Swimming sensation Michael Phelps spent countless hours in the pool training to become the most decorated Olympian in history.
He also spent countless hours in bed, sleeping.
Phelps says training and sleeping were equally critical when it came to acquiring his stack of 28 Olympic medals.
"At a very young age I learned how important sleep was," says Phelps, who spoke to CNBC about his training habits from the New York City showroom of direct-to-consumer mattress brand Leesa. The Olympian has recently entered into a four-year brand partnership with the company.
Sleep is "where you can naturally grow and your body recovers," says Phelps.
When Phelps was training for the Olympics, he swam seven days a week, covering between 70,000 and 100,000 yards a week.
As part of his workout regimen, Phelps tracked not only how much sleep he got but how deeply he slept. He made note of the quantity and quality of his sleep and data points such as whether he was getting REM sleep, deep sleep or light sleep.
"I really can't say it enough. I don't think people really pay enough attention to how important sleep is," says Phelps.
He was in the pool three to five hours a day seven days a week. To maintain that workout schedule, Phelps slept eight hours a night and took a 2-3 hour nap each afternoon, he says.
Now, though he's retired from swimming, Phelps still tries to get at least eight hours of shut eye a night. But, since he has a nine-month-old baby, that's a challenge worthy of an Olympian.