The bird dog exercise is a simple but effective way to strengthen your core and stabilizing muscles. To do the exercise, get down on all fours with your hands and knees shoulder-width apart. Keep your spine in a neutral position and engage your abdominal muscles. From here, extend your right arm and left leg out straight, keeping your hips and shoulders square. Hold this position for a few seconds, then return to the starting position and repeat with the opposite arm and leg.