Get into push-up position with your hands gripping a pair of dumbbells; your hands should be slightly wider than shoulder-width apart, and your feet slightly wider than hip-width apart (a). Keeping your hips parallel to the floor (you’ll need to engage your core and glutes the entire time), bend your right elbow to pull the weight up toward the side of your body (b). Pause, then slowly return the weight to the floor and repeat with the left arm. That’s one rep. Do 15.