Bird Dog Geisel said bird dog is one of the most underrated exercises. "People look at it and they just think that it's super simple and a waste of time, but a bird dog is actually quite challenging." Get on all fours, with your knees under your hips and your hands under your shoulders. Remember to keep abs engaged and keep your back flat. Reach out with your right hand and extend your left leg out behind you. Round your back and head to connect your right elbow with your left leg under your body. This completes one rep. Image Source: POPSUGAR Photography