DEAR DR. DONOHUE: I’m a beginner marathon runner. I have run one, and that was last year. About halfway through the race, I began to have stomach cramps – not so bad that I had to stop, but bad enough that I had to slow down for about 15 minutes. I plan to run another marathon this year, and I’d like to do it without cramps. How do I go about that? – R.N.

ANSWER: Long-distance runners often suffer from digestive-tract upsets, and stomach cramps are one of those upsets. The explanation has to do with the diversion of blood from the intestines to the leg muscles. The gastrointestinal tract makes its displeasure known by cramping up – and in other ways, like diarrhea, for some.

You ought to start training six months to a year before the actual event. Are you running distances that approach marathon mileage (26.2 miles, 42.2 kilometers)? Part of that training is running distances greater than 16 miles and gradually increasing the distance to 20 to 22 miles. You can’t expect to run these long distances every day. You’ve got to give your body a chance to recover. In the two weeks before the race, don’t run such long distances. You’ll retain your level of training by running a more reasonable number of miles. However, getting your body adapted to long runs will make your digestive tract immune to them.

During long runs, keep yourself hydrated. Drink water with some salt in it, or drink commercial sports drinks. You have to replenish not just water but also sodium during long runs, especially long runs in hot weather.

On race day, eat at least three hours before the marathon starts. The meal should be one that’s composed mostly of carbohydrates – pancakes, for instance. Carbohydrates leave the stomach more quickly than fats or protein.

In the days before the race, stay away from gas-producing foods: beans, onions, peas, corn, broccoli, apples, peaches and bagels, to mention a few. Stop dairy products. For some people, they create havoc in their digestive tract.

Let me know where the race is going to be. I’ll wave to you. Don’t enter my name, please.

DEAR DR. DONOHUE: I am a 73-year-old male, 5 feet 10 inches tall and weighing 170 pounds. My exercise program (five days a week) is: stretching for two minutes, deep breathing, 300 sit-ups in which the shoulder blades clear the floor done in intervals of 100, and then 300 push-ups in intervals of 100.

Then I am on a treadmill for 90 minutes, at a speed of 2.9 miles an hour, and at an incline of 9 percent.

I don’t meet the requirement of walking at a speed of 15 minutes per mile – 4 miles an hour. Does the 9 percent incline compensate for not reaching that standard? – J.W.

ANSWER: Forget the standard. You’re doing more than enough exercise.

Your body tells you if the intensity of exercise is as strenuous as it needs to be. If your pace on the treadmill feels somewhat difficult, then that’s as fast as it has to be. Perceived exertion is as good a criterion for exercise benefit as heart rate or theoretical statements about how fast you should walk.

The incline does compensate for the reduction in speed. Walking speeds are given for level surfaces. An incline makes the walk much more difficult.

DEAR DR. DONOHUE: I am a 68-year-old woman who walks five miles a day, and I use a pedometer when I walk. I realize I need to do upper-body strength work, but are the five miles enough for my lower body? – M.G.

ANSWER: Strength exercise consists in lifting weights. When walking, you’re lifting body weight with each step, and it’s the legs that are doing the lifting. So, yes, it qualifies as lower-body strength work. One element of strength training is to progressively challenge the muscles with more weight to keep muscles growing larger and stronger. You can do that by walking with a backpack. Once you get used to the empty pack, you can put some weight in it, starting with 1 pound.

DEAR DR. DONOHUE: I would appreciate your comments on mycosis fungoides. Is there any treatment? Does it affect inner organs? – B.M.

ANSWER: Mycosis fungoides is a rare cancer in which lymphocytes – one variety of white blood cells – have turned cancerous and penetrate the skin to form flat patches, often red or brown, that can be quite itchy.

The cancer usually progresses slowly. The patches evolve into raised patches and then into raised clumps that frequently ulcerate.

Cancerous lymphocytes, in time, can invade lymph nodes, lung, spleen and liver.

One treatment involves spreading cortisone creams or ointments on the involved skin. Nitrogen mustard applied in the same way is another treatment.

Radiation and chemotherapy are sometimes used.

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