The mood during the second half of the 2024 NCAA women’s basketball national title game was predictably intense.
In what would later be revealed as the most-watched women’s college game of all time, the undefeated South Carolina Gamecocks were looking to close out a perfect season against Iowa and superstar Caitlin Clark. The score margin had rarely left single digits. Players on both squads were leaving everything on the floor.
As Gamecocks coach Dawn Staley instructed her team during time-outs, trainers passed around the typical things athletes need to recover from an intense effort: water bottles, towels, sports drinks. Also being passed around, though, were handheld devices featuring a metal container and copper extensions, which several SC players held at each break. These thick black cylinders had small copper tubes coming out of their tops, tapered off to look almost like an oversized wine bottle being held by its neck.
These are “palm-cooling” devices called Narwhals, so named for their visual similarity to the protruding tusks of narwhal whales. They’re made by Apex Cool Labs, one of several companies manufacturing these types of devices, all of which are designed to rapidly cool an athlete’s palms. Gripping the copper tubes initiates a sort of physiological trick: When you cool the palms (or foot soles) of a human who’s stressed from exertion, their core temperature drops as well. Their heart rate normalizes more quickly, and they can bounce back from heat stress more effectively and in less time.
Gamecocks point guard Raven Johnson says the entire team uses the Narwhals, during both games and practices. The devices are especially helpful for high-volume players like Johnson, who led the team in court time all season and played 37 of a possible 40 minutes in that national title game last April, helping South Carolina eventually pull away for a win to top off an unbeaten championship season.
“When you put your hands on it, it cools you down,” Johnson says. “It literally slows my heart rate down. It helped me with my breathing.”
Palm cooling, also known as palmar cooling or vasocooling, was discovered over 20 years ago by Stanford University researchers. But it didn’t find its way into the mainstream until recently.
High-level athletes across numerous sports have begun adopting palm cooling as a training and recovery tool to fight against the known effects of heat stress on the body—effects that are only growing more significant as climate change makes conditions hotter across many sports. They’re not the only ones looking to chill; both clinical research and a growing body of anecdotal evidence suggest the technology is beneficial across a wide range of heat-stressed fields, including firefighting, industrial work, and the medical world. Many of palmar cooling’s proponents believe it’s primed for an even bigger explosion. “I think it can go worldwide, honestly,” Johnson says.
Is palm-cooling technology a legitimate tool to combat heat stress in a warming world, one that could someday be as ubiquitous as Gatorade or cooling fans? Or is it just another fad that will pass once the hype dies down?
When the US military needed a portable way to cool overheated personnel in Iraq in the early 2000s, it turned to a team of Stanford University researchers led by biologists H. Craig Heller and Dennis Grahn.
Heller and Grahn had related experience: They had previously researched the thermal mechanisms of bears, who radiate heat via the non-furry skin on the pads of their feet. The researchers realized humans have similar functions in their palms, foot soles, and parts of the face, known collectively as “glabrous” skin areas, which are hairless and contain blood vessels that dilate and contract quickly and widely. The team hypothesized that temperature could rapidly be extracted from the vessels in these areas. Armed with Darpa funding, they set to work developing devices to extract heat from these glabrous skin areas, primarily via the palms for convenience reasons.
They performed a range of studies across several years, often using Stanford student athletes or professionals who lived in the area as test subjects. Several early discoveries would set the foundation for palm-cooling devices moving forward.
One was the ideal temperature range of the palm-cooling device. A common query from people newly exposed to palm cooling reads something like, “Why can’t I just grab a soda can from the fridge and hold onto that?” If the part that comes in contact with the skin of the palm is too cold, the blood vessels in the palm meant to dilate and increase blood flow will instead constrict, causing the opposite effect. Most of today’s palm-cooling devices target a consistent temperature range of somewhere between 45 and 60 degrees Fahrenheit.
The Stanford team had issues bringing a consumer product to market for much of the 2010s, due to both lack of demand for palm-cooling devices and limitations with their designs. But in 2020, former Navy member and ex-basketball player Craig Gile cofounded CoolMitt, a company that licensed the Stanford patents and brought Heller and Grahn in as advisers.
CoolMitt quickly set the standard for palm-cooling devices when it hit the market. Updated models have since appeared, including a design with a still-unique palm insertion method that requires no actual gripping from the user. The mitt just slips onto the wearer’s hand. (The company’s signature CoolMitt costs $995. Narwhals are cheaper, $399 for a set of two.)
All these devices work similarly. Users either grip or insert their hand into the device when in a heat-stressed state. They maintain this position for a set amount of time as they rest—it could be as little as 30 seconds or as long as several minutes. As blood passes through the palm, the device extracts heat and returns cooler blood to the rest of the body. Most athletes hold the device in one hand, while some are designed to be held by both hands. Pricier devices like CoolMitt are designed to stay at the target temperature for long periods, while less expensive options need to be recooled after an hour or so.
Even as palm-cooling products proliferated, mainstream adoption was slow. But once many of the world’s best athletes and trainers started incorporating these gadgets into their recovery routines, that started to change.
Between periods of a game during the Edmonton Oilers’ run to the Stanley Cup Finals in June of last year, the Hockey Night In Canada broadcast cut to a shot of star Connor McDavid in the locker room. Legendary host Ron MacLean noticed teammate Zach Hyman sitting beside McDavid with an intently focused look on his face, holding onto strange-looking items with both hands. MacLean wondered aloud, almost with a chuckle: “What is Zach Hyman doing?”
You guessed it: He was palm-cooling.
