Hourly two-minute exercise breaks nudged cognitive test scores in 1115 pooled participants

The two largest numbers in the review are subgroup estimates. Trials run in schools or workplaces came in at g = 0.61, about two and a half times the pooled figure. Trials where people kept the habit up for several weeks came in at 0.51, a little over double ^[7][19][21]. Those subgroups are sets of studies. No participant was randomised into a classroom or into a longer course of breaks, so the trials in each group differ from the rest in whatever else separates a school hallway from a laboratory. New Scientist's account of the review does not give the number of trials behind either figure ^[22].

Mark Hamer at University College London said the overall effect size is hard to interpret because the youngest and oldest people in the studies were at very different stages of cognitive development, though he thinks the findings are plausible ^[9]. The classroom case interests him most. "It's interesting with the kids in particular and this concept of trying to break up lessons, which could involve a teacher getting the kids to stand up or jump on the spot," he said ^[10].

Mike Trott at the University of Queensland, who was not involved in the work, said: "Exercise improves pretty much every domain you can think of, including cognition over the long term. The interesting thing here is that this is immediate" ^[11]. The leading hypothesis he describes is a release of dopamine and noradrenaline together with increased blood flow, linked over longer periods to a larger hippocampus and better prefrontal cortex performance ^[12][16]. He explains the spacing result by how long that response lasts. "The immediate effects of dopamine and noradrenaline last for over an hour, so if the exercise snacks are more frequent than that, any extra effect is going to be really small because you're still riding the wave of the first one," Trott said ^[13]. The review itself measured test scores.

The trials tested less than the standard definition allows. An exercise snack is generally defined as a session of up to 10 minutes done at least twice a day ^[15], and the trials used a couple of minutes at a time ^[3]. The World Health Organization's minimum is 150 minutes of moderate activity a week, or 75 minutes of vigorous activity, and about 31 per cent of adults do not reach it ^[14]. Spread evenly, 150 minutes a week is roughly 21 minutes a day, which at two minutes a break works out at about 11 breaks ^[20].

What the 0.24 covers is performance on tests of working memory, cognitive flexibility, attention span and the ability to ignore impulsive reactions, measured immediately after the movement ^[5]. A small gain on an attention task measures one thing; a lesson's worth of learning measures another. Hamer said current health messaging about breaking up the day rests mainly on cardiovascular and metabolic evidence ^[17], and that the cognitive work adds to the case for interrupting long sitting: "Even if that's just by standing up or going up and down the stairs" ^[18].