DEAR DR. DONOHUE: Our family has a summer cottage on a beautiful lake. My son and I love to fish, but this year he has turned into a swimmer and is turning me into one too. All the kids his age who come here are excellent swimmers, and he has become very good. He wants to try out for his school’s swim team. He asked me to ask you some questions. Is swimming a really good body conditioner and muscle builder? What’s drag? Why do swimmers shave their bodies? How does water temperature affect a swimmer? And I have added one of my own: Do I aim for the same heart rate when swimming as I do when running? – D.D.

ANSWER: These are questions better asked of your son’s future swimming coach, but I’ll have a go at them.

Swimming is an excellent conditioner. It builds both upper- and lower-body muscles. All the swimmers I have seen have huge shoulders. Swimming is a great aerobic activity, one that is excellent for the heart. It’s said that the energy cost of swimming is four times the energy cost of running the same distance. That, of course, depends on how fast a person swims or runs.

Swimmers shave off body hair to diminish drag. Drag is a force that works against a swimmer in propelling the body forward. Friction occurs when water runs over the body, and hair on the skin creates more friction than smooth skin. If you have noticed, some swimmers are wearing whole-body suits. Those suits are supposed to cut down on drag too.

Cold water ups the energy cost of swimming. The body has to burn fuel to maintain normal body temperature. The ideal water temperature is between 82 and 86 F (28 and 30 C). At a water temperature less than 77 (25), the body is fighting hard to conserve heat.

The training-zone heart rate during swimming is 10 to 20 beats slower than the training-zone heart rate during dry-land exercise.

DEAR DR. DONOHUE: I am a 59-year-old male and a double amputee (both legs). My length is 4 feet 7 inches, and I weigh 180 pounds. My sitting heart rate is 78, and it has always been high.

My question is what numbers do I use for my exercise program? Do I make any adjustment in the heart rate because I have no legs? – C.M.

ANSWER: Let me admit I could find no references that address this question. My guess is your target heart rate should be the same as the target heart rate of a person with legs. Height hasn’t anything to do with figuring the optimum heart rate. Age does.

You deduct your age from 220 and then take 65 percent to 80 percent of that number to determine your heart rate training zone.

Upper-body exercise (arms and shoulders) is more demanding than lower-body exercise (legs). I don’t know what kind of exercise you do, but you shouldn’t have trouble attaining an appropriate heart rate.

Why do you say a resting heart rate of 78 is high? It’s not. The normal resting heart rate ranges from 60 to 100 beats a minute.

DEAR DR. DONOHUE: Your recent article on body mass index – BMI – was interesting and informative. However, I have an alternative method for measuring BMI. My method is to remove all clothing and look in the mirror. Your BMI will be written on your face. What is your opinion? – G.H.

ANSWER: My opinion is that your method beats the arithmetic method of estimating BMI. I like it a lot. I’ll push for its adaptation by everyone.

DEAR DR. DONOHUE: I have had type 2 diabetes for more than 10 years. I can control it by watching what I eat. When I was first diagnosed, I was overweight, and I lost 50 pounds.

I have several friends who also have type 2 diabetes, and they are on medicine for it. They say that by taking medicine, they don’t have to watch what they eat. Is this true?

ANSWER: The best way to control any illness is to treat it without medicine whenever possible. All medicines have side effects.

Diet is an important aspect of diabetes control. Since weight loss and a diabetic diet have kept your blood sugar in check, stick with them. Only if diet and weight loss cannot bring blood sugar to acceptable levels should a person have to resort to medicine. In point of fact, that happens often enough.

Your friends don’t have free rein to eat whatever they want. They need to speak with a dietitian about a diabetic diet.

Diabetes is becoming an epidemic disease. The booklet on this illness discusses its many facets and its treatment. Readers can order a copy by writing: Dr. Donohue – No. 402, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: As a child, my mother made me drink eight glasses of water every day. She said water flushed out poisons. Does it? – B.D.

ANSWER: No, it doesn’t. The average, healthy person can let thirst be the guide to the need for fluid. All fluids count, not just water.

I am positive I will hear from people who say I should mention the diuretic effect of some fluids, but there actually is a net gain of fluid to the body even from drinks that encourage urine production.

DEAR DR. DONOHUE: When one loses weight, is the fat loss removed through elimination processes, or what? Does it just drop off? – P.H.

ANSWER: Fat is burned to produce energy and heat, just like gas heats a house. Some of the fat-burning process generates carbon dioxide, which is exhaled. Other waste products are eliminated by the kidneys. It’s all done very discreetly.

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