Found the article you referenced:
http://www.newyorker.com/magazine/2010/11/08/the-perfect-stride
"[According to Johnson, sprinters retract their trailing leg quickly for two reasons: it generates power, and it means that the foot has a shorter distance to travel before it arrives back in position for another stride. Salazar said, “One thing sprinters say is: Go to the ground. Don’t wait for the ground to come to you.†By “going to the butt,†he believes, Bekele can take more strides per minute—which gives him greater speed.]"