Far less has been known, though, about whether and how resistance training affects the brain. A few studies with older people have linked weight training to improved cognition, but the studies have been small and the linkages tenuous. While researchers know that lifting weights builds muscle, it is not yet clear how, at a molecular level, it would affect the cells and functions of the brain.
So, for the new study, which was published this month in the Journal of Applied Physiology, Taylor Kelty, a Ph.D. candidate at the University of Missouri in Columbia, began to consider rats and ladders. He and his collaborators knew that to closely study brain changes related to resistance training, they would need to induce animals to lift weights. But how?
Kelty's solution, a modification of methods used in some earlier studies, involved a 100-centimetre-long ladder and bags of weighted pellets gently taped to the rats' rear ends. The animals received a Froot Loop when they reached the top of the ladder and soon started climbing willingly, even without rewards. After several weeks, the climbers showed increased muscle mass, indicating that the activity was effective weight training.
Next, to test the training's brain effects, Kelty and his colleagues injected a separate group of animals with a substance known to induce inflammation in the brain, creating a rodent form of mild cognitive impairment or early dementia.
Half of these rats then began a weekly program of weight training. As the climbing became easier, the mass of the pellets in their bags was increased, just as people progressively add to the weight they lift at gyms.
After five weeks, all of the animals, including an untouched control group, were loosed individually into a brightly lit maze with a single, darkened chamber. Rodents gravitate toward dark places and during repeated visits to the maze, the animals would be expected to learn the location and aim for that chamber.
But their success differed. In the first few tests, the control animals were fastest and most accurate, and the rodents with mild cognitive impairments faltered. With a little practice, though, the weight-trained animals, despite their induced cognitive impairments, caught up to and in some cases surpassed the speed and accuracy of the controls.
The weight training had "effectively restored" their ability to think, Kelty said.
The untrained animals with mild cognitive impairments, meanwhile, continued to lag far behind the others in their ability to find and recall the chamber.
Finally, to better understand how ladder climbing might have changed the rats' brains and minds, Kelty and his collaborators microscopically examined brain tissue from each of the groups. As expected, they found signs of inflammation in the brains of the animals that had been injected.
But they found, too, that the memory centres of the brains in the weight trainers teemed now with enzymes and genetic markers that are known to help kick-start the creation and survival of new neurons, while also increasing plasticity, which is the brain's ability to remodel itself.
In effect, the brains of the weight-trained rats were remaking themselves to resemble those of brains that had not been inflamed and impaired.
Of course, this was a study with rats, and rats are not people. We rarely weight train by climbing ladders with heavy bags strapped to our rears, for one thing. So, it is impossible to know from this experiment if our brains will respond in quite the same way to lifting weights.
The study also cannot tell us whether aerobic exercise leads to similar, differing or complementary molecular changes in our brains, or if healthy people gain the same benefits as those with impairments.
But the findings are suggestive, Kelty said.
"I think it's safe to say that people should look into doing some resistance training," he said. "It's good for you for all kinds of other reasons, and it appears to be neuroprotective. And who doesn't want a healthy brain?"
Written by: Gretchen Reynolds
© 2019 THE NEW YORK TIMES
