Cure: A Journey into the Science of Mind Over Body
Page 9
He and Habeler set off from a camp at 26,200 feet early on the morning of May 8. As they neared the summit, their progress was increasingly slow. They were forced to climb ridges of rock, as trekking through the deep snow was too exhausting. Breathing was so strenuous that they scarcely had strength for anything else. It became harder and harder to stay on their feet, until eventually they had to collapse into the snow every few steps to rest before crawling on again. They knew that each foot they climbed might be the one that took them past a fatal boundary, the one that ensured they would never return. “I was attacked by a suffocating fear of death,” wrote Habeler later. “Now the lack of oxygen is beginning its deadly work.”1
Finally, between 1 and 2 p.m., the men saw a metal tripod left behind by Chinese surveyors in 1975. They had reached the summit. Habeler stammered and cried, his tears running from under his goggles into his beard and freezing on his cheeks. Messner says he just sat, legs dangling, with nothing to do at last but breathe: “I am nothing more than a single, narrow, gasping lung floating over the mists and the summits.”2
Messner and Habeler’s achievement was a supreme demonstration of endurance, despite bodies and brains that were screaming from lack of oxygen. Yet physiology experiments carried out since then on people exercising at high altitude have revealed a paradox.
It is well-known that people reach exhaustion more quickly at altitude. For example, aerobic performance in fit, acclimatized climbers is reduced by around a third at 17,400 feet compared to sea level. The traditional explanation is that in low oxygen conditions, our blood isn’t able to carry as much oxygen around the body. Our muscles become fatigued, and we are unable to continue exercising.
A 2009 study of climbers ascending Everest found that near the summit, at 27,600 feet, the oxygen content of their blood plummeted to just three quarters of normal levels.3 Messner and Habeler’s fear was warranted; if the mountain had been any higher, they may well have not survived. But surprisingly, in blood samples taken at all other altitudes, up to a dizzying 23,300 feet, the oxygen content of the climbers’ blood was just the same as recorded at sea level.4
In other words, below 23,300 feet, changes in blood oxygen content can’t explain climbers’ impaired performance at altitude. So what does? It’s possible that oxygen diffuses through the tissues less well in such circumstances, suggests study author Daniel Martin, director of the Center for Altitude, Space and Extreme Environment Medicine at University College London.5 So even though blood oxygen levels are maintained, less oxygen gets to the cells that need it. But other strange results hint that something else might be going on.
If climbers indeed get tired at altitude because their muscles run out of oxygen, then you’d expect that when exhaustion hits, their hearts should be pumping as fast as possible in an attempt to carry the maximum amount of oxygen around the body. You’d also expect to see particularly high levels in the blood of lactic acid—a toxic waste product that accumulates when the body is short of oxygen. Yet in study after study, scientists have seen neither of these things.6 People tire at altitude after relatively gentle exercise, even though their hearts still have plenty of reserve capacity. And as they climb higher, the level of lactic acid in their blood at the point of exhaustion actually falls.7
We fight for breath and struggle to exercise even when oxygen levels in our blood are maintained, with no sign of stress or damage to the brain, muscles or heart.
What is it, then, that slows us down?
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ON AUGUST 12, 2012, a 29-year-old Londoner named Mo Farah walked onto the track for arguably the biggest race of his life: the 5,000 meters final at the London Olympic Games. As he approached the starting line, the elated home crowd gave him a standing ovation. A week before, they had seen Farah make history when he won gold in the 10,000 meters. In an event dominated by the African nations of Ethiopia and Kenya, it was the first ever British Olympic win. Now they wanted him to do it again.
But while he had been a strong contender in that race, this was a different proposition. Farah was still recovering from the physical exertion of his victory a week before. And the 5,000 meters was a much greater challenge. He was only eleventh fastest in the world that year, and seven of the faster athletes were lined up next to him, including the quickest of all, the Ethiopian legend Dejen Gebremeskel, who was the favorite to win.
