Retired gymnast and 2010 U.S. floor exercise national champion Mattie Larson appeared on ABC' Good Morning America recently, and told the story of how she purposely injured herself to avoid contact with recently sentenced former USA Gymnastics doctor Larry Nassar.

Larson told anchor George Stephanopoulos about the time she intentionally poured water on her bathroom floor and "slipped" so she would hit her head. The former gymnast did this when she was 15 or 16-years-old so she wouldn't have to go to train at Karolyi Ranch in Huntsville, Texas, when Nassar often assaulted gymnasts.

"I was crying, panicking, didn't want to go. I was taking a bath. It wasn't even a hard decision in my mind. I just turned on survival mode," Larson, who is now 25-years-old, said. "I banged my head as hard as I could to make sure that I got a bump and to make sure that my parents heard the bang."

Stephanopoulos asked why Larson felt she couldn't go to her parents for help. "It wasn't an option for me. I didn't know I could. I didn't have a voice," Larson responded.

Larson also touched on the complicated feelings surrounding testifying against Nassar in the courtroom. "It was like probably the most intense situation of my life emotionally. I felt every type of way. I felt sick, I felt like I was going to faint," she said. "I wasn't going to testify; I didn't want to. I didn't want to put myself through it. I didn't think I was capable."

Finally, however, she decided that it was simply the right thing for her to do. 

"On Sunday I decided after going over it a lot and talking through it with my sister and a lot of tears and realizing that it's what I need to do. It's the least thing I could do after all that had happened to me, the least I could do was tell my story so it couldn't happen to other girls," Larson said.

Larson's attorney, John Manly, wants a "full blown investigation" of Karolyi Ranch. "The ranch was put forth by USA Gymnastics as this amazing place where gold medalists were made," Manly said. "But in fact, if you believe the allegations of these women, which I do, it was a house of horrors." 

"I want to find out how this could have possibly happened," Larson said. "He shouldn't have been in my life."

Nassar was sentenced to up to 175 years in jail this week for the sexual abuse of over 150 women.