"To run fast, you have to remain relaxed," says Todd Weisse, cofounder and head coach at the Williamsburg Track Club (Brooklyn and New York City) and a volunteer assistant coach at Columbia University.
"When the jaw, face, arms and limbs start to tense up, there's deceleration," Weisse says. "You can either do your workout with pinched eyes and a scrunched-up face, or through a nice, relaxed face and a nice, relaxed jaw."
Relax your face and let your legs do the work.