Ronda Rousey says that a history of concussions put an end to her mixed martial arts career.

Before she came one of the biggest stars in UFC history, Rousey excelled in judo, winning a bronze medal at the 2008 Beijing Olympics. This week, she said concussions suffered during her judo career contributed to her retirement from UFC in 2016 after knockout defeats to Amanda Nunes and Holly Holm.

“I’d like people to understand my reasons and motivations behind things,” Rousey said in an Instagram Live appearance to promote her upcoming memoir. “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.”

Rousey was 29 when she retired and has said she suffered from depression and suicidal thoughts after stepping away from UFC. She received criticism for refusing to answer questions about her losses to Nunes and Holm but said in her Instagram appearance that was due to her reluctance to talk about her history of concussions.

“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 was seen as instrumental in giving female fighters a solid footing in UFC. Since her retirement from MMA she has starred in WWE, and dabbled in film and television work.