Fortunately for Farah, the 12.5-lap race got off to a slow start. He sat back for most of the race, then for the last kilometer fell in second behind Gebremeskel as the pace picked up. In the stands, among thousands of waving Union Jacks, were his step-daughter and his wife, Tania, heavily pregnant with twins.
Farah pushed to the front, then as the bell rang for the last lap, he opened his stride and slid away from the pack—his slim frame moving easily in white singlet and blue shorts, a gold chain bouncing around his neck. Then around the final bend came Gebremeskel, closing fast in green and yellow. It seemed inevitable that the favorite would take the lead, but Farah seemed buoyed by a wave of noise from the crowd. Teeth bared, arms pumping, he somehow pulled away from Gebremeskel and flew over the line first with a look of wide-eyed elation and disbelief.
Farah had run the last mile in four minutes, and his last lap in just 52.94 seconds. BBC commentator Steve Cram (a former Olympic runner himself) was overcome with emotion. “My words cannot do justice to how I feel,” he enthused. “Have you ever seen anything like that?”8 Farah dedicated the two gold medals to his unborn twins.
I was watching the race at home, heavily pregnant myself. Our living room and the whole country were lit up by Farah’s achievement. Britain had never won a long distance gold at the Olympics; now we had two. Farah became a national hero. “The crowd was inspiring,” he said afterwards. “If it wasn’t for them, I don’t think I would have dug in as deep.”9 There seemed no doubt that to win us that medal, Farah had used every scrap of energy, every last muscle fiber, every ounce of will.
So what struck me almost as much as Farah’s thrilling sprint finish was what he did right after crossing the finish line. Instead of falling to the ground in exhaustion, he started showing off to the crowd with a set of sprightly sit-ups. Then he bounced up again and jogged around the track towards the waiting photographers, arms bent up over his head in his trademark M.
It’s a phenomenon that we see often in athletics. World records are broken; sprint finishes won. Athletes apparently marshal every resource to push their bodies to the limit, yet as soon as they cross the finish line, they have the energy and muscle strength to bounce around a victory lap. It raises a similar question to that raised by the climbers on Mount Everest. Why, when it feels as if we’re at the breaking point, do we have so much left in reserve?
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TIM NOAKES, a sports physiologist at the University of Cape Town, South Africa, is not the type to bow to authority. In fact, he makes a habit of overturning dogmas—sometimes making enemies but also saving athletes’ lives.
In the 1980s, for example, he carried out studies that revealed an epidemic of catastrophic neck injuries among rugby players in South Africa.10 His results were hotly denied at the time but ultimately led to a change in the rules. Then he investigated why so many marathon runners were collapsing. He concluded that it wasn’t because of dehydration, as everyone thought, but the reverse: they were drinking too much. According to Noakes, the official advice to runners—that they should drink around 50 ounces an hour—was poisoning them.
U.S. experts, influenced by the sports drink industry, rejected his findings. The advice wasn’t changed until 13% of participants in the 2002 Boston Marathon suffered water intoxication—and one runner died as a result. “My clash with the multibillion-dollar-a-year U.S. sports drink industry taught me that medical science can as easily be bent to serve commercial interest as it can be used to produce ‘the greatest benefit to humankind,’ ” Noakes said.11
Perhaps it’s not surprising, then, that Noakes has also spent years attacki
ng one of physiology’s most basic assumptions. As an athlete himself, he was interested in fatigue. “If you are exercising, you are always getting tired and trying to understand why,” he tells me. “I realized quickly that it wasn’t what we were taught.”12
The dogma was that athletes get tired when their bodies hit physical limits—their muscles run out of oxygen or fuel, or become damaged by the accumulation of toxic by-products such as lactic acid. This in turn triggers pain and fatigue, forcing us to stop exercising until we recover.
