Assume a pushup position, your hands elevated on a rolled mat or low step. Keeping your legs straight, "walk" your feet as close as possible to your hands, rounding your upper back. Actively push your heels into the floor and your palms into the mat or step. Stop when you can no longer keep your legs straight. At that point take a deep breath in and exhale fully. That's 1 breath. Return to pushup position and repeat. Don't shrug your shoulders or rush your breathing.