While water-skiing at age 29, Dr. Kenneth Cooper thought he was having a heart attack. At the hospital, his doctor told him he was simply out of shape, having gained 40 pounds and become inactive due to the stress of medical school. Cooper lost the weight and started to exercise. His health scare triggered not only his first book, the 1968 best-seller "Aerobics," but also a fitness revolution. He has now written 19 books, which have been translated into 41 languages with more than 30 million copies sold.

Cooper, now 76 years old, is a former Air Force physician and founder of the world-famous Cooper Institute in Dallas.

Q. How did you discover the impact of cardio fitness on the body?

A. One of my responsibilities as an Air Force flight surgeon was to develop a conditioning program to be used by NASA to prepare astronauts for prolonged weightlessness in space. Three important questions had to be answered: 1) What type of exercise is most important? 2) How can you compare aerobic exercises? 3) How much is enough?

The answer to the first question is that only aerobic or endurance-type exercise has the potential to provide cardiovascular conditioning.

The answer to the second question, how to compare aerobic exercises such as walking, running, cycling and swimming, was to develop an aerobics points system based upon the duration and intensity of various activities. There are 41 exercises that qualified as being aerobic and could be awarded aerobic points. The top five are cross-country skiing, swimming, jogging/running, cycling and walking. Running 1 mile in eight minutes was worth five points, but walking 1 mile in 18 minutes was worth only one point. If you ran 3 miles in less than 24 minutes, it was worth 17 points, since endurance points were added.

The final question was, in effect, how many points per week were necessary. The answer was 30 for men and 28 for women in order to see a significant improvement in the body's maximal oxygen consumption, which is the best way to measure endurance fitness.

Q. When you lost those 40 pounds by exercising, did you notice anything else happening to your body?

A. My feelings of lethargy, easy fatigability, early hypertension and lack of an overall feeling of well-being disappeared.

Q. You are credited with coining the term "aerobics." How did you come up with that?

A. While preparing the manuscript of my first book, "Aerobics." From my medical school days, I knew that the word aerobic means "living in oxygen," and since the goal of my program was to improve the body's capacity to utilize oxygen, I took the adjective aerobic, added an "s" to it, and made it a noun. I titled the chapter on endurance exercises "Aerobics" and sent the manuscript off to the publisher in New York. He thought that was unique and said, "Let's call the book 'Aerobics.' " I disagreed, saying people won't be able to pronounce it, they can't spell it, they won't remember it, but all I can say is that after 40 years he was right and I was wrong.

Q. Can you explain the idea of being fit but fat?

A. In no way am I endorsing obesity. But our studies clearly show that, if you look at cardiovascular mortality and even cancer mortality, you are better off being fat (over 30 on the BMI scale, 25 percent body fat), and fit (ranking in the top 80 percentile on fitness tests) than being thin (less than 20 on the BMI scale, less than 17 percent body fat), and in the bottom 20 percentile for fitness. Having done more than 250,000 treadmill stress tests on more than 100,000 people in the past 30 years, I feel that I can safely say that you are better off being fat and fit than skinny and unfit.

Q. Do you think we've overemphasized aerobics in comparison to other components of fitness, such as strength training?

A. Aerobics is only a part of a total conditioning program that includes proper weight, nutrition, exercise and proper supplementation. Proper exercise includes strength training and flexibility.

Q. What's in your refrigerator right now?

A. Hopefully you will find healthy foods, including skim milk, fresh fruit, raw vegetables, bottled water and, yes, a small can of regular Pepsi. One of my vices is having an 8-ounce can of Pepsi four or five nights a week.

Q. Your favorite junk food?

A. Chocolate-chip cookies.

Q. Your favorite healthy breakfast?

A. Half a grapefruit, unsweetened oatmeal and a glass of skim milk (followed later with a half-cup of decaf coffee), and eight vitamin and mineral supplements.

Q. What's the world's most perfect food?

A. I do not think there is a single perfect food, but it is a combination of fruits and vegetables, which are so important. If I had to choose a single perfect food, I would probably select salmon, which has a multitude of good qualities, including a high level of omega-3s.

Q. What was your worst summer job?

A. Working at the Wilson Meat Packing Plant in Oklahoma City while I was in high school. I worked in the area where we had to hydrogenate oils to convert them from liquid to solid form, and it was not until a few years ago that I realized how bad was the product we were producing. Hydrogenated or partially hydrogenated oils are two of the worst things you can consume if you are trying to protect yourself from cardiovascular disease.

Q. As a child you wanted to be?

A. From age 5, my family told me, I started talking about being a medical doctor, and I never wavered from that career goal.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.