Step 1: Lie on your back, knees bent, feet hip-width, directly under your knees, and arms overhead. Roll your pelvis up until your knees and shoulders form a diagonal line. Stretch the left knee and left hand away from each other, so your left side is longer than your right. Let the pelvis shift to the left. Switch to the opposite side. Step 2: Keep your hips high and in line with each other and lift one leg off the floor. Return it to the floor and repeat with the other leg. Runner’s Secret Weapon: A key part of the spring mechanism of running is to lengthen one side of your body and shorten the other. This helps you rehearse that.