Start in a plank position with your hands on the mattress.
Pull your abs in and squeeze your glutes to stabilize your core. Inhale and bend your elbows to lower your head toward the bed; exhale, pulling your navel to the spine, and straighten your arms, returning to plank.
Too easy? Flip your body around so your feet are on the mattress and do push-ups this way.
Complete three sets of 10 to 15 reps (do fewer reps if your legs are elevated).