Alexander Emelianenko, the younger brother of heavyweight great Fedor Emelianenko, has announced his retirement from mixed martial arts.

In a post that ran on his website and Facebook page, Emelianenko, who went 21-6 in a nine-year career, said he would no longer be able to compete due to "health problems caused by old injuries."

The 31-year-old also thanked both his supporters and detractors for motivating him to succeed, and said he would be focusing more time on his family.

During his heyday, Emelianenko faced some of the sport's top heavyweights, including Mirko "Cro Cop" Filipovic, Josh Barnett and Fabricio Werdum. His most significant win came in a 2006 TKO win over Sergei Kharitonov, though he's more fondly remembered for an 11-second knockout of James "The Colossus" Thompson.

Emelianenko was known for quick fights, as he once authored a eight-fight win streak entirely composed of first-round finishes. At another time, he had three straight knockouts of less than 30 seconds apiece.

In recent years, he had become something of a fighting nomad, competing for seven different promotions since the start of 2007. Prior to his retirement, he had competed four straight times for M-1, and in his most recent match, lost via submission to Jeff Monson. Shortly afterward, he was cut by the promotion, reportedly for violating the terms of his contract. But instead of looking elsewhere, Emelianenko will join his brother in retirement.