AT THE 2014 Berlin marathon, Kenya’s Dennis Kimetto beat everyone who has ever run the 42.2-kilometre race, blazing his way to a new world record time of 2:02.57. Shaving 26 seconds off the previous best was an extraordinary achievement, particularly for a man who only began training seriously in 2010. And yet Kimetto was 3 minutes off the 2-hour mark – the fabled barrier considered by many as the greatest challenge left in sport.
Sports scientists will give you a familiar list of what is required to break that barrier: as high an oxygen capacity as has ever been recorded, impeccable running economy, a pancake-flat course, perfect temperatures and top-notch pacemakers. But perhaps that is not the whole story.
Until recently, scientists concerned with the limits of human endurance performance tended to focus on the physiological – how the body functions, in other words – and the environmental. Over the past decade, however, they have come to understand that, to a greater extent than ever previously imagined, those limits are determined by the grey lump between your ears. The brain makes the call to slow up or break down long before the lungs and limbs are finished. Understand how, and not just elite athletes, but all of us could be on our way to cheating fatigue.
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In the world of exercise physiology, fatigue is the inability of muscles to maintain desired force. It has typically been viewed as a mechanical breakdown. You reach a limit in your ability to pump oxygen to muscles, lactic acid accumulates in the blood and you slow down or give up. Alternatively, you exhaust glycogen reserves in the muscles, meaning you can’t create sufficient energy to carry on.
That was perspective when in 1991 he published an influential paper in which he calculated the fastest possible marathon time. Joyner, who now runs a physiology lab at the Mayo Clinic in Rochester, Minnesota, took into account the physical attributes widely accepted as integral to endurance to arrive at a figure of 1:57.58. That is almost 5 minutes faster than today’s record.
Most efforts to close the gap still focus on the same physical characteristics. A year after Kimetto set the current marathon record, Yannis Pitsiladis, an exercise physiologist at Brighton University in the UK, floated a new project designed to break the 2-hour barrier in five years by bringing together experts in nutrition, physiology, biomechanics and race preparation – an ambitious goal given that in the past decade the record has dropped by just 3 minutes. The problem is, Pitsiladis’s venture appears to overlook the role of the brain.
The idea that our physical limits might be imposed by the mind is not entirely new. In the late 1990s, at the University of Cape Town in South Africa proposed that the brain holds the levers of a subconscious safety device that kicks in to prevent organ damage. This self-preservation mechanism, known as the “central governor”, seemed to explain why athletes running on hot days tended to start slower than on cool days: if the subconscious brain perceives a threat, it slows you down to prevent your core temperature rising to dangerous levels. Perhaps this self-preservation apparatus is what prevents Kimetto and others from going below 2 hours.
That is not how sees it. An exercise physiologist at the University of Kent, UK, Marcora agrees that the brain controls the body’s brakes, but he has a different take on how it makes the decision to apply them. He argues that fatigue depends primarily on the conscious brain and specifically how we perceive effort. As a result, he insists that even the greatest athletes quit or ease off not because their bodies can no longer go on, and not because the subconscious brain steps in to protect their organs, but because they think they have reached some maximum level of effort. At that point they make a conscious choice to stop.
The choice is yours
Anyone who has broken down long before the finish line would have something to say about that. But Marcora has produced evidence to support his theory.
In one study he recruited 10 men from Bangor University’s rugby team for a “trial to exhaustion”. He put them on exercise bikes and had them pedal at a fixed power output based on 90 per cent of their maximum aerobic capacity – on average 242 watts – until they could no longer maintain it. Then, as soon as the riders had given up, they were told to pedal as hard as possible for another 5 seconds. They produced an average of 731 watts – way above the output that had just driven them to exhaustion (European Journal of Applied Physiology, vol 109, p 763).
