You know it all too well: that awful moment when overworked lungs and leaden lower limbs combine to create an overbearing desire to S-L-O-W D-O-W-N.
When the burden of placing one foot in front of the other grows intensely with every limping stride and you reach the end of your run – prematurely or not – convinced that you don’t have another step in you. You are, to use the scientific parlance, knackered.
Given where these go-slow sensations manifest, it hardly comes as a surprise that research into improving endurance performance has been based primarily around the theory that fatigue comes as a result of the body – the muscles, lungs and heart – telling your brain it has reached its limit. But what if it’s the other way around?
Mind over muscle
Considering the importance of the mind in reaching peak athletic performance is nothing new. Though somewhat intangible, elite athletes have long exalted the merits of mental power in eking out a physical edge that can mean the difference between gold and also-ran.
Sir Roger Bannister, who knows a thing or two about pushing the performance envelope, even hinted beyond the notion of willpower: “It is the brain, not the heart or lungs, that is the critical organ.”
A growing number of scientists are now in agreement, and many have centered studies on the precise role of the brain when it comes to endurance performance and fatigue. Among the first was Tim Noakes, professor of exercise and sports at the University of Cape Town and author of Lore of Running (£19.99, Human Kinetics Europe). Based on his findings, he argues that it is the brain that limits our endurance efforts before the body gives out.
The VO2 max debate
“But what about VO2 max?” you may ask, quite possibly in snatched breaths, bent double by the side of a track. After all, scientists and coaches have been pushing us to our lung-bursting limits based on the theory that a lack of oxygen to the working muscles is what limits performance since Nobel Prize-winning British physiologist AV Hill presented the basis for the theory some 90 years ago. The idea that oxygen delivery to the muscles is the whole story is neat and logical to the point of appearing almost self-evident.
But it’s wrong, contends Noakes, who first challenged Hill’s model as far back as 1987. In research published in the journal Medicine & Science in Sports & Exercise, Noakes reanalysed Hill’s data and discovered that in coming to his conclusions, Hill’s studies hadn’t actually proven that runners had run out of oxygen.
So what is happening? Noakes’s own research-based theory on endurance performance is the ‘central governor’ model. When it comes to fatigue’s red stop light, he says, your brain isn’t merely receiving the information, it’s in control.
“Fatigue is just a sensation – it’s your brain telling your body it’s tired, not the other way round,” says Noakes. And how does the brain pull rank on your brawn? “It inhibits force output by reducing drive to the muscles,” says Noakes, which cuts the number of motor units that are activated during exercise. In other words, your brain tells your muscles it’s time to slow down, rather than your muscles telling your brain.
If this alternative theory of muscle fatigue is correct, the significance is huge. But first things first, is the research there to back it up? Studying the levels of electrical activity in working muscles does provide compelling evidence: theoretically, as muscle fibres tire, more should be recruited to pick up the slack.
However, in a study that required experienced cyclists to perform 1000m and 4000m sprints over the course of a 100K time trial, Noakes noted that electrical activity in the muscles actually dropped as fatigue set in – even during the sprints, when the cyclists were pedalling as fast as they could.
“They felt as though they’d reached their physical limits, but they were actually only using 30 per cent of their muscle fibres,” says Noakes.
Noakes isn’t on his own here, either. A recent University of Birmingham study revealed even more about the brain’s tendency to ring-fence our energy supplies. Athletes were asked to rinse their mouths with (not swallow) either a solution of water and a flavourless carbohydrate called maltodextrin, or a placebo. Those who had swished the carb-based solution improved their performance in intense bouts of exercise lasting an hour or so.
It appears that the brain can sense carbohydrates in the mouth, even tasteless ones, says Matt Bridge, a senior sports science lecturer at the university. “Your brain tells your body that carbohydrates are on the way. And with that message, muscles and nerves are prompted to work harder and longer.” Remember, the carbs were not actually consumed, so there was no actual fuel boost. It was, as they say, all in the mind.
So why, exactly, is our grey matter so keen to slow us down that it pulls one over on us? According to Noakes’s central governor model, our brains are constantly keeping an eye on the bigger picture – stopping us pushing past the point where we have the potential to do harm to muscles and/or other organs.
To guard against an internal catastrophe, “a control system in a small area of the brain constantly monitors signals sent from all over the body”, says Noakes. If it interprets the information as a threat, your brain produces feelings of discomfort and reduces electrical output to the muscles to keep you safe.”
That’s when those fairly convincing ‘I must stop right now’ messages start bouncing around inside your head. You may feel them as coming express mail from your searing quads and stabbing calves, but they’ve actually never ventured to the business end of your running machinery. In fact, “those messages are sent from the sub-conscious brain to the conscious brain”, says Noakes.
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