THURSDAY THINKER - What is Fatigue: When, on a blustery day in Oxford in 1954, Roger Bannister ran the first sub-four-minute mile, measuring out the full capacity of his lungs and legs and collapsing across the finish line, he felt, as he later wrote, “like an exploded flashlight.” That was the feeling researchers were trying to evoke, recently, when they paid thirteen volunteers at Bangor University, in Wales, to pedal a stationary bike at a predetermined pace for as long as they could. Such “time to exhaustion” trials are a well-established method of measuring the limits of physical endurance, but in this case the experiment also had a hidden psychological component. As the cyclists pedalled, a screen in front of them periodically flashed images of happy or sad faces in imperceptible sixteen-millisecond bursts, ten to twenty times shorter than a typical blink. The cyclists who were shown sad faces rode, on average, twenty-two minutes and twenty-two seconds. Those who were shown happy faces rode for three minutes longer and reported less of a sense of exertion. In a second experiment, the researchers demonstrated that subliminal action words (GO, LIVELY) could boost a subject’s cycling performance by seventeen per cent over inaction words (TOIL, SLEEP). According to one study, fatigue is “the inability of the contracting muscles to maintain the desired force.” But what causes it? Physiologists in the early twentieth century studied exhaustion by cutting off the hind legs of frogs and electrically stimulating the muscles over and over until they couldn’t contract anymore. In 1907, the Nobel Laureate Frederick Hopkins and one of his colleagues showed that the depleted frog muscles were bathed in lactic acid. Their experiment gave rise to an enduring—and incorrect—explanation for muscle failure; scientists now know that lactate, the form in which lactic acid occurs in the body, actually fuels muscular contraction rather than inhibiting it. Nevertheless, the view of fatigue as a mechanical breakdown has persisted. You max out your ability to pump oxygen, the acidity of your blood creeps up, and the neuromuscular signalling between your brain and your muscles gets weaker: one way or another, you hit a limit. Marcora believes that this limit is probably never truly reached—that fatigue is simply a balance between effort and motivation, and that the decision to stop is a conscious choice rather than a mechanical failure. This, he says, is why factors that alter a person’s perception or motivation (monetary rewards, for example) can affect performance, even without any change in muscle capacity. In the subliminal experiments, the cyclists’ heart rates and lactate levels rose at the same rate no matter which faces they saw, indicating that nothing had changed from the neck down. Considerations like heat, hydration, and muscle conditioning, Marcora says, “are not unreal things, but their effect is mediated by perception of effort.” In other words, they don’t force you to slow down, as happens with the failing frog muscles in the petri dish; they cause you to want to slow down—a semantic difference, perhaps, but a significant one when it comes to testing the outer margins of human capability. #thursdaythinker newyorker/tech/elements/what-is-fatigue?mbid=social_facebook
Posted on: Thu, 22 Jan 2015 07:00:00 +0000
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