Marcora suggested that although the rugby players had suffered lactic acid build-up and glycogen depletion, such physiological effects had not directly stopped their muscles working. Rather, those effects had made the mental effort required to carry on harder and harder until the riders gave up. “When effort is perceived as maximal or when the effort required eclipses the amount of effort you’re willing to exert, then you stop,” says Marcora. Ultimately, then, endurance performance comes down to your conscious perception of how much you’ve put in.
Not everyone is convinced. , an exercise physiologist at the University of the Free State in Bloemfontein, South Africa, insists that Marcora’s study revealed nothing new. “It is one of many studies or reviews that have documented some kind of capacity to increase power output at the end of exercise, when a known finishing point is provided,” he wrote in response to the 2010 study. Most people who have pushed the limits of their endurance will have experienced this “second wind” at some stage, perhaps when the finishing line finally comes into view.
Noakes, meanwhile, argues that it is not realistic to conclude that the conscious perception of effort is the ultimate regulator of endurance performance. In his view it is too simplistic to think that we have complete control over when we call it a day.
For elite athletes and rank amateurs alike, how you train depends on who you believe. Noakes’s central governor model supports high-intensity training techniques such as interval and hill sprints, where you punctuate full-throttle workouts with short rest periods. The idea is to convince the brain that the body can delve into its reserves without damaging vital organs. Marcora’s conscious decision model, on the other hand, suggests a novel approach: if it all comes down to how the brain interprets signals about effort, perhaps the best approach is to change the way it interprets those signals.
To some extent that is what coaches get paid for. They psychologically prepare their athletes for the moment when motivation begins to yield to fatigue. Now, though, Marcora has begun testing “brain endurance training” methods designed to raise an athlete’s perception-of-effort threshold.
Last year, he asked 35 British soldiers to take a 60-minute cycle trial, during which he measured physiological limiters. Then he split the subjects into two groups. Both trained on an indoor bicycle three times a week for 12 weeks, but one group performed a mentally fatiguing task – picking out combinations of letters on a screen – as they pedalled.
“Deception seems to work even when the riders know they are being conned”
The results raised a few eyebrows. While the control group improved their time to exhaustion by 42 per cent, the brain-training group improved by 126 per cent. The latter group also reported finding the test less painful. “The results showed that the subjects could tolerate a harder perceived effort, so when the cognitive task was removed, the effort felt easier,” says Marcora.
There are important caveats. Studies like this are subject to placebo effects because it is difficult to properly “blind” subjects – the soldiers who did the brain training may have raised their levels because they knew that was predicted. But let’s say the results can be replicated, the question remains: how does this brain-training method work?
Marcora suspects that answers lie in the anterior cingulate cortex (ACC), a brain region that has been implicated in a variety of cognitive and emotional functions. His hypothesis is that if you systematically stress this brain region with cognitive tasks, you build up its resistance. His study seems to bear this out, though he admits it will need following up. “We did not measure brain adaptation, so there is no direct evidence of a training effect on the ACC yet,” he says.
He also proposes that monotonous mental tasks might lead to a build-up of adenosine, a brain chemical produced by neurons during prolonged activity. It accumulates when you are deprived of sleep, binding to adenosine receptors on cells in the brain and elsewhere. By slowing down the activity of those cells, it makes us feel mentally fatigued. That’s why caffeine, which blocks adenosine receptors on neurons, makes us feel awake.
Marcora suggests that consistently flooding the brain with adenosine by doing mundane mental tasks forces your brain cells to adapt, building resistance to this fatigue-inducing chemical. “Given that the ACC is likely to be intensely activated during prolonged exercise, the hypothesis is that adenosine builds up in this area, causing changes in perception of effort and self-control,” says Marcora. The result is that your sense of exertion goes down for the same level of actual effort.
Sadly you cannot become a world-class marathon runner by curling up with a copy of Puzzler magazine instead of putting in the hard yards. “If you have weaker muscles, you have to increase the activity of the brain to compensate,” says Marcora. “This is perceived as an increase in effort.” That means you will reach your effort threshold sooner than someone in better shape. Even so, if his theory is correct, you should make a point of exercising when feeling mentally drained – after an energy-sapping day at work, say, or a bad night’s sleep. You might find yourself cursing Marcora as your adenosine levels soar, but the idea is that you build up your resistance and, over time, keep that “I’ve had enough” feeling at bay for longer.
