Brain stimulation to improve sports performance: does it work?

by Matt de Neef

Improved performance. It’s something cyclists of all levels strive towards, from those just starting out in the sport, to those racing the Tour de France. The process of improvement can be a slow burn — many hours spent training to eke out small advantages, which only get smaller as you get better.

With this in mind it’s little surprise devices like Halo Sport are able to attract attention — devices that promise performance gains, just by doing what you’re already doing. Indeed, if you follow the likes of Greg Henderson, Tayler Wiles or Andrew Talansky on social media, you might have seen these current and former pros posting about Halo Sport, claiming it has helped improve their riding.

So what exactly is Halo Sport? How does it work? Does it lead to the performance gains that these pros suggest? And perhaps most importantly, is it safe?

More than headphones

At first glance, Halo Sport appears to be little more than a pair of large, fancy headphones. But look on the underside of the headphone band and you’ll see three pads of soft electrodes which make contact with the scalp when worn.

Using a technique known as transcranial direct current stimulation (tDCS), these electrodes deliver a weak electrical current through the user’s skull and into their brain, changing the “excitability” of the nerve cells (or neurons) in that region of the brain.

The idea of passing an electrical current into your brain might seem confronting at first but, perhaps surprisingly, it’s a technique that’s been used for nearly five decades now.

Aron Hill has been studying tDCS as part of his PhD in the Therapeutic Brain Stimulation team at the Monash Alfred Psychiatry Research Centre in Melbourne. He explained to CyclingTips that, when used properly, tDCS does seem to effect changes in the brain.

“Typically stimulation is delivered for between 10 and 20 minutes and there’s been a lot of research that’s shown that if you deliver stimulation for that period of time you generally have a window of about an hour where you’ll see a change in brain activity before it returns back to normal,” Hill said. “[There’s] some evidence that if you increase the excitability of neurons in the brain you might get certain behavioural consequences.

“My research, for instance, focuses a lot on cognition. There’s evidence that if you stimulate regions of the brain in the prefrontal cortex — which is the front region of the brain that’s involved in things like memory — you can actually improve people’s memory performance because you’re basically increasing the ability of those brain cells to fire.”

TDCS has also been trialed in a number of medical applications over the years, including for the treatment of schizophrenia (with some success), chronic pain (with little to no success), addictions and craving (some success), Parkinson’s disease and Alzheimer’s disease (with mixed results) and depression (some promising results).

And then there are the potential sporting applications.

Halo’s claims

In the case of Halo Sport, tDCS is used to target the motor cortex — a region of the brain that runs across the top of the head, from side to side. As Dr. Daniel Chao, CEO and co-founder of Halo Neuroscience told CyclingTips, it’s the motor cortex that controls movement in our bodies.

“Activity in the motor cortex moves everything from our eyelids to our quads,” Dr. Chao said. “So what Halo Sport essentially does is it accelerates the motor learning that results from physical practice. What we ask athletes to do is to wear Halo Sport for 20 minutes before their training session. Those 20 minutes of neurostimulation of the motor cortex will induce a temporary state of what neuroscientists call hyperplasticity — or you can think of it as hyper-learning.

“So the movement-based repetitions that you feed the brain while you’re in this state of hyperplasticity will be learned at an accelerated rate.”

So what benefit could this have for cyclists, a sport where aerobic (and anaerobic) fitness is arguably more important than any other factor? We put that question to Dr. Chao, a keen cyclist himself.

“Depending on the distance between your various joints and your flexibility and this kind of thing, there is a most efficient pedal stroke for you,” he said. “Now for most of us it takes a lifetime to find that, if we’re lucky. Now even if you are lucky enough to find it it’s another thing to make it a natural part of your arsenal; something you don’t have to deliberately think about. So how can we help with that?

“There’s a motor learning component to all of that — once you find a more efficient pedal stroke, to what extent can you learn that so that you can go back to it the next time you ride?”

In an article for Business Insider, now-retired pro cyclist Andrew Talansky spoke glowingly about Halo Sport, claiming it had helped improve his efficiency on the bike.

“In your first effort [of a training session] if you’re doing five-minute intervals — even if it’s difficult and intense — you’re going to be pretty smooth and fluid,” said Talansky, who isn’t paid to use Halo Sport. “On the sixth one, maybe you’re going to be coming apart a bit. Halo has helped me improve staying efficient.

“There’s also the benefit of, you know, race day, but the biggest benefit to be gained is in a lot of the training leading up [to] that, the repeated use for targeted workouts.”

As Aron Hill explains, research does seem to suggest that greater efficiency of motion is possible through tDCS.

