People cite activity declining, but really we've been plenty sedentary for all those decades since we eliminated electric public transit in most American cities in the 1950s-60s. Some people walk 20 feet to their car, 200 feet to the elevator, 20 feet to the cubicle, then end the day back at home without scarcely moving 1000 feet by their own leg. That isn't new between 1999 and today. People spend all day inside watching TV or playing video games rather than playing outside, that too isn't new. If anything, more people are biking, hiking, and running outside than they were 20 years ago.
Another potential factor that I think may be a culprit is sleep. Americans sleep less today than 20 years ago:
What is driving this? Well, it could be our addiction to staring at a phone screen for hours at a time in total silence, unmoving. It's probably a combination of things, like the fact that americans are working more hours than they were 10 years ago and now have to sacrifice a good nights sleep to get all their personal business done when they aren't working:
Agreed — I would bet a lack of sleep due to hyperconnectivity, social media, and heavily increased exposure to bright artificial light through smartphones and laptops is the culprit.
The change brought on by this now ubiquitous feature of life may be easy to ignore while we’re in it, but teleport someone from the 90s to now and the first thing they’d notice is smartphones and laptops, not that people are fatter or less in shape.
Another potential factor that I think may be a culprit is sleep. Americans sleep less today than 20 years ago:
https://www.cbsnews.com/news/americans-get-less-sleep-than-2...
https://www.npr.org/sections/health-shots/2019/10/28/7736227...
What is driving this? Well, it could be our addiction to staring at a phone screen for hours at a time in total silence, unmoving. It's probably a combination of things, like the fact that americans are working more hours than they were 10 years ago and now have to sacrifice a good nights sleep to get all their personal business done when they aren't working:
https://www.businessinsider.com/american-work-habits-culture...