Ohno is training for the 140-mile Ironman World Championship later this year in Kona, Hawaii.
For instance, today Ohno is going on a 112-mile bike ride that will last 7 hours, give or take 30 minutes!
"Originally I thought 'It's impossible, this is just not for me, I'm a sprinter'" he said of taking on this task. "The longest race in my entire career that's endurance was about 2 minutes, 10 seconds. That's not even close!"
Other crazy training days include two-hour runs, and 3,500-meter swims (that's more than two miles in the water)!
"I want show up in Kona and have zero regrets," Ohno said of his intense training.
What goes through the mind of a finely-tuned athlete while he's on the bike for seven hours?
"I do a lot of meditation, during the Ironman -- people don't know but you can't listen to music, you can't have any electronic equipment it's just you against yourself, there's no hiding from the pain," he said. "A lot of things go through my mind, sometimes I think about food, that's the most difficult part."
Ohno said he craves the gamut of food, including Chinese, pizza, burgers and fries. He's training upwards of 20 to 30 hours a week.
"I think the fact it had been four years since I retired, I wanted to do a new challenge, I needed something in my life," he said of why he signed on for this insane race. "This is competing in the most coveted endurance race on the planet -- 2.4 mile open water swim in the ocean, with 2,000 other athletes clamoring over you, trying to get by you, followed by a 112-mile bike ride and then run a full marathon, 26.2 miles, all while battling 100-degree heat, 60-mph crosswinds, and running through the black lava fields and lava rocks. it just seemed so impossible that I've seen people complete it and I said I gotta do this."
The craziest thing is training for this race is not the only thing Ohno is doing.
He has business commitments, speaking engagements, and obviously he's trying to maintain a social life and see friends.
"I definitely don't go out as much as I used to," he said. "But it's made me healthier, strong and also back to feeling like me."
To show fans what he's doing to train, Ohno has partnered with chocolate milk to film eight webisodes showcasing his journey. He's filming No. 5 right now.
He said in addition to drinking chocolate milk post workouts, he "eats for my activity, so if I have a day where I don't have a ton of activity, I minimize my carbs and focus on protein and vegetables."