Almost 6 decades ago 5 University of Texas students took the world’s laziest summer jobs. After being subjected to a battery of medical tests, they went to bed…and stayed there practicing inactivity for 20 days, not even walking to the toilet. The only concession was a single, brief shower, halfway through.
The results, now known as the Dallas Bed Rest and Training Study, were eye-popping. Not only were the students weak as kittens at the end of their confinement, but their cardiac function had decreased remarkably. In fact, follow-up studies found that 20 days of bedrest had been harder on their cardiovascular function than the next three decades of aging.
At the time, the primary purpose of the study was to determine how weightlessness would affect astronauts in NASA’s Apollo Moon-landing program. But it sparked a revolution in medical care, with surgical patients being prodded out of bed as soon as possible and cardiologists prescribing exercise, rather than bedrest, for heart patients.
Since then, much research has examined the benefits of exercise, even in limited amounts. Brief exercise “snacks,” such as hurrying up three flights of stairs several times a week, for example, have been shown to be enough to improve the cardiovascular fitness of college students. Comparable amounts of not-quite-as-vigorous exercise have been shown to substantially reduce the risk of major cardiovascular events in seniors.
But these studies focused on only one side of the coin: the value of moderate-to-vigorous exercise, even if it’s only a few minutes a day. Another line of research is focusing on the opposite side of the coin: inactivity.
This research is finding that you don’t have to have to be anywhere nearly as inactive as the participants in the Dallas Bed Rest Study for it to have significant negative consequences. And, a team led by Frank Booth of the University of Missouri, is discovering that cardiac function and muscle strength aren’t the only things that can suffer. Inactivity may also play a role in mental decline and even in the development of Alzheimer’s disease.
The research, says Booth’s coauthor, Nathan Kerr (now with NextGen Precision Health), involved two types of studies, both in rats.
One, published in Frontiers in Aging Neuroscience, compared rats bred to avoid exercise to those that, given access to a running wheel, “might run upwards of 10 kilometres a night,” Kerr says. It found that the non-running rats weren’t as smart at solving problems and remembering their solutions as the ones bred to run. “Their hippocampal function was poor, and their learning and memory continually rated ‘poor’,” Kerr says. “Their rate of neurogenesis, or ability to produce new neurons, was decreased.”
That was intriguing enough, but in a September 2024 follow-up study in the Journal of Applied Physiology, Kerr and Booth’s team immobilized a dozen more normal rats by putting plaster casts on their back legs for ten days, then compared them to a dozen others that had been left free to exercise.
Just 10 days inactivity can affect rat brains
They found that a mere ten days of immobility had dramatic effects in the rat’s brains, especially in the hippocampus, a region of the brain responsible for learning and memory that is highly affected in Alzheimer’s disease. Among other effects, he says, “we were able to recapitulate some of the early pathology seen in Alzheimer’s disease,” including changes in the amyloid protein, “the toxic protein that aggregates and kills neurons in Alzheimer’ disease.”
Not that Kerr thinks a 10-day layoff from exercise will condemn you to Alzheimer’s. If that’s the case, everyone who’s ever sprained an ankle is doomed. What’s important, he says, is to understand the role inactivity plays. In addition to the effects his study found, he says, “[it] exacerbates other risk factors. If you’re inactive, you’re at increased risk for obesity, insulin resistance, type 2 diabetes—all of which are independent risk factors for Alzheimer’s.”
How much exercise should you get for brain health? It’s too early for precise recommendations, “[but I would] stay out of that lowest quadrant of 2,500 steps per day,” Kerr says. And, he says, whenever you can, “break up your sitting periods.”
But that’s a minimum. The day I starting writing this, I logged 20,219 steps. Not that I normally do that much, but I really, really want to keep my brain sharp for as long as I can, and if exercise works, I’m all for it. Because I’d like to continue doing the things I love for many years to come.
And, once you get used to it, getting out and about is fun.
Don’t worry about inactivity, here are the guidelines for the active