“When we train ourselves to perform a task, the more we train at it the better we get at it,” he said. “We fine-tune our motor activity and this is related to neuroplasticity — basically the brain’s ability to reorganise its connections within the brain. And the idea behind these devices is that in that window directly after, the brain is in a state of hyperplasticity. You’ve increased its ability to learn new things so if you train during that window you might get faster and better gains during that training.”

For Talansky, the improved efficiency offered by Halo Sport doesn’t necessarily translate to greater power output.

“There’s nothing where you’re like, ‘I did 20 more watts today,’” Talansky told Business Insider. “But you can look at a time trial and maybe in the last 10 minutes of a 30-minute time trial where you start to become unraveled, like at the Dauphiné or California, and you still feel very solid on the bike, very fluid, able to keep the cadence up.”

Ironman triathlete (and Halo Sport ambassador) Timothy O’Donnell, by contrast, does suggest Halo does help him push bigger power numbers.

“Training with Halo Sport has really helped me develop a better connection between my mind and my body,” he said. “And on the trainer it’s a perfect opportunity for me to use my Halo system to really focus on my cadence and my technique.

“I’ve been training with Halo for several months and I’ve already seen the benefits in both power output and efficiency.”

What the science says

Paid athlete testimonials aside, what does the science say about the efficacy of tDCS for cyclists? Does it actually work?

In a review of the scientific literature published earlier this year, Luca Angius and co suggested the following:

“To date, there are a limited number of studies, showing inconsistent results and often with flawed methodological design. Nevertheless, the balance of evidence suggests that tDCS might have a positive effect on exercise capacity.”

Looking specifically at cycling, a 2015 study led by AH Okano found that using tDCS prior to a step test led to an increased maximum power output of 4%. They also found reductions in “rated perceived exertion” (how hard the riders found the test) and heartrate when compared to a sham condition. Meanwhile, a study the same year from Angius and co found that tDCS did not lead to improvements in time-to-exhaustion nor reduce discomfort felt by study participants.

The authors of the 2017 review concluded: “Given the uncertain mechanisms and the inconsistency of outcomes of tDCS prior to exercise, the use of tDCS prior to/during exercise should be treated with some caution.”

Aron Hill echoes this sentiment, saying he’s sceptical of devices like Halo Sport because the research isn’t yet there to back their claims.

“Since about 2000 when these studies first started … there’s been several thousand studies looking at the effects of tDCS and one of the key things that we keep finding is this huge amount of variability,” he said. “It is definitely having some effect on the brain and it is certainly having some effect on performance. But for every study that you see that might say that you get a certain improvement in performance, there might be another study that comes out that says you don’t see anything, or that you may see the opposite.

“When you pool them all together it becomes a very incoherent picture and and I’m just worried that the science isn’t there yet to support [Halo’s] claims.”

This seems to be particularly true when it come to elite athletes. While several professionals that have used Halo Sport have been glad to promote the device, it’s even less clear that the device will be effective for those at the top of the sport, compared with those in the amateur ranks.

“A lot of this research has been done in just normal healthy people,” Hill said. “And I think if this is taken to the extent of elite athletes, it’s hard to know if those effects are going to actually compare because they’re people who are already performing well above average.

“I think [there’s] quite a chance that they may already have quite a bit of a ceiling effect where it may not make that much difference. But as far as I can tell the research just isn’t there really looking at that yet.”

Pro Ironman Timothy O’Donnell swears by Halo Sport, but the evidence isn’t there yet to suggest tDCS works for elite athletes.


The idea of sending an electric current into your brain, in an attempt to improve sports performance, is one that raises eyebrows for many people. Concerns about health and safety are, understandably, front of mind. So how safe is tDCS?

When administered in controlled, laboratory settings, and when using devices approved for scientific study, tDCS is considered very safe.

“Some of the adverse effects might be a mild headache or a bit of a sort of itching or tingling sensation directly under the electrodes when it’s delivered,” Hill explained. “But in terms of serious adverse effects, there really haven’t been any.”

But as Hill points out, things might be very different when devices like Halo Sport are being used at home, and used repeatedly.

“These devices are obviously not [used] in laboratory conditions — they’re being applied by people however they choose to apply them,” he said. “I think one of the key things when it comes to safety is in the lab we often apply this once or we might apply it for a week, but if people are going to be applying this every day for a long period of time, we have no idea what the effects are long-term.

“And I think that’s a really important issue because the effects that occur after one session may be very different to the effects that occur after using this device for six months.”

We put that concern to Dr. Chao.

“To say that there’s no data [about the long-term safety profile] is wrong,” Dr Chao said. “There’s some data. I would also agree with you that the vast majority of the data is in shorter-term studies. So that is something that we want to help change.

