And while Americans have cut down on walking, they’ve been putting on some pounds. A recent study found that about 35 percent of adult Americans are obese, as NPR’s Shots blog reported in January. That equals “more than 78 million adults and more than 12 million children.”

As one example of how people can take a technological advance and turn it into a reason to stop exercising, Vanderbilt points to the moving sidewalk.

“Go to an airport, and look at people on the moving walkway,” he says. “I mean, the engineers who built that walkway — it’s meant to speed you up, by walking on it. You’re not meant to just hop on it and go on a slow, sort of moving ride.”