Or the breeze, whatever. The three keys, according to Chris Carmichael, are a smooth stride, explosive power, and a strong torso. Here's how to get them: STRIDES, not all-out sprints, mean running as fast as you can while focused on form: back straight, head up, arms pumping in a straight line. Work them into normal runs, four reps of 20 seconds, resting 60 seconds between intervals. Best off pavement. SKIPPING improves fast-twitch muscle fibers and anaerobic power. Work in two sets of three 30-second reps; jog a minute between reps, three minutes between sets. PLANKS create core strength, which generates a quicker, more efficient stride—otherwise you're just flailing. Start in a modified push-up, on your forearms. With legs, torso, and head in a straight line, hold for 30 seconds. Three mornings a week, four reps, resting 30 seconds between. Work up to holding the pose for a minute.