DEAR DR. DONOHUE: I am a 58-year-old male, and I’ve been taking atenolol to control my blood pressure for about five years. I notice that when I work out on a stationary bike less than 12 hours after taking my medicine, I can reach a difficulty level of only six, and I can get my heart rate up to only 120 beats a minute. However, if I work out 26 hours after taking my medicine, I can reach level 8, and my heart rate will be in the 150 beats a minute range. I wonder if the lower level of workout is beneficial. — M.P.

ANSWER: Atenolol (Tenormin) is one of the many beta-blocking medicines. High blood pressure, prevention of a second heart attack and slowing the heartbeat are some of the reasons why it’s prescribed.

When on a beta-blocker, people are not able to use heartbeat (pulse) as an indication of exercise intensity. You’ve proven this. Your heartbeat reaches a higher level when you have not taken your medicine for one full day, and its effects have worn off. You are trying to use heartbeat as an indication that you have reached your “training zone.” Atenolol slows your heart, so heart rate can’t be way to judge how hard you are exercising.

You can use an equally valid criterion, perceived exertion. You judge how hard you are exercising by what your body tells you. If you feel you are working “somewhat hard,” you are at a level of exertion that’s the equivalent of a heart rate of 120 to 130 beats a minute. That’s a beneficial heart rate, one that’s safe. If you determine that you’re exercising “hard,” you’re exercising at a level of a heart rate of 140 to 150 beats a minute. That exercise intensity warrants approval from your doctor.

Heart rate cannot be used as a determinant of exercise strenuousness for all sports. In swimming, including speed swimming, the heart will not reach the same pace it reaches when doing the equivalent amount of exercise on land. Cool water, the horizontal position of the swimmer and the buoyancy of water result in a slower heartbeat even though exercise intensity is the same as it is on firm ground.

DEAR DR. DONOHUE: I am responding to the letter from a woman who is the grandmother of an 11-year-old boy doing tae kwon do.

I began tae kwon do at age 67. I have advanced through the ranks to achieve the rank of black belt. I will be 75 my next birthday and continue to train in tae kwon do. My twin grandchildren began training at age 4 and achieved the rank of junior black belt. I assist training young children in my school. These youngsters are 4 years old into their teens. I am not aware of any injuries to any student. A highly qualified instructor brings strict control to training and prevents injury. A serious student learns respect, courtesy and discipline. — L.S.

ANSWER: Thank you. I’m sure the boy’s grandmother appreciates you input.

DEAR DR. DONOHUE: I am a 48-year-old man, 5 feet 8 inches and 155 pounds. I read your advice on challenging your fitness to encourage growth and so on.

I’d like to comment on those of us who just want to maintain our fitness rather than build on it. For example, I jog three times a week for 20 minutes for heart health. On the other days, I knock out some push-ups and curls for upper-body physique.

Is my time and effort really worth it? — J.F.

ANSWER: Yes, your efforts are worth it. You’ve stabilized your weight, and you perform both aerobic and strength exercise. Stick with it.

DEAR DR. DONOHUE: I am 29. After my fifth child, I wanted to get back into shape by walking 60 minutes at 4 miles per hour. In the last year I’ve started jogging (6 to 6.5 miles per hour) for half an hour and walk the other half. How much more do I gain by the jog/walk? Is there a significant difference in calories burned? — D.N.

ANSWER: For a 123-pound woman, walking at 4 miles/hour burns 5.4 calories a minute, 324 calories an hour. Jogging at 6 miles/hour burns 15 calories a minute, 900 calories an hour. The jog/walk program burns a significantly greater number of calories than only walking. (I made up your weight.)

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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