Walkers always have at least one foot on the ground. They are never airborne.

Runners are completely airborne between toe-off and foot-strike. That makes
running a kind of alternate leg jumping.

There is no more difficult exercise than continuous jumping. Think about how
difficult it is to skip rope or to do jumping jacks or to hop in place for minutes at a
time.

That’s why poor decision-making about speed and distance can make running so
hard.

Running is jumping. Follow that path to a world of insights.