Slim line between weight loss and falling off the treadmill

Fathers and daughters, husbands and wives - even unfit doctors - are signing up for rigorous fitness challenges to shed kilos in super-fast time. And they're not doing it only to get slim - most challenges also offer monetary rewards for the biggest losers.Run by gyms and supplement companies - and accessible online - the challenges have resulted in thousands of kilograms being lost through intense exercise and strict eating plans.