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Now that Canada’s all-too-brief beach season has drawn to a close once again, you may be tempted to push the dumbbells to the back of the closet – to forsake vanity, forget bulging muscles and focus instead on the whole-body aerobic fitness that’s so tightly linked to health and longevity.

But a recent study from researchers at McGill University, published in the journal JAMA Network Open, offers a new reason for continuing to work on building muscle: It’s good for your brain, not just your biceps. Greater muscle mass, the results suggest, helps ward off cognitive decline in older adults beyond what you’d expect based on their exercise levels alone.

Want strong muscles? Eat your leafy greens

The findings are drawn from more than 8,000 older adults in the Canadian Longitudinal Study on Aging, with an average age of 73. They underwent a series of baseline assessments that included an X-ray measurement of their muscle mass, a battery of 10 cognitive tests and questionnaires about their exercise habits and other health characteristics. The cognitive tests were repeated three years later.

At baseline, roughly a fifth of the subjects met predefined criteria for low muscle mass. Over the next three years, compared with those with normal muscle mass, these subjects had a sharper decline in reaction times and in executive function, the cognitive skills that enable you to plan, focus attention, and prioritize your actions.

On the surface, these results aren’t surprising. After all, points out Stéphanie Chevalier, a professor at McGill’s School of Human Nutrition and the study’s senior author, previous studies have found that low strength and lack of physical activity predict more rapid cognitive decline. But there’s a difference between using muscle and simply having it.

Does muscle mass impact cognitive health?

“The question we asked in our study is: When we account for strength and physical activity, does muscle mass have an independent predicting role on cognitive decline?” Dr. Chevalier explains.

Using statistical techniques, the researchers were able to compare subjects with equivalent muscle strength, as assessed with a handgrip test, and equivalent exercise habits. Sure enough, those with lower muscle mass still had a faster subsequent decline in executive function, suggesting that muscle tissue itself has some sort of neuroprotective function.

Teasing out exactly how muscle helps the brain remains a challenge. There are plenty of indirect links: Those with more muscle are generally more active, which may help maintain the flow of oxygen-rich blood to the brain, for example.

But Dr. Chevalier’s results suggest there may be more direct mechanisms too. One possibility is the role of myokines, a set of hormone-like molecules produced by muscle cells that can travel to the brain and influence mood, learning and other cognitive functions. Greater muscle mass may also help keep blood glucose levels in check, protecting the brain from damage.

That’s not to suggest that strength training is the only path to better brain health. A 2014 study that followed 150,000 walkers and runners over a 17-year period found that meeting the standard recommendation of 150 minutes of moderate aerobic exercise a week was associated with a 25-per-cent reduction in the likelihood of developing Alzheimer’s disease. And those who got twice that much exercise had a 40-per-cent risk reduction.

Cardio or weights?

So if you want to cover all your bases, the choice between cardio and weights is easy: Do both. Incorporate some resistance training into your routine a few times a week. You don’t necessarily need to lift heavy weights, but push hard enough that your effort reaches at least eight out of 10 at the end of each set.

In addition, Dr. Chevalier adds, ensure that you have a good diet with sufficient protein, ideally spread throughout the day rather than concentrated into one massive protein bomb at dinner. There’s evidence that older adults become less responsive to the muscle-building stimulus of protein, so aim for about 0.4 grams of protein per kilogram of body weight with each meal. For someone who weighs 150 pounds, that works out to 27 grams of protein, the equivalent of a tuna sandwich, a glass of milk and a handful of almonds.

The bottom line

And remember, the goal still isn’t to wow everyone at the beach next year. A more realistic target for older adults is to keep the muscle you’ve got and prevent further losses, Dr. Chevalier says, citing the one ironclad law of exercise that no one disputes: “Use it or lose it.”

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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