You’ve got a big test or an important meeting coming up, and you want to be at your sharpest. You’ve heard over and over that even a single bout of exercise can heighten your cognitive abilities. So what exercise, exactly, should you do before the test? There are lots of variables to think about – type of exercise, intensity, timing, and so on. A new study in Medicine & Science in Sports & Exercise, from researchers at National Taiwan Sport University, takes a look at one of those variables: how long you should exercise.
The cognitive test they used was the Stroop task, where you have to identify the colour of colour words flashing on the screen. E.g. sometimes the word “green” flashes in green letters, and sometimes the word “green” flashes in letters of another colour. Sorting out the difference requires you to engage your executive control, an important cognitive skill. The exercise they used was moderate-intensity cycling (at 65% of heart-rate reserve), for either 10, 20, or 45 minutes. They also included a 5-minute warm-up before the exercise, and a 5-minute cool-down afterwards. Five minutes after the exercise finished, they completed the cognitive task.
The results were a pronounced dose-response relationship, with the best results at 20 minutes (which, including the warm-up and cool-down, is really 30 minutes of exercise).
As for the accuracy of the responses, the 45-minute session (55 including warm-up and cool-down) actually produced worse accuracy than the control condition, where participants just sat and read instead of exercising.
So the message seems to be pretty clear: about half an hour of moderate exercise optimises cognitive performance, and more than that may hurt it.
Now, there are a few questions that this study isn’t able to answer. For example, the volunteers in this study were healthy university students, but not necessarily fit. Would the same relationship hold with, say, habitual runners or cyclists? Even though intensity was normalised using heart-rate reserve, it’s not hard to imagine that 55 minutes of exercise would be much more fatiguing for someone who doesn’t exercise regularly than for someone who runs for an hour every day. But that’s a question for another study to answer.