The Biggest Loser - big numbers?

Watching the Biggest Loser Season 12 on NBC. Was wondering how those people managed to pull in such big numbers per week - averaging at around 7 pounds loss per week. If you need a deficit of 3500 calories to lose a pound, that's a deficit of 24500 calories per week to lose their 7 pounds! That is to imagine each person having to do workouts that burned a total of 3500 calories per day....Mind blowing numbers. Especially when I think about the fact that I can only burn ~400 calories with 5k run (37 min). Geesh.