Running is the action or movement of propelling yourself forward rapidly
on foot, according to Amy Morris, a Road Runners Club of America
(RRCA)–certified running coach and head of personal training at
CrossTown Fitness, a Chicago-based gym. It’s different from walking
because when you walk, one foot is always on the ground. But with
running, there's a moment when both feet are off the ground. That's what
makes running a high-impact activity.
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