Imagine how bored you would get. It would take me a day or two before I would be craving some physical activity. Think of all the things you could think about, all the philosophical existential questions you could ponder over... for 90 days. Am I scaring you yet? There's nothing in the article about what NASA or the people conducting the test would do keep you entertained. Presumably you can play the wii lying down, watch movies and listen to music? Anyway, just the thought of no physical activity for that much is killing me (I'm saying this even though I'm not a fitness lets run 10-miles-a-day type). It's one thing to stay in bed for months to go to Mars (I would), its completely another to do it here.