“The reason why most of the safety data — most of the efficacy data as well — is in shorter-term studies is really a matter of research convenience and practicality. It’s hard to bring these test subjects back over and over through weeks and months and even years.

“We’re building up our own dataset and [ours] can be a lot bigger than any researcher because our dataset grows by the day. For every additional device that we sell that’s another user and that’s another user account that we can track over time. I think we have over 75,000 stimulation sessions recorded. And many of those are from users that have used it over 100 times.

“So by reports, so far even with longer-term use, there’s no additional side-effects that we can detect. And then we also do sort-of blinded, sham-controlled, randomised studies that are reminiscent of a research university. So we have almost 2,000 people that we’ve enrolled in these types of studies and even when we go deliberately hunting for side-effects, we can’t find any side-effects that are greater than the control group.”

Aron Hill suggests treating Halo’s in-house studies with scepticism.

“Unless these are published scientific studies I wouldn’t take them too seriously,” he said. “I mean, obviously they’ve got a lot of vested interests — they’re trying to sell a product at the end of the day.”

The Halo Sport headset is paired with a smartphone app to deliver neuropriming sessions.

There’s another issue of concern with the long-term use of tDCS. In 2016, a group of 39 tDCS experts endorsed an article in the Annals of Neurology entitled “An Open Letter Concerning Do-It-Yourself Users of Transcranial Direct Current Stimulation”. Among the group’s concerns was the fact tDCS might have effects in the brain beyond what the manufacturers of devices like Halo Sport intend.

“The effects of tDCS can extend beyond brain regions directly affected by the stimulation to connected brain regions and networks,” the letter reads. “These indirect effects of stimulation on connected brain networks may alter brain functions that are unintended.”

That is, stimulating one area of the brain might improve the ability to perform one task, while simultaneously harming another.

“Such tradeoffs are likely under-recognized, as most tDCS studies focus on only one or two tasks,” the letter continues. “Furthermore, such cognitive trade-offs could develop over time and only become recognizable long after the stimulation.”

Dr. Chao acknowledges the possibility of unintended consequences.

“I think that’s a theoretical concern, but I haven’t seen any good published findings explaining this teeter-totter,” he said. “I guess that’s what Rachel [Wurzman, the letter’s lead author] was putting forth in this open letter: ‘OK, everything is zero-sum so if one goes up the other needs to go down.’ At the same point, and to maybe support this argument … I guess I wouldn’t be surprised if something were found.

“I think we understand this trade-off in life, that we can generally try to improve ourselves, but if we do improve ourselves in one area it could come at the expense of another area. So for example, going back to cycling, I can decide to be a really strong sprinter. But that is going to come at the expense of me being a really great climber.

“In the case of motor cortex neural stimulation for enhanced motor learning, I haven’t seen any trade-offs so far, unless it’s the typical sort of body-changing type of trade-off where you want to be bigger and stronger but less efficient on a climb. That could be a result of the way that you’ve been training but it’s more a function of the way that you’re training and less a function of the brain stimulation.”


Assuming tDCS does indeed improve sports performance, this raises the potential for ethical concerns. Could the use of Halo Sport and other devices conceivably be considered a form of doping? Would athletes that use this technology be getting an unfair edge? Dr. Chao doesn’t believe so.

“We sell the equipment to anybody,” he said. “So everybody has free access to it. Granted it’s not cheap — it’s $750 — but you know, for many of your [readers] that’s less than the front wheel. I’m not even including the back wheel because maybe the rear hub is $750.

“There is performance-enhancement all around us and [much] of it is legal. In fact most of it is. Like lifting weights is performance-enhancement, eating healthy is performance-enhancement — all of that is legal. So what makes it illegal is one: its safety. If it’s unsafe to the health of the athlete then that should be illegal. We can all get around that. And there’s this other concept of free performance — if you take something and just the mere fact that you took it, you get something for free? That is also problematic. EPO would fall into that category — you take a shot of EPO and you get free red blood cells.

“With Halo Sport you get nothing for free. If you were to use the neurostimulator sitting on the couch, drinking a beer you’re not going to get better at cycling.”

In conclusion

It’s clear from the science that tDCS stimulates the brain and that it has the potential to promote small improvements in some areas, for some people. But the science is far from settled, and there are questions to be answered about the long-term safety of the technique, and perhaps the ethical implications when it comes to competition.

But as the sport of cycling knows all too well, there will always be those that are willing to take a risk to improve their performance. As Dylan J. Edwards wrote in a 2017 paper, “In a society increasingly driven to succeed with less effort, performance enhancement with an intervention that has an excellent safety record, is well tolerated, relatively inexpensive and readily available, is particularly appealing.”

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