Too good to be true? Experts clash on whether hitting the gym helps the brain

The study came with impeccable pedigree — published in a peer-reviewed journal, using the most rigorous approach — and it seemed to prove what countless worried baby boomers want to believe: that breaking a sweat is good for the brain.

Researchers had older women with mild cognitive impairment, which often becomes Alzheimer's disease, exercise twice a week for six months. In women who did resistance exercises — with weights, for instance — or balance training, the size of the hippocampus decreased about 2 percent, on average. But in women who did aerobics, this memory-forming structure increased 4 percent, scientists reported in 2015. The 6-point difference was hailed in dozens of news stories, with headlines calling exercise the brain's "miracle drug."