Imagine your kid is running into the street and you have to sprint after her in bare feet," Eric told me when I picked up my training with him after my time with Ken. "You'll automatically lock into perfect form--you'll be up on your forefeet, with your back erect, head steady, arms high, elbows driving, and feet touching down quickly on the forefoot and kicking back toward your butt." You can't run uphill powerfully with poor biomechanics," Eric explained.