Generations: The Real Differences Between Gen Z, Millennials, Gen X, Boomers, and Silents—and What They Mean for America's Future

by Jean M. Twenge

The cost of the digital age isn’t just mental—it’s physical. Around 2012, just as smartphones became common, the number of teens who said they rarely exercised increased, reaching all-time highs among both 8th graders and 12th graders by 2019 (see