You're not that tired

A few years ago, good friends of mine dragged me to a viewing of Touching the Void, a movie about the extraordinary survival of a mountain climber against all odds. I remember coming out of that movie thinking, “Wow, when I complain that I’m tired, I’m really not that tired – I have so much more in me”. It might sound corny, but over the years, I’ve thought about this movie several times, and it has inspired me in many ways.

Which part of your body decides when you can and can’t go on? In exercise science, the debate has been going on for years. Some researchers think it’s the heart – you can only exert your big muscle so much. Others link stamina and endurance to lung capacity – measures like VO2 max (how much oxygen your body transports and uses during exercise) have been linked to performance in sports. More recently, measures like the lactate threshold (the exercise intensity at which lactic acid starts to accumulate in your blood) have become popular. Professional athletes are poked and prodded to try to figure out what makes a winner, but somehow with each theory comes at least one or two outliers. 

In an effort to investigate what drives people to push themselves and what sets the limits, British researchers came up with an interesting experiment using cyclists.

Each cyclist in their study had to complete four trials of 4 kilometers on a stationary bicycle. The first trial was just to get used to the equipment and the setting. The second trial was the real deal – they had to go as fast as possible, and their time was stored and used as the “baseline” time, or their “personal best”. During the last two trials, the participants “raced” against themselves – an avatar representing them was projected onto a big screen in front of them, and they could track their progress in relation to that of their avatar. The idea is that the avatar on the screen was going at the same speed as the cyclist’s 2^nd trial (the one used to set their personal best). The researchers were hoping to learn whether a cyclist could beat their trial time by chasing themselves to the finish line, thus establishing a new best time.

You can probably guess the outcome of the study: all the participants beat their best time when they raced against it. But there’s a twist: in one of the last two trials, the researchers tricked the cyclists: the avatar was actually going 2% faster than their previously established personal best. And every participant beat that time, too! So guess what? It’s not in your heart, or your lungs, or you legs. It’s all in... your brain.

What the study tells us is that you have a little energy reserve, even when you think you’re going all out. Your brain doesn’t want you to tap that reserve, because if you get into that habit, you might use it up and die. So it keeps it hidden. It makes you feel like you’re going to die even though you’re not. But the reserve is available – throw in a little deception and a little competitiveness (or, in the case of the mountain climber, a little actual fear for your life), and you can gain access to it.

So there you have it! Next time you didn’t sleep well and you’ve been going all day at work and running errands and working out and you just feel like collapsing on the couch and having a nap… Dr. Julie says… Collapse on the couch and have a nap. But do it knowing you could also clean the house if you really wanted to.

Reference: Effects of deception on exercise performance: implications for determinants of fatigue in humans. Stone MR et al. (2012) Med Sci Sports Exerc. 44(3):534-41.