Outside, which is where human biology evolved, everything is constantly moving. You would be hard-pressed to find a bird, fish, land animal, or insect not in motion. Grass, plants, and trees sway in the wind. Even light, guided by the sun, moves throughout the day. It is no wonder those of us who lead sedentary lifestyles indoors, far removed from our nature, develop all kinds of chronic conditions, like ADHD, depression, and myopia.