Plank up + down This exercise is fantastic for strengthening your shoulders and core strength. Sarah Lawrence shows us how.The goal is to maintain a solid plank position throughout the whole exercise and to not let your hips sway.Starting on your elbows and toes, or for Level 1, on your knees, engage your core before you start. Keep your hips as still as possible, push up with one hand then the other until you are propped up in a push-up position.Lower back down to your elbows one arm at a time. Halfway through, change your leading arm so you strengthen the other shoulder as you press up to your hands.NEXT: Advanced plank variations>>