A new iPhone app available on the Apple App Store offers training on the go - using the iPhone as part of the programme.

"REPS: Mobile Trainer is the easy way to burn calories or tone muscles by using your iPhone or iPod like a free weight. Simply curl your iPhone up and down like you would a weight and watch the calories drop in real time", reads the blurb for the new app.

As well as the concept of using the 135 gram iPhone as a free weight, the app brings a real-time rep counter, calorie counter and weight loss targets, while music from the iDevice can be played at the same time as training. There's also "motivational audio messages" from a personal trainer.

REPS: Mobile Trainer is available now for the iPhone and iPod touch for £1.79.