Different workouts have different short-term effects. If you want to feel the stress of a busy day gradually disappear, go on a relaxed trail run. If you've been dragging and want to jumpstart your central nervous system, sprint up a steep hill a few times. And if you want to be a little sharper for an afternoon meeting, do a moderate 20-minute aerobic session, suggests new research out of Taiwan.
The research looked at how people did on a cognitive ability test after each of three workouts: 10-minute cycle at moderate intensity, 20-minute cycle at moderate intensity and 45-minute cycle at moderate intensity, with each of the rides preceded by a 5-minute warm-up and followed by a 5-minute cooldown. The participants' scores on the cognitive ability test were compared to their performance on the test when they hadn't exercised.
The cognitive ability task was what's known as a Stroop test. In it, words representing colors are presented, and the test taker is required to say what color the word is printed in, regardless of what color the word represents. For example, if the word "green" is presented in red ink, the correct answer is "red." The Stroop effect describes the phenomenon in which it takes longer or is harder to give the right answer when the word is printed in a different color than the color it names (as in the example above) than when the word and the color it's printed in are the same (for example, if "green" were printed in green ink).
When the participants did the Stroop test after their 20-minute ride, they scored significantly better than when they'd taken it without working out first. The 10-minute and 45-minute workouts, however, had negligible effect on their test performance, as measured by accuracy and speed of response.
The researchers speculated that a 10-minute workout doesn't produce the short-term brain changes of a 20-minute workout, while, for the participants in this study, a 45-minute workout was draining enough to negate the benefits. It's likely that fitter people would see a cognitive boost from a longer workout, they wrote, but cautioned, "It should
be noted that after prolonged exercise (i.e., two hours), even participants with high fitness would be expected to experience decreases in cognitive performance, possibly due to central fatigue associated with heat stress, dehydration or hypoglycemia or to negative effects on information processing."
The workouts in this study were done at moderate intensity, about the effort level you'd keep on a steady, conversational run. Want to see if the study's finding applies to you? Take the Stroop test, enjoy a moderate 20-minute run and then try the test again.