That prickly sensation on the top of my skull? It’s just a couple of milliamps of positive electric current, roughly the same amount used to power your average household smoke alarm, flowing directly into my brain’s motor cortex. Suffice it to say: I’m a little uneasy about it.

I’m sitting in a windowless lab, quietly gazing at stark white walls as my head continuously absorbs the tiny electric pulses. No matter how hard I try, I can’t shake the image of a young Jack Nicholson thrashing his way through electroshock therapy in One Flew Over the Cuckoo’s Nest. But unlike his electric current, mine is actually deemed safe, and the man administering my treatment is no Nurse Ratched. His name is Aaron Wayne. A former captain of Stanford’s swim team, Wayne works as a research engineer for San Francisco–based Halo Neuroscience. I’m testing out the Halo Sport: a set of earphones—lined with rubbery spikes—that, the company says, supercharges your brain for the sake of fitness.

I’m also exercising. With the headset firmly on, I’m seated at a specialized curl machine with a few electrodes attached to my arm to measure my power output. Every time I do a curl, a blue line on a computer screen across from me jags up to a peak when I lift and drops off when I finish. 

Wayne performs tests like this one all day on subjects, trying to understand how Halo’s technology affects different kinds of exercise. In the five years since Halo launched, the company has run more than 125,000 test sessions. Those test sessions, the company says, have produced clear, positive results. The Halo Sport may already be on sale to the public ($749;, but its first users haven’t been your average gymgoers. So far, Olympians, NFL and MLB players, top trainers, and even members of the U.S. military’s special forces have adopted it.

Electrifying Headphones
Courtesy of Halo

The Future of Training

Created by a Stanford-trained M.D. named Daniel Chao, Halo uses a process called transcranial direct current stimulation (tDCS)—neuroscience-speak for sending a low electric current into a targeted part of the brain and exciting the neurons, thus making them more likely to fire and create new neural pathways. This, in turn, makes the brain temporarily better at hard-coding what you’re doing. So when you stimulate the motor cortex—the part of the brain that controls movement— and pair that stimulation with a workout, you get better at the exercises in that workout, and more quickly than you would otherwise.

“Most people think the brain’s role in exercise has to do with the mechanics of precise skill, like shooting a free throw or putting a golf ball,” Chao says. “That’s true—skill is neurologically governed. But what about how strong we are? When people do strength training by lifting weights, they think it’s all about the muscles. But with repetition, you’re also training the brain to master those movements.” In other words, strength isn’t just about how big your muscles are but how well you control them. The Halo Sport, Chao says, sharpens that process and essentially makes your workouts better and more efficient. As a result, you’ll get stronger and bigger a whole lot faster. 

It sounds crazy, I know. But thousands of independent studies have examined tDCS in the past 15 years and shown positive effects on everything from memory to mood disorders, depending on what part of the brain you zap. “It’s not just about getting stronger faster. It’s about learning faster,” Chao says. “Theoretically,” says Vince Clark, director of the University of New Mexico’s Psychology Clinical Neurosciences Center, “[the Halo Sport] should work.” Which raises a question: What can it do for you?

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Upgrade Your Brain

Hours before my headset test, I’m chasing Chao up a San Francisco hill on a road bike. A passionate cyclist, he appointed himself one of Halo’s first test subjects when he started developing it.

With the Halo Sport, he started doing interval training on a stationary bike and pounding out laps at the cycling oval in Golden Gate Park. Just north of the Golden Gate Bridge is Hawk Hill, which Chao had long failed to climb in less than eight minutes. “So one day I decided to give Hawk Hill a go again, and my time was 7:45. To make sure it wasn’t a fluke, I did it again—I wanted to cement that puppy.”

Chao grew up in Anaheim, CA, studied biochemistry at UC Berkeley, and earned a master’s and an M.D. at Stanford, where he also caught the Silicon Valley start-up bug. “When I think about my entrepreneurial friends, many of us can identify a kind of fuck-you moment, when something led us to say, ‘Why is it like this? We should be doing it entirely differently.’ ”

For Chao, that moment came during pharmacology class, when he was learning about drugs for the brain. “They all suck,” he says. “You have to put up with a bunch of side effects to get the benefit.” Unlike other organs, the brain is protected by a so-called blood-brain barrier, which makes it difficult for drugs to get through. So Chao thought to himself: “The brain is an electrical organ; why not speak its language and use electricity to affect it?” He landed a job at a biotech start-up called NeuroPace, which made an implantable device to treat epilepsy with deep-brain electrical stimulation. After years of pursuing the “long, arduous journey of working with the FDA,” NeuroPace got approved, but by then Chao and a co-worker, Brett Wingeier (now co-founder of Halo), felt another fuck-you moment coming on.

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They’d been paying attention to a growing body of research showing that electrical stimulation from outside the head—tDCS—could affect the brain’s performance in other ways, and with big results. So they started testing potential tDCS products by targeting different brain functions. Eventually, they created a set of headphones that buzzes that area. And for the record, you wear the Halo Sport before a workout, not during. “A typical use would be to wear it for 20 minutes while warming up,” Chao says, “then take it off and feed the brain as many quality reps as possible over the next hour.”

To test the device, the founders turned to 10 top college athletes who trained at Michael Johnson Performance (MJP) in Texas. The athletes used the Halo Sport while doing a five-week lower-body strength program and saw a 12% gain in explosiveness, compared with a mere 1.7% for a control group.

Halo will “rewrite the way we think about training the body by focusing on what we can do above the neck,” says Lance Walker, MJP’s global director of performance. As for the safety? “We simply don’t know,” says Clark, the UNM neuroscientist. “There are studies that have to be done about the long term.”

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