Age-related brain changes linked to declining exercise habits after 49, research suggests

It’s well-established that as we age, we tend to be less active. Conventional wisdom points to loss of muscle mass, strength and issues of mobility as reasons physical activity declines later in life.

But Northeastern University researchers say the reason could also be linked to changes in the brain that occur around the time exercise starts to drop off for most people.

“We found that the brain can kind of predict some variance in people’s physical activity behaviors,” says Timothy Morris, an assistant professor of physical therapy, human movement and rehabilitation sciences, and co-author of the study.

In a study published in the Journal of Gerontology, researchers analyzed data previously gathered by the Cambridge Centre for Ageing and Neuroscience. Specifically, they analyzed a population-based cohort study involving participants between the ages of 18 and 81 that involved self-reported exercise data as well as magnetic resonance imaging of participants’ brains.

Researchers used a statistical technique called piecewise regression to isolate the point at which the association between age and physical activity diverges, which they noted was around the age of 49. They then turned to the brain to look for signs of neural mechanisms that might help explain the drop-off.

The study provides a look at the correlation between changes in key brain regions seen on images of participants’ brains and the decline in physical activity.

“There are going to be a lot of factors—social, environmental, economic, familial—that predict people’s physical activity engagement,” Morris says.

In recent years, researchers have been particularly interested in the role executive functioning plays in decisions to stay active. That’s a person’s capacity to focus on, plan and carry out goals, which includes cognitive processes such as multitasking, working memory and self-control.

“We’re now starting to see a convergence across different research groups that looks at precisely what in the brain is predicting physical activity engagement,” he says.

Much of that research has honed in on the role of the “salience network,” a set of structures in the brain that help us orient ourselves to certain stimuli in the environment. Involving such regions as the insula and the dorsal anterior cingulate cortex, the salience network could be thought of as the mind’s personal moderator, constantly on the lookout for objects in the environment—and responding to them in turn.

“Part of that network is another subnetwork that is related to inhibitory control, our ability to control these habitual, unconscious impulses called prepotent responses,” Morris says.

Morris explains, “Let’s say a person has the intention to go to the gym. You come home, you pick up your bag and you see the sofa in the room. We have this desire to minimize our effort as humans. Now, because you’ve seen the couch, you have to inhibit that desire to sit on it to go and be physically active.”

The theory goes something like this: aging leads to changes in the salience network, and changes in the salience network lead to changes in physical activity.

“What we found in this study is that this network is not only associated with physical activity across the lifespan, but it mediates this negative association. So as age and physical activity becomes negative—it’s the salience network that’s mediating that relationship,” Morris says.

If there is a causal link between those changes and a reduction in physical activity in later life, the implication is that remaining physically active can be even more challenging the older we get.

“We should be ensuring that people are maintaining physical activity through midlife long before they start to see declines in physical activity that are due, in part, to mechanisms in the brain, with the goal of shoring up those cognitive resources that are helping them engage in physical activity,” Morris says.

“What we’re starting to see is that this is all a closed loop,” he adds. “Physical activity can benefit the brain, and the brain benefits our ability to voluntarily engage in physical activity.”

The next step for Morris and his team is to move closer to causation by conducting a follow-up study that would involve modifying participants’ salience networks, randomizing them into two groups and observing changes in physical activity.

“I came to Northeastern to specifically understand how and why people engage in physical activity, and what we can then do to help people modify their behavior with specific insights,” he says.