Jenny Simpson. Image via: John Walton/ PA Images via Getty ImagesJenny Simpson spent her whole life training her body to go faster than everyone else's. Two months ago, that same body nearly killed her in the middle of a mile run with a group of teenage girls in North Carolina, and she doesn't remember a single second of it.What happened next involved a defibrillator that happened to be nearby, a hospital transfer, and days on life support. Now Simpson is telling her story publicly for the first time, and she's using it to close one chapter of her life while opening another.What happened to Olympian Jenny Simpson?Jenny Simpson was pacing a group of girls through a mile run in Raleigh in June when she collapsed without warning. She has no memory of the moment itself, but Ivy and Joey Pointer do. Joey runs Fleet Feet, the company that hired Simpson as its chief running officer earlier this year, and Ivy works as a pediatric intensive care physician. The couple happened to be carrying an AED that day, a habit tied to their own child's congenital heart condition."When I looked over from afar, I knew that something was very, very wrong," Ivy told CBS News. She grabbed the defibrillator while Joey ran ahead, and stayed with Simpson through the chaos that followed. "I just kept saying her name and kind of screaming her name, honestly," she said.Bystanders performed CPR until paramedics arrived. Simpson suffered a second cardiac arrest before she was transferred to Duke University Medical Center, where she spent days on life support while her husband, Jason, rushed to be by her side.Jenny Simpson’s diagnosisDoctors later diagnosed her with arrhythmogenic right ventricular cardiomyopathy, a rare condition where damaged heart tissue fails to conduct electricity properly. It doesn't come from running, but running is what exposed it. "My cardiologist said, 'You thought you trained your whole life for the Olympics, but you were really training your whole life for June 16,'" Simpson said. "I trained my whole life for that day, and I won."Jenny Simpson bids farewell to sportsSimpson now has a defibrillator and pacemaker, and she calls her cardiologist her "favorite person in the world." What she won't be doing again is competing. In an Instagram post, she confirmed the sport that defined her life is finished for good. "That chapter has ended," she wrote. "Thankfully, my story hasn't."The announcement closes out a career that included three Olympic appearances, a bronze medal in the 1,500 meters at the Rio Games in 2016, a world title in 2011, and two more world championship silvers before she stepped away from elite competition in 2024.What is Jenny Simpson focusing on now?Simpson is recovering at home in Colorado and plans to stay on at Fleet Feet. She's candid about how much remains unknown. "There's still a lot to learn about what my recovery will look like over time," she wrote, adding that she isn't afraid of what comes next because she knows she isn't alone in facing it.She's also asked people to be careful with their sympathy. "Please do not say that you're sorry or that you feel bad for me," she wrote. "If it is true in your heart, please tell me you're glad that I'm here. That's how I feel, so glad that I'm still here."Looking back at the last thing she did before her heart stopped, Simpson finds something worth holding onto. "I'm really proud of that," she said of pacing those young girls around the track. "That's what I'm grateful for. That's what I want to remember."Simpson is recovering well.