TIME spoke with the author of Run! 26.2 Stories of Blisters and Bliss mid-stride about trekking around the globe and surviving 50 marathons in 50 days.

Charles Sykes / AP Kelly Ripa and Regis Philbin interview ultramarathon runner Dean Karnazes at the completion of his Run Across America at "Live! with Regis and Kelly" studios in New York, May 10, 2011.

Ultramarathoner Dean Karnazes, 49, puts his iPhone to good use while he’s running, both to dictate his books and to do interviews en route. “I think I have some of my clearest thoughts when I’m out running,” he explains. The story of his remarkable athletic career appears in the new paperback edition of his bestseller, Run! 26.2 Stories of Blisters and Bliss. We caught up with the author — not literally, of course — by phone mid-run in Marin County, California.

Your running accomplishments are legendary. What’s your longest continuous run?

I recently ran more than 3,000 miles across America. That was 75 days of nonstop 40-50 mile days. I only stopped at night to sleep for a few hours.

How far have you run at one time without stopping?

350 miles.

How was that possible?

With a lot of sleep deprivation. (Laughs.) I ran for 81 hours and 44 minutes.

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Tell me about your 50 marathons in 50 states.

There’s a club of people who have run a marathon in every state. I was talking to a guy who was running his 50th marathon in Big Sur. I asked him how long it took him, and he said, “Eight and a half years to hit my goal.” I was captivated by it. I really wanted to do it, but I have a young family and work obligations. So I decided to do it in 50 continuous days.

Unbelievable! Was it fun? Was it grueling?

It was all of the above. It was insanely exhausting, fatiguing to the point where I wasn’t sure I could get out of bed some mornings, let alone run a marathon. A lot of people say, “I can barely walk up stairs for a week or two after running one marathon. You were doing it day after day for 50 days.” I had my family with me a lot of the times, and the kids were being home-schooled. We met some of the most amazing people and really got to see this country. We raised lots of money for kids’ outdoor activity programs. But even more than that, I think we inspired a lot of kids to run.

You write about the fact that people will run along side you on these runs.

When I ran across America last year, there were thousands of people who joined me along the way. They brought food and presents. It was wonderful.

What are the most exotic places you’ve ever run?

Antarctica certainly was amazing. And the Atacama Desert in Chile, the driest place on earth. There’s never been recorded rain, ever! It’s a Mars-scape.

Any that have been painfully boring?

When I was running across the country, I was doing 40 or 50 miles a day in sleeting snow with zero visibility for five or six days in a row. Ten to 12 hours of running in that is monotony beyond belief.

Your dedication to your wife in the book was beautiful. (“To my lovely wife, Julie, thank you for faithfully putting up with me for all these years. We’ve had some fun, and we’re not done yet!”) How has she been supportive of you?

I’ll just give you an example of her character. Here I was, this corporate guy that was very unhappy in the corporate world. I finally said to her, “Julie, I don’t know how I’m going to do it, but I’m going to become a runner. I don’t know how I’ll make a living doing it. I mean, it’s scary — I’m going to give up all my perks, my stock options, my healthcare. And she looked at me and said, “I’m really surprised that it’s taken you that long!” She’s just been that kind of supportive wife.

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How have you avoided major injuries?

Knock on wood — knock on the side of my head — I don’t know. I’m 100% Greek, and I have really good biomechanics. I’ve been analyzed on the treadmill and sliced and diced by doctors and scientists. My alignment is really good for running; my foot does not pronate or subonate; my foot strength is what they call “true.” A lot of that is hereditary. I spend a lot of time cross-training. I have a elliptigo. It’s a standup bicycle. You don’t pedal; you stride on it. It allows me to have the same striding motion as running without the impact.

You must have a ferocious appetite for food!

When I ran across America, for 75 days I ate 10,000 calories a day. I still lost about five pounds.

Do you any advice for mere mortals, people who are just recreational runners?

Start from the ground up. Invest in a really good pair of shoes. Go to a specialty running store and work with a knowledgeable floor salesperson. Get fitted for the right shoes. Change your course and keep it fresh. When you’re feeling lazy — “I’m not going to do my workout today. I’m just going to have some pizza on the couch” — look six months down the road and sign up for an event. Having a race to look forward to is a tremendous motivator.