Lay flat on your stomach, position your elbows under your shoulders, curl your toes under, and push your body up by resting your weight on your elbows and tightening up your torso. This can be done by pulling your navel in toward your spine so that your hips don't sag. Your body should be in a straight line from head to heels; the neck should be kept in line with the rest of the spine. Keep breathing naturally throughout the exercise. Hold for about 30 seconds. Make the exercise less challenging by holding this position on your knees or by placing your forearms on an elevated surface. Make it more of a challenge by bringing in a leg lift.