Not only a great pedometer and workout tracking app for iOS, Cardio Smackdown lets you challenge others to a simultaneous workout via Game Center.
Cardio Smackdown tracks treadmill, elliptical, outdoor run/walk/hike, and even biking. You can workout solo and track your workouts – even share the workout on Twitter or Facebook – or you can challenge your friends or anyone via Game Center to a real-time workout.
When doing your social workout, you'll see your opponents progress right along side of yours. A great way to take the monotony out of long workouts!
You can keep your iPhone in your pocket as well and be updated via Cardio Smackdown's audio updates letting you know your progress.
Cardio Smackdown also lets you access your iTunes library so you can choose the right entertainment to get you through the burn.