Meet the Shadowboxer: an app enhanced cardio trainer that lets you work on your upper arms, shoulders, and back. It can be used to add more intensity to your favorite workouts or get you warmed up for crazy weight training or running sessions. The Shadowboxer consists of a waist belt with resistance tubes.
This cardio trainer combines with your smartphone to let you compete against virtual opponents. The belt and handgrips have adjustable settings. You can get yours here.