The Frontal Cortex

Mental Exhaustion

Evan Lerner has a quite interesting article on about physical performance and exhaustion. That painful lactic acid throb? It’s mostly in your head:

The finish line is in sight, but you’re not going to make it. Your lungs are burning and deeply in oxygen debt. The muscle fibers in your legs have converted most of the carbohydrate supply in your body into lactic acid. This was a fine plan for generating the extra energy needed to keep you moving in the absence of adequate oxygen, but it is now making your quads and hamstrings feel like they are on fire – which is more or less the case. In short, your fuel tank is empty and you’re running on fumes. You are not going anywhere, except possibly to the ground in a heap.

The above scenario sounds totally plausible but is almost totally wrong. Runners are often at their fastest at the end of a race, when they should be the most tired. And, according to a new study, we can push ourselves harder when we expect to get a boost of energy from sugar, but long before those carbohydrates are actually absorbed. The experiment is clear evidence that our physical limits are less in our muscles and more in our minds.

The idea that muscle fatigue involves more than a lack of chemical energy is in some ways self-evident. Athletes perform better after consuming a sugar-laden energy drink, though the amount of energy contained therein is tiny compared to the reserves in their muscles. And according to a paper published earlier this month in The Journal of Physiology, athletes don’t even have to swallow those sugary drinks to feel a boost. The study – led by Ed Chambers, Matt Bridge, and David Jones at the University of Birmingham – cuts to the core of why we get tired at all.

This reminds me of a clever experiment led by Baba Shiv, of Stanford. (I describe this experiment in How We Decide.) He supplied a group of people with Sobe Adrenaline Rush, an “energy” drink that was supposed to make them feel more alert and energetic. (The drink contained a potent brew of sugar and caffeine which, the bottle promised, would impart “superior functionality”). Some participants paid full price for the drinks, while others were offered a discount. The participants were then asked to solve a series of word puzzles. Shiv found that people who paid discounted prices consistently solved about thirty percent fewer puzzles than the people who paid full price for the drinks. The subjects were convinced that the stuff on sale was much less potent, even though all the drinks were identical.

Why did the cheaper energy drink prove less effective? According to Shiv, consumers typically suffer from a version of the placebo effect. Since we expect cheaper goods to be less effective, they generally are less effective, even if they are identical to more expensive products. This is why brand-name aspirin works better than generic aspirin, or why Coke tastes better than cheaper colas, even if most consumers can’t tell the difference in blind taste tests.

I imagine a similar effect may be at work with athletes and physical exhaustion. The athletes who are convinced they’re in better shape are the ones that are mentally prepared to sprint towards the finish line. It’s a little easier for them to fight through the pain and persist, just like subjects given the non-discounted energy drink. Meanwhile, competitors who feel outmatched, or are maybe recovering from a nagging injury, might find these last-minute heroics to be a bit more challenging. In other words, everybody feels the pain – the real question is what we do with it.


  1. #1 Burt
    May 1, 2009

    Everything is in our minds – that’s why the placebo effect exists.

  2. Here we have an example of mobilising the very last pieces of energy to achieve goal just-in-sight even if you arecompletely exhaused. On the other hand I’m sure you know that children are able to show symptoms of sickness before going to shool, just out of fear. The same with placebo – if we strongly want some pill to work – it will, or more precisely – our body’ll respond in the way, we want it to.
    I believe that that all (I mean our bodies’ reactions) depends on our will and motivation. And as long as we know this it would be good to focus on those areas as well.

  3. #3 Niklas
    May 1, 2009

    I’m not sure i agree with the placebo-theory in this case. I guess it’s valid on some level but the article seemed to claim that the actual sensation of fatigue in the muscles went down after rinsing with sugary water. The effect seems, to me, to occur beneath, and without regard to cognition (the part of your brain that reads “sugar” on the bottle).
    The controls who rinsed with calorie-free water didn’t get a boost, so you’d have to propose some sort of unconcious placebo effect, which i find pretty bizzare.

  4. #4 doug l
    May 1, 2009

    Pretty interesting. The reference to lactic acid throb has been shown to be invalid, but the idea persists even among those who are reporting on human physiology.

  5. #5 Burt
    May 1, 2009


    The placebo effect IS unconscious – the conscious mind tricks the unconscious mind into believing a beneficial result is on the way and the unconscious makes good on the belief. Efficacy is proportional to the strength of conscious belief in the placebo.

  6. #6 Niklas
    May 2, 2009

    I understand, but that doesn’t hold in this case.
    The athlete is not conciously aware if there are any calories in his drink or not. The concious mind does not have access to that information. And since there is no conscious belief, there can be no conscious expectation and thus no placebo effect.

  7. #7 Christine
    May 4, 2009

    The mental component in overcoming the pain of lactic acid accumulation has been addressed in the athlete world. They call it, “lactic acid tolerance”. The better athletes have a better attitude towards the pain and therefore are less affected by it. They address that in training and help the athletes work through this kind of thing.

  8. #9 Matthew Putman
    May 6, 2009

    I recently saw the new Mike Tyson Documentary, which showed and reminded me of those early fights of Tyson. He knocked out amazing fighters in the early first round. Everyone in the world knew he was the strongest and fastest fighter. The point the film makes, and one that is obvious when looking at the faces of the soon to be defeated opponents, is that they were already defeated before the fight even began. There was a double mental advantage for Tyson. He believed completely that he was going to win, and the opponent believed also Tyson would win. This I think is another example of that athletic mental power, over pure physical reality.

  9. #10 Sand castings
    May 10, 2009

    Pretty interesting.

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