Jessica Ennis-Hill says fear of getting injured and ending her career on a low prompted her retirement from athletics.
The 2012 Olympic heptathlon champion, 30, announced last week she would not carry on to compete at next year's World Championships in London.
"My body can't cope with the volume of training that it used to," she told BBC sports editor Dan Roan.
"It was that fear of 'do I push on that one more year and potentially get injured and come away disappointed?'"
The 2009 and 2015 world champion, who had her first child, Reggie, in 2014, missed out on retaining her Olympic title in Rio by 35 points to Belgium's Nafissatou Thiam in August.
Ennis-Hill said immediately afterwards that she would not rush a decision over ending her career.
"Doing the heptathlon, you've got to be 100% motivated; you have to want to do the training or you're not going to get anywhere with it," she told BBC Sport.
"The past couple of years, I've struggled with injuries and Achilles problems. I'd have sessions that would go really well but then I'd be injured for a few days later.
"Do I say 'I'm in a really nice position here, I've achieved what I wanted to achieve and more' and do I walk away feeling really happy and satisfied?
"That's what I wanted to do."
'TUEs need to be investigated'
Therapeutic use exemptions (TUEs) have been a big talking point in sport recently, with Russian hackers Fancy Bears leaking stolen files from the World Anti-Doping Agency's database detailing the medical records of some of the world's biggest sports stars.
A TUE allows an athlete, for medical reasons, to take a prescribed substance or have treatment that is otherwise prohibited.
Ennis-Hill says the system "is really important for our sport" but that TUEs need to be investigated "if they're being abused".
"We are athletes but we are humans as well and we need certain medication for the benefit of our health," she said.
"We need a system to make sure [abuse] doesn't happen because we want our sport to be as clean as possible."
Although her immediate goal is to "sit back and relax and reflect on what I've achieved" and "spend as much time with my son as possible", Ennis-Hill says she wants to stay involved in athletics.
"I could never walk away from athletics and sport because I love it so much and it's been a huge part of my life," she said.
"I want to do something that I'm passionate about and I'm passionate about getting people active, getting people running and living a healthy lifestyle. That's something that I hope to do in the future."