The finishing kick is in your head, not your legs


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Another cool study showing that your brain always holds back a little energy even during “maximal” effort — and that you can access this reserve during your finishing kick. This one comes from Northumbria University in the UK, published in Medicine & Science in Sports & Exercise, and it’s fairly straightforward. Nine trained cyclists each do three 4,000-metre time trials on a stationary bike hooked up to pseudo-virtual-reality computer system:

  1. a baseline trial where they go as fast as they can;
  2. a “race” where they compete against an avatar representing their baseline performance;
  3. another “race” where they compete against an avatar which they’re told represents their baseline performance, but is actually going 2% faster (the second and third trials were given in random order to avoid learning effects).

The results: as you might expect, when racing against their previous performance, the cyclists were able to eke out a little extra energy, finishing 1.0% faster on average. But crucially, when they were deceived into competing against a faster avatar, they managed an even bigger boost, improving their time by 1.7%! Interestingly, an earlier study that tried something similar but gave feedback that was off by 5% produced the opposite result, because the cyclists were tricked into going out too fast and eventually crashed — so this isn’t an unlimited technique that will allow you to travel at the speed of light.

On the surface, these results aren’t really that surprising. Knowing how the human body (and mind) work, that’s pretty much what we’d expect. But it’s important to realize that this conflicts with the conventional understanding of how physiological constraints limit our performance. Whatever factors determined the baseline finishing times, they clearly weren’t absolute physiological limits, because the cyclists were able to beat them a few days later.

Further analysis of the data shows that in the deception trial, the cyclists had to start supplying more anaerobic power in the final 10 percent of the race in a desperate attempt to keep up with their supercharged rival. Here’s the graph of aerobic and anaerobic power contributions in the three trials (baseline, accurate and deception):

This graph sheds some interesting light on a longstanding debate about the origins of the “finishing kick,” which is a pretty much universal phenomenon in endurance races lasting longer than a few minutes. Why are we able to accelerate at the end, when we should be at our most tired? The conventional answer is that we’ve been relying primarily on aerobic energy throughout the race, but as the finish line approaches, we can mobilize anaerobic sources — the same ones we’d use to sprint 100 metres — and exhaust them just as we cross the line. The “alternate” explanation is that the brain has been limiting exertion in order to preserve homeostasis, but permits us to access some of those reserves as we approach the finish line (with the implicit promise that we’ll then stop and allow the body to recover).

It’s certainly true that the extra power needed for the finishing kick comes from anaerobic energy sources. But it’s also clear that, in the baseline trial and even in the “accurate” competition trial, the cyclists didn’t fully exhaust their anaerobic energy stores. Why not? The answer can lie only in the brain.

So what’s the practical takeaway? Well, I suppose if you can convince your real-life competitors to run 2% faster than normal without telling you, that would help! But realistically, I think this is a situation where knowledge is, literally, power. When you approach the finish of a race, you DO have energy remaining, despite what your mind and body are telling you. Believing that beyond a shadow of a doubt is, I believe, the first step to accessing it.

6 Replies to “The finishing kick is in your head, not your legs”

  1. In a Darwinian jungle, the idea of the body always saving a little energy, just in case something is lurking over you, even if it means the prey gets away, makes sense.

    Suppose you max out by over riding your own monitor, even if you catch the prey, you are rendered too weak to escape that which is hunting you at any moment. So, the animal that exhausts itself each time it catches dinner, over riding its monitor, will die out, getting eaten as much as it gets to eat. Well, maybe not as much, but if it maxes out every time, or even 1 out of 5 times, eventually, that one time, chomp, it is too tired to escape.

    Also, most animals have to defend the prey after they kill it. Gotta have some energy left to fight them off.

    Otherwise that species just becomes the hunter for the lazy guys who come in after you are too tired to defend your own dinner. Not to mention, once one animal is dead, its tends to attract even your own kind, thieves that they are, so you need some energy then too.

    Or even worse, there you are panting exhausted next to your dinner, and the remainder of your competitors, always lurking on the edge, watching, take that opportunity to breed with your mate, while you have just watch and recover. Ouch. That “over ride your monitor” gene trait would die out.

    There is never a moment in the wild when you can afford to be so tired you cant defend, or flee.

    Better to be hungry than dead.

    And what could be more annoying than maxing out to catch some rabbit and then have the dog next door just amble up and walk away with it cause you are too spent to fight him off, laughing at you the whole time?

    So, it seems that any species without a “reserve monitor” gene trait, would soon be someone’s dinner themselves, or lose theirs to the thieves and hyenas.

    Nowadays, we don’t have to save a bit, just in case something is lurking in the jungle, watching us hunt everyday, knowing that sometimes we max out and become easy prey. Or do we?

    Am I making sense? At least some? BTW, I love this site, very grateful it.

  2. Darwin:

    I think you miss the point slightly. It wasn’t about using absolutely all of your fuel, it was about whether you were using fuel at the fastest rate you could near the end of a marathon (not whether you were using it all up). So you might make your kill, and then the question then would be not whether you are so tired you can’t even move, but whether you can move faster or as fast. Also, you give sprinting examples which I think would be different than running a marathon.

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