It was only a few short years ago that Shane Carwin was on top of the mixed martial arts (MMA) world. But being 38, has taken a toll on the Greeley native. That is why the former UFC interim heavyweight champion called it quits on Tuesday. 

Carwin (12-2 MMA, 4-2 UFC) leaves the sport on a two-fight skid, but more importantly after fighting through injuries and surgeries.

Carwin posted on his Twitter account late Tuesday: "Officially retired 2day:-) thank you to my family, friends and fans! #dreambig GOD BLESS!!!"

Carwin last fought at UFC 131 in June 2011 against Junior dos Santos in a heavyweight title eliminator. He took Dos Santos the distance, but dropped a unanimous decision.

Several months later, he said he expected to be back by the start of 2012. But not long after that, he revealed back surgery would sideline him until the middle of 2012.

That recovery took longer than planned, but Carwin hoped to return in the fall. While recovering, he was tapped to coach Season 16 of "The Ultimate Fighter" opposite Roy Nelson, with a fight planned for December.

But a month before the fight, a knee injury knocked Carwin out of that bout.

And after a neck surgery in 2011, the back surgery and the knee injury, the 38-year-old Carwin elected to hang up the gloves.

I had the pleasure of getting to know Shane, and I can honestly say there is not a person in sports that I would be more proud to say is from my hometown. He is a class act, and although we will miss watching him fight, we will forever enjoy calling him a neighbor and friend. Best of luck Shane!!

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