Marcora has caused a stir among endurance researchers, but he is not the only one convinced that manipulating the brain could bring performance gains – and his mundane on-screen tasks are not the only option.
In 2011, , now at the University of Canberra in Australia, had a group of cyclists undertake a 4-kilometre time trial at personal-best pace. He then had them race against an on-screen avatar that they thought was going at their best pace when really it was going 2 per cent faster. The riders kept up, cycling faster than they ever had before. But when the avatar was set to go 5 per cent faster, the riders couldn’t handle it. “That showed us the body has an energy reserve of 2 to 5 per cent,” says Thompson, and suggested that it can be tapped by tricking the brain.
The method seems to work even when the riders know they are being conned. Ren-Jay Shei at Indiana University in Bloomington worked with Thompson to replicate the study in 2014 and again the majority of riders beat their best by 2 per cent. When the researchers told the athletes they had been deceived and asked them to race the avatar one more time, they still managed to go 2 per cent faster than their personal best. “They’d shifted their pacing template,” says Thompson.
Electrifying pace
When Kimetto broke the world record in Berlin, he kept an average pace of just under 13 miles per hour – faster than you can go on most treadmills. It breaks down to an average of 4 minutes 41.5 seconds per mile. To go under 2 hours, that figure would have to drop by 6.5 seconds per mile. Thompson’s deception techniques could potentially help – if only marathons were run in the lab. The trouble is that such trickery is harder to pull off out there in the real world, not least because it would be hard to find human pacemakers up to the task.
What’s more, it is not yet clear if brain training or deception will work for elite athletes. After all, they are the elite because they have trained their minds to tap energy reserves that most of us can’t reach. Even so, some of the world’s leading elite endurance sports teams have begun to test a more direct way to alter perception of effort: zapping the brain with electricity.
The Red Bull High Performance team, for instance, is working with neuroscientists from Weill Cornell Medical College in New York City and Pepperdine University in Malibu, California, to see how its athletes respond to transcranial direct-current stimulation (tDCS), where a weak electrical current is applied to the brain. Team Sky, the all-conquering British cycling outfit, is also reported to be exploring the technique’s potential.
The trials build on work suggesting which brain regions it might be best to target. In 2011, a team led by at the University of Zurich in Switzerland measured the electrical activity in the brains of cyclists as they pedalled to exhaustion. As the subjects tired, Lutz noticed a steady increase in the intensity of communication between the motor cortex, which controls movement, and the insular cortex, which processes signals from the muscles and other components of the body. The results indicate that your insular cortex responds to signals of distress by ordering the motor cortex to give it a rest.
Based on this, at the Federal University of Rio Grande do Norte in Natal, Brazil, gave a group of cyclists a 10-minute bout of tDCS over the insular cortex. He found that they generated 4 per cent more power and reported lower perceived effort levels than before the brain zaps.
So can brain stimulation really help elite marathon runners shave 177 seconds off the record? Holden MacRae, a sports scientist at Pepperdine who led the Red Bull project, thinks so. “Potentially, manipulating the brain via tDCS could lead to that level of performance with the right athlete in optimal conditions and on a fast course,” he says. “Ethically, though, would tDCS be any different to performance enhancing drugs?” That is a debate for another day, even if that day might arrive sooner than you think.
But when you consider that Kimetto and others have chipped away at the marathon record for years with little or no scientific input, it does not seem so far-fetched to suggest that evidence-based brain manipulation could take them to new heights.
As for the rest of us, although we are unlikely to seek a course of brain stimulation to win the local fun run, this line of research promises to bring novel ways to tap hidden energy reserves. “Ultimately, the brain does regulate performance,” says MacRae. “Determining how to manipulate that regulation is the challenge.”
This article appeared in print under the headline “:Effortless:”
