The Biggest Loser: how do they do it?

I've been wondering how the contestants on the Biggest Loser manage to work out at the intensity and length that they do day in and day out.  After paying attention to the show for many seasons and reading about it on the NBC website it's not hard to understand how they are able to drop weight the way they do. The dramatic weight loss (8+ lbs a week) requires contestants to workout and burn approximately 5,000-6,000 calories a day in exercise while maintaining a diet that is just below their basal metabolic rate (the number of calories you burn in a day of just rest).  They eat a low calorie diet with a specific percentage of carbs, fats and protein. Then at a minimum they do two hours of intense cardio and one hour weight/strength for approximately three hours a day.  I get the diet part.  I don't wonder about that.  It makes sense to me.  What I don't understand is how they do (a minimum) of three hours a day of intense exercise seven days in a row.  How do they do all if this and manage through the fatigue and avoid injury (not every contestant has been injury free but the majority are).

While racking my brain I think "wow they must be determined", but then I think about my toughest training weeks during Ironman.  I was determined to be the most prepared but I don't think I could have done 3 + hours of working out everyday with no rest days or days with reduced intensity.  The questions that come to mind are: How do they go from little exercise to 21+ hours a week?  When do their muscles recover? What about the muscle fatigue?  Do they take ice baths every night?  How do they manage to have the electrolytes to not bonk during workouts (it doesn't look like the use a sports drink, wouldn't that mess up their calories for the day)?  Do they get massages every day to deal with the muscle fatigue?

I'm not questioning the biggest loser program itself, in fact the show brings tears to my eyes when I watch the success each member has.  I understand that these people are at a point where drastic measures must be taken.  They have seasons and seasons of proven success so the program works.   I just want to know the secret.