Ronda Rousey, one of the most influential stars in UFC history, revealed this week that she retired from mixed martial arts primarily due to a history of concussions.

Rousey retired from MMA at the age of 29 in 2016, after back-to-back knockout losses to Holly Holm and Amanda Nunes. During an Instagram Live to promote the upcoming release of her memoir, "Our Fight," Rousey, now 37, said a long history of concussions suffered in her previous sport, judo, contributed to her decision to leave MMA.

"I'd like people to understand my reasons and motivations behind things," Rousey said. "I was forced to leave fighting when I was faster, stronger, more skilled and had a better understanding of the art than ever before. It was a really hard decision to understand, one that my body made for me."

The UFC signed Rousey as its first-ever female fighter in 2012. The former Olympic bronze medalist in judo quickly rose to fame in MMA, due to a string of first-round wins via armbar. She made her UFC debut in 2013 and defended the UFC's bantamweight championship six times before suffering a devastating head kick knockout to Holm in 2015.

Following that loss, Rousey essentially went into hiding from the media and MMA community. During her Instagram Live, she said part of the reason she never spoke in-depth about that loss is that it was impossible to genuinely do so without mentioning her concussion history, which she felt she had to keep private in order to compete.

"I think there was just so much to [that loss] that I couldn't talk about it in the form of an interview or article or anything like that, or there would be several filters between my words and people reading it," Rousey said. "So much had to do with having so many concussions when I was in judo before I even got into MMA. I couldn't talk about it at all when I was doing MMA, because it would literally put a target on my head and I might not have been allowed to compete any farther."

Rousey (12-2) went on to perform in professional wrestling with multiple companies, including the WWE, following her retirement from MMA. She was inducted into the UFC's Hall of Fame in 2018. UFC president Dana White has credited her as the only reason he changed his mind in 2012 to promote female martial arts.