Regular exercise and your focus

The nine trials were small - between about 30 and 70 students each - and seven of the nine were run in China, with one each in Spain and Germany. Everyone was a generally healthy university student, with average ages between about 18 and 23, so this says nothing direct about older adults, children or people with attention problems. Focus was measured with short attention tests, such as naming the ink colour of a printed word instead of reading the word, not with grades or real-world work. The result leaned on that colour-word test: on a second test, ignoring arrows placed around a target arrow, the difference was smaller and not clear on its own. The review also combined the trials with a method that assumes they share one true effect, which gives a narrower range than the alternative. Students knew whether they were exercising, and the comparison groups did nothing in its place. Across the whole review, only three trials reported keeping the group allocation hidden, four reported blinding the people who ran the tests, and two reported analysing everyone they had randomised. The review gave no overall rating of how certain the evidence is, and with fewer than ten trials it could not test whether small negative studies went unpublished. The programmes differed - running, Tai Chi, interval training, jump training and, in one trial, weight training - and the review does not report how long any benefit lasted after a programme ended.

This rests on seven small trials of healthy university students, most of them in China, and on short memory tests rather than on schoolwork or job performance. The students knew which group they were in, the review gave no overall rating of how certain the evidence is, and with fewer than ten trials it could not check whether unpublished studies would change the result. In the review's exploratory breakdown by type of exercise, the one Tai Chi trial did not show a clear benefit for working memory, while the aerobic, interval, jump and weight-training programmes did; several of those groups rest on a single trial.

The eight trials disagreed with each other more than chance would explain, and they used different switching tests, some of which moved and some of which did not. A result that is not clear is not proof of no effect; it means these trials could not show one.