What's the most physically exhausting sport? (at professional level)

I would have thought MMA/Martial arts are pretty high up there. Not only do you have to contend with constantly moving, being alert, keeping balance, and putting as much force behind your blows as you can which often involves a lot of work from your entire body, you also have to deal with what ever your sparring partner/opponent throws at you and you have to deal with the pain and injury sustained, reacting to how they move, and the psychological aspect. Although fights don't usually last very long.

Apart from that, I'd say it would have to be endurance sports like a marathon or the Iron Man competitions.

I would have thought that any sport which is based more on physical condition rather than skill would be equal. Things like rowing, running, cylcing should be the same because you have to push yourself to the max or the other person will push themselves harder and win but when i watch pro athletes they never seem that tired at the end which makes me wonder why they didnt push themselves harder. I have pushed myself so hard that I have collapsed or cannot stop being sick and I did that for no reason except to try and beat my pbs. I dont even take sport seriously so it makes me wonder why athletes can do interviews and things straight after, the should have just ran a bit faster and won the race. Its not true that althletes dont need to train as much for high intensity sports. Everyone is trying their hardest so you cant make up for being in poor shape by just trying harder than the others. I will go with marathon running as the most soul consuming just because of the length of time, I can imagine finishing the first mile and thinking there are 25 more to go, it must be horrible.

Cross country skiing (I'm sure I read that they generally have the highest VO2 maximum anyway), boxing, ultra long distance ****, blablabla.

Squash.