this is also my understanding that the body needs to rest and repair.
I do not believe that “The Biggest Loser” is supposed to be the blueprint for an exercise program. It is a TV show to entertain with a highly selected group of participants and a medical staff standing by.
But to expand on your observation: there are many people who do something physical 7 hours a day. In their cases, it is called ‘work’ and is physical labor. They have usually built up to the ability to sustain such workload over time.