Working out is no picnic, and it's especially hard if you've been sitting around and are in terrible shape. Just ask the contestants on 'The Biggest Loser.' Now add to that the emotional turmoil and natural rebelliousness of being a teenager, and you've got 'I Used to Be Fat' (Tue., 10PM ET on MTV).

It was no surprise at all that Holly completely lost her cool during a simple jogging exercise. And over how many laps she'd down and how much more there was to go. She thought she should be done while her trainer Chris said there was one more lap to go.

So Holly quit running and started yelling and fighting with Chris, even going so far as to curse. In the end, though, she learned to stick with it and work through the emotions. Now she's down 31 pounds and healthier and happier.

It's certainly a far cry from the girl screaming at her trainer on the track. But that's the same girl who put all the weight on in the first place. Hopefully, she's in a better head space to go along with her slimmer and healthier body.