Working one arm at a time makes the core work more to stabilize your torso while you work your chest.
- Lie on your back with your heels about a foot away from your butt. Hold a dumbbell in your left hand, and bring both hands to the ceiling.
- Bend your left elbow, lowering your upper arm to floor. Exhale and straighten your elbow, pressing the weight back to the ceiling to complete a rep.
- Do 15 reps, then switch arms.
Use a five- to 15-pound weight.