and AVAs — the body's heat exchange portals

Huberman explains the three body surfaces with specialized vasculature for temperature regulation — palms, soles of feet, and face — and introduces arteriovenous anastomoses (AVAs) that bypass capillaries for rapid heat exchange.

"You have three compartments for increasing or dumping heat in your body. One is your core. The other is your periphery. But then there's a third component, which is there are three locations on your body that are far better at passing heat out of the body and bringing cool into the body, such that you can heat up or cool your body everywhere very quickly. Those three areas are your face, the palms of your hands and the bottoms of your feet."

100 to 600 pull-ups with palmar cooling

Huberman describes the staggering Stanford data where subjects went from about 100 pull-ups to 180 on day two with cooling, and eventually to 600 pull-ups over several weeks — and could maintain gains even without cooling.

"They started cooling after every other set. The person would just hold the cold tube, cool down the body after every other set. And they found that they went to 180 pull-ups, which is incredible, it's a near doubling. And by doing this repeatedly over several sessions, over several weeks, they quickly went in the cooling group from a maximum of somewhere between 180 and 200 to 600 pull-ups in the equivalent amount of time, which is absolutely incredible."

Palmar cooling outperformed anabolic steroids

The bench press study included a control group on testosterone cypionate. The steroid group improved at about 1% per week, while the palmar cooling group dramatically outpaced them.

"The bench press study was pretty interesting because they actually had a control group that was admittedly taking specific amounts of anabolic steroids. The anabolic steroid was testosterone cipionate, which is essentially testosterone. And indeed the testosterone cipionate, the steroid group improved at a rate of about 1% per week."