A fighter's chin and ability to 'take shots' is always a focal point of discussion in MMA. If Melvin Guillard had a better chin, he could be a champion, if Chuck had been more concerned with how many punches he absorbed then maybe his chin would have lasted longer and he could have won a few more fights, etc etc.
It's usually pretty hard to tell when 'the life' has caught up to someone...when they have reached the point where they can't take the punishment they used to be able to take, or should be able to take. Most of the time, you have to look back, and see where a fighter started to seem to get rocked or knocked out a lot easier then before(with guys like Chuck and Wanderlei, it isn't too hard to pinpoint 'Which KO did it')
I'm going to go out on a limb and say that I believe Mir's chin, relative to whatever it was, is gone.
For starters, Frank Mir has 5 career losses. Fun fact: All 5 losses are by TKO or KO. Of those 5 knockouts, 4 have come in the very 1st round.
One of the stand out aspects of Mir's losses is that he isn't suffering one punch knockouts, but rather, accumulating a lot of damage leading to the eventual stoppage. Against Freeman, Cruz, and Lesnar...Mir's opponents worked ground and pound steadily from on top. They landed blow after blow and slowly worked Mir to a point where he could not continue or the ref stepped in to stop the fight. It wasn't a one punch knockout...it was Mir eating a LOT of shots and taking a lot of damage leading to a prolonged TKO stoppage.
Brandan Vera was the quickest of any defeats. One straight right hand staggered Mir, a big knee dropped him, and a few followup shots finished the job...all in about a minute.
And along came Carwin...
Carwin pressed Mir up against the cage and unleashed brutal dirty boxing, serving up many uppercuts. Mir fought unconsciousness...but Carwin kept pouring on the pressure...landing big shot after big shot and the referee did not step in to stop the fight until Mir was completely unconscious. This was the first actual KO of Mir's career...as opposed to TKO.
Since then, Mir hadn't had too many problems. Mirko Cro Cop took the fight with Mir on about 4 weeks notice, and was far to gunshy to test Mir's chin. The pneumonia stricken Roy Nelson failed to really do so either.
Last night, Frank Mir won, breaking Nogueira's arm to do so. But it's the action before that is concerning. Nogueira has never been known as a power puncher, he has 3 career wins by knockout or TKO. But he had Mir BADLY rocked last night and could have very easily finished Mir with strikes.
I think all of the damage and just the fact that he has had so many fights, so many training camps and etc is all catching up to Mir. I don't think he can take punches that well any more. I mean, having 100% of your losses coming by knockout or TKO is bad enough...but to now he is even being badly rocked in winning efforts.
I don't think Frank Mir has passed his prime yet...but I think he is at a point where he is passing it...these are the years where his performances start slipping...he hasn't looked great in quite a while. Once you start to really slip, once your chin starts to go...it's pretty much impossible to bounce back completely.
I'm not sure who his next opponent will be, Lesnar, Overeem, Cain, or Dos Santos(I would like to think that it SHOULD be one of them) but I'm almost positive that whoever it is will knock him out.