This basic theory had never been questioned since it was proposed by Nobel Prize–winning physiologist Archibald Hill in 1923. Yet when Noakes tried to test it, his results didn’t make sense. First, Hill’s theory predicted that if athletes exercise to their limit, then shortly before they stop with exhaustion, oxygen use should level off, because the heart can’t pump fast enough to get any more oxygen to the tissues that need it. But just as with the experiments at high altitude, that didn’t happen. “We couldn’t find that athletes were running out of oxygen when we tested them,” he says. “We couldn’t see it.”
Meanwhile other studies have shown that although levels of fuel inside muscles (glycogen, fat, ATP) diminish with exercise, they never run out. Noakes also studied muscle use, by asking cyclists to ride exercise bikes with wires attached to their legs. Hill’s theory says that athletes should recruit all available resources as they tire, engaging more and more muscle fibers until, with nothing more to give, they finally hit the breaking point. But Noakes found the reverse. As the cyclists neared exhaustion, muscle fibers were being switched off.13 At the point at which his volunteers said they felt too fatigued to continue, they were never activating more than about 50% of their available muscle fibers. Exhaustion forced them to stop exercising, yet they had a large reserve of muscle just waiting to be used.
All of this convinced Noakes that the old idea—of fatigue being caused by muscles pushed to the limit—couldn’t be true. Instead, he and his colleague, Alan St. Clair Gibson, proposed that the feeling of fatigue is imposed centrally, by the brain. Obviously there is a physical limit to what the body can achieve. But rather than responding directly to tired muscles, Noakes and St. Clair Gibson proposed that the brain acts in advance of this limit, making us feel tired and forcing us to stop exercising well before any peripheral signs of damage occur. In other words, fatigue isn’t a physical event but a sensation or emotion, invented by the brain to prevent catastrophic harm. They called the brain system that does this the “central governor.”14
From an evolutionary point of view, such a system makes perfect sense. Relying on signs of damage in the muscles to alert us to fatigue would put us perilously close to collapse every time we exert ourselves. Shutting down physical activity in advance ensures a safe margin of error, and means we can continue to function even after an exhausting challenge. “We say that’s the way humans evolved, because you always need energy afterwards to do other things,” says Noakes. We might suddenly need to run from a predator, for example. “And when we were hunting, we always had to take the food home.” This is why Farah, even though he ran his heart out to win that second gold, still had energy left for sit-ups and jogging the moment he crossed the finish line.
At altitude, Noakes argues, the effect is even more pronounced. The central governor detects the reduced oxygen in the air and calculates that physical activity in such conditions isn’t safe. Even though our muscles are fresh and perfectly capable of exercise, it causes us to feel so fatigued that we can barely walk, and instead diverts our resources to breathing, to make sure that the brain gets enough oxygen. The same thing happens in other potentially threatening environments too. We feel sluggish in hot weather not because our muscles are worn out but because the central governor limits our physical activity in case we overheat. When we are sick, signals from the immune system induce fatigue so that we rest and save our resources to fight the infection.
When Noakes first set out his theory of the central governor a decade or so ago, the notion that the brain—not the heart, lungs or muscles—might ultimately determine the limits of physical performance was seen as ridiculous. Today there’s still controversy over his ideas; for example, Everest researcher Martin says that although Noakes “may well be right” that the central governor, not lack of oxygen, makes us tire so quickly at altitude, this hypothesis is “not substantiated by any evidence.”15
But although exercise physiologists tend to be cautious, psychologists are increasingly convinced that the brain does play an important role in fatigue. For example, many performance-enhancing drugs, such as amphetamines, modafinil and caffeine, work by influencing the central nervous system, not the muscles themselves.16 Scientists have also stimulated the brain directly with an electric current to boost cyclists’ peak power output, and make them feel less tired.17 Noakes says he hopes that over the next few years, brain-imaging studies will help to prove the existence of the central governor directly.
What intrigues me most about the idea that fatigue is controlled by the brain, however, is whether there is any role for the conscious mind. Can we, in effect, control the central governor?
