What Are Those Devices Basketball Players Are Holding on the Sidelines?

Some sports equipment is self-explanatory. Few people need an explanation for why football players wear helmets, or why it’s a better idea to catch a baseball with a leather glove than a bare hand. But recently, a peculiar-looking device has prompted curiosity among spectators—a wine bottle-shaped tool gripped by athletes during rest periods at basketball games. It’s also popped up at NFL and NHL contests.

What they’re clutching is the latest in sports science known as a palm cooler.

Made by a variety of manufacturers, the product is meant to reduce the physiological effects of exertion. The athletes holds on to copper tubes or other material much cooler than the ambient temperature: Between 45 and 60 degrees Fahrenheit. (Too cold, like a can of soda, and you wind up constricting blood vessels.) As warm blood passes through the hand, it’s cooled down. In theory, this rapidly cools the entire body, aiding in recovery and facilitating improved endurance.

While it might seem to flirt with pseudoscience, the idea of palm cooling has support from Stanford researchers. In the early 2000s, the university began exploring ways to bring down the core body temperature of soldiers stationed in Iraq. Building on thermal regulation observed in animals like bears, which release heat through their paws, the work led to the idea that body heat could be brought down via glabrous skin surfaces harboring plenty of rapidly-dilating blood vessels. By cooling palms, you cool the entire body.

By 2020, a startup dubbed CoolMitt—which framed the concept as a literal mitt to be worn, and backed by Stanford’s researchers—was first to market. That was followed by other manufacturers, including Apex Cool Labs, which markets a $399 pair of Narwhals. Those are the wine bottle-shaped devices seen at the 2024 NCAA women’s basketball finals, among other sporting events.

Apex claims that 1 to 3 minutes of cooling “reduces heart rate and extends a player’s ability to sustain a higher intensity of play longer.” Ten minutes can reduce core body temperature by one-half a degree Celsius. Anecdotally, athletes report a slower heart rate, better cardio, and even some mental benefits.

But as with many novel athletic devices, there’s some skepticism. Research is encouraging but limited in scope. One 2012 Stanford paper on palm cooling in resistance training, for example, recruited only 67 subjects. And not all research is glowing: A 2023 study published in The International Journal of Sports Medicine found no difference in runners who palm-cooled and those who did not.

According to The New York Times, the United States Tennis Association wants to see more sport-focused research before permitting the CoolMitt at the U.S. Open. CoolMitt is now working with USA Cycling to evaluate the strategy on bicyclists.

Despite some doubt, palm coolers are gaining momentum in professional sports as well as other fields. Firefighters in Loudoun County, Virginia, have purchased Narwhals to help first responders cool down when overheated by their heavy and bulky protective gear. Advocates also see potential for palm coolers in hospital settings or at events like marathons or outdoor gatherings where heat-related illness is a concern. In all likelihood, you'll be seeing a lot more athletes embracing them in the future.

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