A cloud of suspicion hangs ominously over the heads of athletes in the UFC, their accomplishments viewed by many through the lens of performance-enhancing drug usage.

The use of PEDs is believed to be widespread throughout professional and high-level amateur sports, but even clean athletes whose accomplishments are the result of their athletic ability, hard work and perseverance, are tainted by the mess.

Little is done to stop the usage in combat sports. Postfight drug testing catches some users, but most experts say it nabs only those who don't understand how to mask their usage.

In fighting, there is no regularly scheduled regimen in which an athlete has to report his or her whereabouts to a testing agency in order to be randomly checked within 24 hours.

So, every time a fighter wins, there is plenty of suspicion that it involved artificial assistance. UFC middleweight contender Vitor Belfort is the latest to feel the backlash. Dan Henderson dodges a punch thrown by Lyoto Machida. (USA Today)

Since it was learned he's been on TRT, Belfort has scored several highlight-reel knockouts and become a legitimate title contender. He's been pressed about the issue so much that he suggested someone beat up the reporter asking about it, a thoughtless move for which he later apologized.

UFC light heavyweight Dan Henderson, who has had an exemption to use testosterone replacement therapy since 2007, said he believes there is a heavy amount of PED usage in the fight game.

"I think there is a decent amount [of PED usage in MMA]," said Henderson, a member of the 1992 and 1996 U.S. Olympic wrestling teams who will fight Rashad Evans in the main event of UFC 161 at the MTS Centre in Winnipeg on Saturday. "Just like at the top level of any sport, there is a decent amount of it. Guys look for that edge."

Henderson is one of a handful of fighters who have been given a therapeutic use exemption (TUE) to partake in testosterone replacement therapy (TRT). Henderson was diagnosed with hypogonadism, leading to his TUE

There are a number of causes of hypogonadism, or low testosterone, including previous steroid usage. Dr. Jonathan Gelber, an orthopedic surgeon who writes the Fight Medicine blog estimated that approximately 1 percent of the population between 18 and 40 who have not used anabolic steroids would be hypogonadal.

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Legitimate TRT user Dan Henderson pushing for Olympic-style drug testing in MMA