Sonia, I would agree with Harris on this question. The individuals on the Biggest Loser should not be training at this level. It can take years of training to be at that level. I would be interested in seeing statistics on over training injuries for this show and others like it. As noted above, they have doctors, nutritionists and other experts to help them with these issues. Your training is specific to your goals. Many athletes at the higher levels have to train many hours every day in order to be at the top of their game. There are others, as Harris noted, that require long hours of training. I think your question was more in regards to the average person as portrayed in the show. In that case no, as it takes time to adapt the body to that level of fitness, plus learn how to train, sleep and eat properly to maintain it. I should note that you can train hard one day and then do some form of active recovery the next day. This could be anything from stretching to a walk in the park.