DEAR DR. DONOHUE: I have been doing weight training since I was 14 and have been pedaling a stationary bike for 20 years. My resting heart rate upon awakening in the morning is 62 to 66. Using my new heart-rate monitor, I see that my rate goes up to as much as 182 near the end of my 40-minute bicycle ride. This is beyond the rate suggested for a 59-year-old. Is the high exercise heart rate harmful? If I cut back, I feel I am not getting any exercise at all. – J.E.

ANSWER: For years, the rule used to determine a person’s maximum heart rate has been to subtract the person’s age from 220. A 59-year-old’s maximum heart rate, therefore, would be 161. For a training effect on the heart, it is suggested to take between 70 percent and 85 percent of the maximum heart rate as the low and high goals of exercise intensity. For a 59-year-old, that would be 113 to 137.

This rule is a rough estimate at best. Inherent in it is the possibility of a 15-beat-per-minute error. The rule also fails to take into consideration a person’s training, weight and other heart risks – cholesterol, blood pressure, family history and smoking.

Another estimate used as a reliable guide to exercise intensity is perceived exertion. People gauge the intensity of exercise by how they feel on a scale of 6 to 20. Six is very, very light exercise; 20 is very, very hard exercise. Keeping the intensity around 12 to 13 – somewhat hard – assures heart training and not overdoing it. It sounds like you do this intuitively.

The only way to answer your question with complete assurance is to have a stress test, where you exercise to the point where your heart is beating as fast as it does when you bike. When President George W. Bush was 55, he had such a stress test. His heart rate rose to 178, 13 beats above the maximum heart rate predicted for his age.

His doctors did not tell him to limit the intensity of his exercise, but they had stress-test evidence that it was safe.

DEAR DR. DONOHUE: I am worried about my granddaughter, who is 13. She is 5 feet 3 inches tall and weighs 82 pounds. She is active in all sports and excels in them. She never gets tired of practicing or playing. I am afraid she will burn out. She is skinny and eats only pizza, fried chicken, mashed potatoes and green beans. She has not yet had a menstrual period. How can we help her? – W.G.

ANSWER: Your granddaughter’s height puts her in the middle of girls her age; her weight puts her in the lower quarter of those girls. She could stand to put on a few more pounds.

Menstruation begins anywhere between the ages of 9 and 16. Some quote the average age as 12.8; others as 13.5. A girl has to have a certain amount of body fat to menstruate – about 17 percent of her total weight. Even though she is not at an age that causes concern for not yet having periods, she should try to put on a few pounds so that when she does arrive at the proper age, she will have them.

Her diet is not the best. Appeal to your granddaughter’s love of sports to get her interested in a more balanced diet – fruits, vegetables, whole grains and a variety of meats, not just fried chicken.

As long as the girl loves what she’s doing, you don’t have to worry about her burning out.

DEAR DR. DONOHUE: I am a cross-country, high-school runner. I have a little trouble running up hills. Is it best to run with short, fast strides? – R.W.

ANSWER: This is a question for a running coach, not for me. But I found an article in Running and FitNews, the publication of the American Running Association. It dealt with hill training (November/December 2002).

The suggestion is to start up a short hill slowly and then pick up the pace so you are running as fast as you would in a dash.

For longer hills – those between a quarter- and a half-mile – run up the hill at your regular race pace or just slightly faster.

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.