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Older adults who sweated through 12 weeks of high-intensity interval training improved their performance on a memory test by 30 per cent compared with those who did a more moderate exercise routine.Graham Oliver

To understand why a new study from researchers at McMaster University’s NeuroFitLab is making waves, it helps to look back at one of its previous findings.

In 2017, a team led by the lab’s director, Jennifer Heisz, published a five-year study of more than 1,600 adults older than 65 that concluded that genetics and exercise habits contribute roughly equally to the risk of eventually developing dementia. Only one of those two factors is under your control, so researchers around the world have been striving to pin down exactly what sort of workout routine will best nourish your neurons.

Heisz’s latest study, published last month in the journal Applied Physiology, Nutrition, and Metabolism, offers a tentative answer to this much-debated question. Older adults who sweated through 12 weeks of high-intensity interval training improved their performance on a memory test by 30 per cent compared with those who did a more moderate exercise routine.

But the real significance of the findings may have less to do with the specific details of the workout routine than with the fact that even subjects as old as 88 were able to stick with a challenging exercise routine and improve their memory. Because in the quest for brain health, as in the parallel quest for physical health, the real challenge is finding ways of making exercise accessible and sustainable.

The new study involved 64 sedentary adults older than 60 who were divided into three groups that each met three times a week for 12 weeks. Before and after the training period, their physical fitness and cognitive performance were assessed.

The interval group warmed up and then did four-minute bouts of hard treadmill walking at 90 per cent to 95 per cent of their maximum heart rate, repeated four times, with three minutes of easy walking for recovery. The moderate exercise group walked at 70 to 75 per cent of max heart rate for 47 minutes, which burned the same total number of calories as the interval group. The control group, meanwhile, did 30 minutes of relaxed stretching.

Perhaps the most worrying observation was that many people in the control group showed measurable declines in both physical fitness and memory. Staying active isn’t just about boosting your performance; it’s necessary just to keep what you’ve got.

And while the headline result was that the interval group did better, Heisz points out that previous work by her group and others has found that more moderate exercise can also help, albeit over a longer time frame. Adding intensity – “this can be as simple as adding hills to [a] daily walk or picking up the pace between light posts,” she says – just speeds things up.

In fact, when you zoom out to survey the larger body of literature in this area, the picture gets even murkier. Yes, both moderate and intense aerobic exercises such as walking or running seem to work. But so does resistance training, as do “gross motor skills” exercises that engage your brain as well as your body, such as yoga or ball games or simply walking in a rich and unpredictable outdoor environment rather than on a treadmill.

Louis Bherer, a researcher who studies exercise and brain health at the University of Montreal, points to a recent report by the Global Council on Brain Health, which concludes that there simply isn’t enough evidence yet to pinpoint a “best” form of exercise for warding off cognitive decline.

With that in mind, Bherer suggests aiming for a mix of different types of exercise – and, more important, finding something you enjoy. “The name of the game is to sustain it,” he says. “As soon as you stop, you start losing the benefits.”

In Heisz’s study, the most consistent feedback was how much subjects liked the social aspects of group training. The ingredients of an enjoyable exercise routine might be different for you, but figuring that out is probably more important than fretting over your heart rate zone.

“The positive message from this study,” Heisz says, “is that it is never too late to start.”

Alex Hutchinson is the author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.

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