Sitting more than eight hours a day without any added physical activity puts your risk of death at levels similar to obesity and smoking. Meanwhile, sedentary jobs in the US have increased 83% since 1950, and physically active jobs now make up less than 20% of the US workforce.
Modern life has become an evolutionary mismatch for the movement-heavy lifestyle our bodies need to stay healthy. Our hunter-gatherer ancestors had to move to do just about everything, so human physiology evolved to require constant movement. But today, we commute in cars, work at desks, and order our meals via smartphone apps.