Hyman is one of several Oilers players who uses Apex’s Narwhals, and not just between periods—they’re even used on the bench in between player shifts. The Oilers experimented with other devices, including CoolMitt, but found the Narwhals more affordable and convenient. (That bottle-like shape comes in handy; the Narwhals fit into the water bottle slots that sit in front of players on the bench.)
“I really enjoyed using the palm coolers, especially in warmer climates like Dallas and South Florida,” Hyman told WIRED in an email. “When you get into May and June, the buildings become hotter to play in. I found the palm coolers helped in cooling my body temperature down.”
Columbus Blue Jackets forward James van Riemsdyk was intrigued when he first heard about palm cooling through a performance coach. It didn’t even take him a full game to see the benefits.
“The first game I used it, going into the second and third period, I noticed a difference,” van Riemsdyk says. “I just felt a little clearer mentally, then physically felt a little bit less heavy or fatigued as the game went on … It made me a believer.”
Van Riemsdyk has used the tech ever since, including through a team change this past summer.
Palm cooling can now be found across virtually every major sport. It’s used by NBA, NHL, MLB, and NFL players and teams, plus in tennis, soccer, and several Olympic sports. The USA Wrestling team brought a CoolMitt with them to the 2024 Paris Summer Olympics, using it for athletes between matches. Some of the biggest names in athletics, from Novak Djokovic and Joel Embiid to Katie Ledecky and Nolan Arenado, have been spotted using palm-cooling devices.
Users I spoke to reported improved endurance, slowed heart rate, and several similar effects from using the devices. Many of these claims are backed up by limited but convincing clinical research. For many, the effects are virtually immediate.
“I [felt] it right away, as soon as [sports performance coach Molly Binetti] handed it to me,” says MiLaysia Fulwiley, a guard for South Carolina women’s basketball team. Fulwiley had been struggling with labored breathing and fatigue during game timeouts before trying the Narwhals. “I wrapped my hand around it, and my heart just started beating a little slower. It made me be able to breathe.”
Some users even report mental benefits from palmar cooling, though there’s little research to suggest the technique has any calming psychological effects. Palm cooling seems to offer a sort of centering effect for certain athletes; not relaxation, per se, but a grounded sensation. “It makes it easier for me to concentrate and focus on what [Coach Staley] said [during a timeout],” Fulwiley says.
Palm cooling’s purported benefits likely raise the most eyebrows in strength-training fields. Some research has suggested palm cooling can provide effects similar to or even greater than anabolic steroids for muscle recovery and subsequent volume increases among strength trainers. This is easily the most controversial claim the Stanford team makes, but they stand by it even despite the skepticism it draws in some circles.
“Why would you use an inferior method that’s illegal and is not healthy,” Heller posits, “when you can get much greater benefits and effects with a system which is not going to jeopardize your health and is perfectly legal?”
Whether those claims hold water may ultimately be irrelevant for palm cooling’s future, where many of its most fascinating potential uses don’t involve sports at all.
When firefighters in Loudoun County, Virginia, hit a certain time limit for work inside a major fire or related threat situation, they enter a unit called Rehab 623 for cooling and recovery. They must meet temperature, blood pressure, and pulse rate benchmarks to return to duty; if they fail to do so, it often results in hospitalization.
Captain Scott Lantz says Rehab 623 is outfitted with over two dozen Narwhals from Apex, among other cooling tools. The department also uses the units for various training exercises, which often involve entire days spent wearing heavy protective gear. Palm cooling has had a remarkable impact.
“I don’t think there’s anything we’ve used that can even touch this,” Lantz says. “The cost of use per time is not high. It’s probably about the price of a Gatorade. If you look at the [research] that has been done, it’s pointing to yes, it really does work, it’s not just a placebo effect.”
That research is incredibly wide-ranging. The studies suggest palmar cooling shows benefits for everything from multiple sclerosis and menopausal hot flashes to various industrial use cases. The Stanford team has tested a fully portable in-suit palm-cooling method meant for Ebola treatment doctors in Africa, with positive initial results. AVA Cooling, a company offering a $70 device—much less expensive than CoolMitt or Apex—has developed a sleep protocol for people who struggle to relax after late-night sports or workouts. The protocol involves an initial cycle of cooling using the soles of the feet, then a second using the palms just before bed.
One study showed that placing hospital cold packs on glabrous skin—the skin targeted by palm cooling—cooled overheated test subjects at nearly twice the rate of standard medical cooling methods. This trial included only 10 participants, however, and some other studies utilized similarly limited samples.
Heller bemoans a lack of larger-sample research or even adoption of this approach in the medical world and several related settings–such as high school gyms, which contain defibrillators but nothing for rapid body cooling.
“How many high school students have heart attacks? Not very many,” Heller says. “But how many student athletes in high schools come down with heat illness, heat stroke, even heat death?”
There’s certainly skepticism to be found, including recent research suggesting limited or no benefit from palm cooling. Virtually everyone surveyed for this story agrees more direct and high-volume research is needed. The subjects are out there: From athletes across numerous sports to firefighters, from construction workers to medical patients and personnel. There are even larger populations available at mass participation events like outdoor ceremonies or large sporting events, where fans often experience heat stress or even heat stroke.
Many of these sectors are already utilizing palm cooling. Apex estimates around 10 different fire departments nationwide use their Narwhals, and CoolMitt says they’ve sold to 25 departments. CoolMitt provides products across several branches of the military (one Navy SEAL trainer even wrote a blog post highlighting CoolMitt’s benefits).
Even skeptics would concede there are no known negative side effects or injury risks associated with palm cooling. In a world that’s only getting warmer, the space seems ripe for more exploration.
“I definitely think it can be revolutionary and change how we view working in hot environments,” Lantz says.
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