There’s increasing evidence that sometimes we can. A raft of studies have shown that psychological factors can shift our perception of fatigue, adjusting the point at which we feel tired. Athletic performance is influenced, for example, by our motivation (from monetary reward or the presence of other competitors to the sound of gunshots), whether we are winning or losing, and how far we think we will have to run.
Meanwhile, psychologist Chris Beedie at Aberystwyth University in Wales has found that elite cyclists given a pill or drink that they believe is a performance enhancer can cycle on average 2–3% faster18—easily enough, in many events, to make the difference between winning a gold medal and failing to place. Beedie suggests this is because the placebo increases their optimism and self-belief, persuading the central governor to free up more resources. “The brain can do remarkable things but it also limits you,” he says.19 Taking a placebo lifts those self-imposed constraints. (Placebo expert Fabrizio Benedetti is also a fan of Noakes’s ideas, concluding in a paper on fatigue that “a placebo may act as a cue signaling the central governor to inhibit its brake.”)20
So in addition to physical variables such as temperature, oxygen availability, fitness and exertion level, the brain integrates psychological variables such as how confident we are, or how urgent the task is. It then uses the sensation of fatigue to set our maximum pace. If we are anxious about our state of fitness, or uncertain about how far we will need to go, we run slower. But if we are sure about the task ahead, or if we face a life-or-death situation, the governor takes that into account and loosens its grip.
This is why people are capable of feats of physical strength and endurance in emergencies that they would normally find impossible. And if the situation changes, our fatigue level changes too. During a race, we get a sudden boost of energy when we see the finish line. If we’re under threat, we feel exhausted as soon as the danger is gone.
When Farah readied for the 5,000 meters, his motivation, confidence and crowd support probably all worked together, persuading his central governor to allow an optimum performance and giving him the edge over his competitors. Meanwhile Messner and Habeler’s absolute determination to succeed seems to have pushed them dangerously close to the body’s absolute physical limits—to a record-breaking altitude that almost killed them.
The presence of the central governor may explain why interval training—short bursts of high intensity exercise interspersed by recovery periods—works so well. According to Noakes, regular sprints that push us close to our limit of maximum performance don’t just increase physical fitness, they also retrain the brain. They teach the central governor that pushing ourselves that hard was fine, so next time it’s safe to push ourselves a little bit further.
But perhaps it is liberating simply to know how over-protective the brain can be. “You don
’t have to believe what you are feeling and you don’t have to believe what your brain is saying,” says Noakes. “However bad you feel, you can carry on and you can still do better.”
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“IT WAS like being buried alive.” Samantha Miller tells me this matter-of-factly, fixing me with blue eyes as she munches on falafel. “I was exhausted, with terrible joint pains. It was like having flu all the time with no certainty of recovery. I couldn’t do anything. I was trapped.”
Today, Samantha looks vibrant, and younger than her 46 years. She is immaculately dressed in 1950s-inspired floral pinks with a fluffy beret and bright lipstick; her blond hair is twisted prettily and fixed with a white carnation. We’ve met for lunch in a Turkish restaurant on London’s fashionable Upper Street, and as we talk, she seems energetic, fun and very sharp. It’s hard to believe that she has just spent several years fighting her way back from hell on earth.
In the late 1990s, Samantha was living in Hampstead, London, and teaching art at a “short-staffed, under-funded” secondary school. She found dealing with kids tiring. Children still have “the invincibility of youth,” she says. “They haven’t been crushed by anything yet.” Samantha was also a keen mountain biker and swimmer, and led a hectic social life. If something needed doing, she would pick up the slack. And she was always striving to be perfect.
Then she got ill. “I had a glandular, viral thing,” she says. It didn’t occur to her to take time off from work. “So I was going in with a raging temperature. That was the point at which something changed.” Although she recovered from the illness, afterwards she felt sleepy all the time. A few years later she underwent a back operation, and while she was in the hospital, she contracted gastroenteritis. “It was horrific,” she says. “I was being physically assaulted from all sides.”