DEAR DR. DONOHUE: “Walking, walking, walking” is all I hear. All the talk about it makes me wonder if it’s really the be-all, end-all it’s made out to be.

I am a 76-year-old woman and haven’t done anything athletic or done anything in the way of exercise since I was in grade school, and I didn’t do much then. I did raise five children and kept house for my family. Does that count? Now I’m told I can live to be 100 if only I take up walking.

I’m trusting you to give me the truth about this, and I’d like to know some of the specifics, like how fast to walk and how far. — M.Y.

ANSWER: Raising five children and keeping house for your family qualifies as exercise.

No one in medicine or in the health field says that inactivity is better than activity. Study after study shows exercise prevents heart disease, keeps arteries supple and lowers blood pressure. All of this is true. Furthermore, it keeps fat off the body.

Walking is so heavily promoted because just about everyone can do it, no special equipment except for walking shoes is required, and no special athletic talent is needed. We’ve all been walking since infancy.

Thirty minutes a day on most days of the week is the goal. Those 30 minutes don’t have to be consecutive minutes. You can break down your session into three 10-minute periods.

The pace should be around three miles in one hour, one mile in 20 minutes. If that is too fast, then walking one mile in 30 minutes is sufficient. If you choose the lower speed, gradually pick up the pace as you get used to exercise.

If you want to measure in steps, a leisurely pace is 80 steps a minute; 100 steps a minute is a brisk pace.

Everyone has a fascination for calorie burning. If you’re 120 pounds, a brisk walk burns about 85 calories in a mile; for 160-pounder, that’s 105 calories; for a 200-pounder, it’s 125 calories.

DEAR DR. DONOHUE: I’ve never had a response from you to anything, so I thought, why not one more time?

I have a marathon coming up. I am now running six hours. Every time I hit the six-hour mark, I hit the wall. Why does this happen? My mind says, “Go.” My body says, “Stop.” I hydrate properly, I train and run with my own hydration pace, I eat a good breakfast before I start, and I am healthy. What’s going on? — C.K.

ANSWER: I apologize for not answer your previous questions. I’m late with the hitting-the-wall question. What can I say?

“Hitting the wall” is the point of complete exhaustion. It’s believed to be due to a depletion of all stores of glycogen, the carbohydrate stored in muscle and the fuel that supplies energy for aerobic exercise such as long-distance running. It’s true that with glycogen depletion, the body shifts to fat burning, but sometimes the shift isn’t as effective as it should be.

Drink beverages before and during the run that contain carbohydrates. The carbohydrate content of the drink should not be more than 8 percent.

How did you do in your marathon?

DEAR DR. DONOHUE: I have a friend, a high-school biology teacher, who says that people burn more fat when their exercise is less demanding than when it’s quite hard. What do you say? — L.H.

ANSWER: It’s a point that comes up every few months. Low-intensity exercise does burn a higher percentage of fat than high-intensity exercise, but total fat burned is much greater in high-intensity exercise. If fat burning at low-intensity is 60 percent of calories and 40 percent of calories at high-intensity, high-intensity exercise burning 1,000 calories yields far more fat calories than low-intensity exercise burning only 100 calories.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.

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