HOW: Start in the low plank position with forearms on the ground and your elbows directly under your shoulders. Your toes should be pushing into the ground. Drive your elbows into the ground and while keeping your back flat and knees straight, push your body back and forth using your shoulder muscles exclusively.
FEEL: You should feel the muscles in your core and shoulders working.
COMPENSATION: Keep your elbows in line with your hips and feet, don’t bring them too far out or in. Keep your back flat and knees straight as you move your body with your shoulders. Don’t move your body just by moving your feet!