Hardest Sport?

What do you think is the hardest sport. I know that it depends on your level and the time commitment that you make however I think that swimming and gymnastics are the hardest two. I know that every one works hard at what they do and you are partial to your sport (I swim) however I don't see many sports training year round and doing doubles every day along with weights and dryland plus running. Swimmers spend like 4-5 hrs. a day at practice at that is at the highschool level. And we do this almost year round. I do know that in gymnastics it can be very demanding especially because they usually train so intenstly at a very young age. Some of them even live at the training center Geez.... I was talking to my friends and they do a wide variety of sports and they say that while theirs may be harder for a few weeks swimming requires a long term commitment and you can't depend on anyone else but your self. Any way what are your thoughts???