[westcoast49]

I tend to think it's specifically tied to physical activity. My explanation is that we're conditioned, as a species, to survive by performing physical tasks during the day, to a degree where the brain expects it. If we sit still in front of a computer all day, and do nothing else, it creates a disconnect between what our body and brain is built to expect, and what we actually get.

[ilrwbwrkhv]

I agree that physical accomplishments are easier to quantify by our minds to spin it into a story.