Greene is well-known for being Oprah Winfrey's personal trainer.
In his latest book, "20 Years Younger: Look Younger, Feel Younger, Be Younger!" Greene gives advice for living well and looking good as you get older.
Read an excerpt from "20 Years Younger" below, then check out some other books in the "GMA" library.
Several years ago, I spent part of the spring cycling my way across the country, riding from Long Beach, California, to New York City. It was something I had always wanted to do, and the opportunity presented itself when I was booked on a multicity tour to promote a book I'd written. I knew that the 3,600-mile trip would be grueling, but I thought it would actually be less stressful than racing from one airport to another, which is how a typical book tour unfolds. To prepare, I trained hard so that I'd be able to hit my target of riding about one hundred miles a day. I planned to sleep in a different town every night and visit bookstores, malls, and fitness centers in more than thirty cities along the way.
I wasn't far into the trip when I began to feel dramatic changes taking place. By the time I hit Arizona, I had a mental and emotional clarity that I'd never before experienced. At times, I'd be riding for eight hours or more with nothing but the sound of my own breathing and the beat of my heart in my ears. As I looked around me, colors seemed brighter, the world smelled fresher, sounds seemed sharper, the things I touched seemed more textured. All my senses were amplified. And nothing rattled me -- not a dog giving chase, rain on my back, a treacherous ascent. As my legs cycled rhythmically, the pedestrian concerns of the everyday slipped away and I'd find my thinking stripped down to the essentials. I contemplated the scenery and I contemplated my life. What was important to me? What did I want out of life? While I was on that trip it all became so much clearer.
As I edged toward Chicago I became aware that I was also going through extraordinary physical changes. I'd been hailed on at the Grand Canyon and twice climbed more than 11,000 feet in the still snowy Rockies, and I felt invincible, virtually bulletproof. Every night I slept like a rock. In my early forties at the time, I thought I was pretty fit going into the ride, but that extreme physical challenge left me much stronger than I'd ever been in my life, even in my twenties.
While I knew riding cross-country would be a challenge and that I'd come off the bike fitter than when I started, I hadn't realized how much the trip would transform me both physically and emotionally. I was particularly amazed at how clearheaded I felt. I was able to look at my life and see exactly where I wanted to go. By the time I reached the East Coast, I was operating on all cylinders and had regained (and even significantly surpassed) the strength, power, energy, lucidity, and drive of my earlier years.
Graduate students in exercise physiology learn about the anti-aging benefits of physical activity, and I was no exception. In fact, I'd had a longtime interest in the science of aging and the prevention of age-related decline. But once my cross-country trip allowed me to see the possibilities for myself, I became passionate about the subject. It wasn't long after I completed that cross-country tour that I started exploring ideas for this book.