DEAR DR. DONOHUE: At my high school, I play basketball and run track. Lately I’ve been getting colds, strep throat, earaches and fever. Is being this active affecting my body? – K.

DEAR DR. DONOHUE: Does exercise affect the immune system? It seems like I’m coming down with more colds this year than I did last year when I wasn’t exercising. – R.K.

ANSWER: Both writers are asking if exercise impairs the immune system and makes a person more susceptible to infections.

In the recent past, the teaching was that exhausting exercise, such as intense training for a marathon, depresses the immune system. However, moderate aerobic exercise protects a person from infections like colds. (Aerobic exercise is the kind of exercise in which large muscles are continuously working for at least 10 to 15 minutes without a break. Running, jogging, swimming and biking are aerobic exercises. Most sports are a mixture of aerobic exercise and anaerobic exercise – sprinting for short distances.) There is no great amount of scientific data that proves either statement.

Highly trained athletes often say that during the periods of peak training, they’re more apt to come down with colds. There might be a basis in fact for that observation. Intense exercise leads to the production of stress hormones like adrenaline and cortisol. Both can sap the immune system.

You can tell if you’re overdoing exercise in a couple of ways. Your pulse rate increases when you’re at rest. You feel chronically tired. You lose interest in your sport. When these things happen, it’s time to take a rest.

DEAR DR. DONOHUE: Is it dangerous to exercise with a cold? – J.M.

ANSWER: A rule to exercising with a cold goes like this: If symptoms are all above the neck – a stuffed or runny nose – it’s OK to exercise. If symptoms are below the neck – a bad cough or a fever – it’s not OK to exercise.

DEAR DR. DONOHUE: What’s the purpose of warming up? I play volleyball, and my coach insists the team warms up before practice and before a game. I think we are burning calories that we should save for actual play. I’m keeping an open mind on this until I hear from you. Can’t you get the same effect by sitting in a sauna? – M.T.

ANSWER: A warm-up serves several purposes. It increases blood flow to muscles and literally warms them up. That reduces muscle stiffness that comes with inactivity. Warm muscles move more fluidly. It increases the heart rate, which benefits the entire body. It gets nerves firing with greater rapidity, so response time is shortened.

You have to do warm-ups properly. The warm-up exercise should be done with muscles moving in the same way they move during execution of your sport. Warm-ups are done with less intensity than takes place in a game or in practice. If you want a testimonial to the benefits of warm-ups, have you ever seen a professional baseball pitcher leave the bullpen and make his way to the pitching mound without first warming up?

Sitting in a steam room or a sauna provides some usefulness to muscles, but not the same kind that actual muscle contraction does. A hot room raises body temperature. To lower temperature, the body shunts blood to the skin so that heat can radiate from the surface. Not as much blood reaches muscles as it does when they’re active.

DEAR DR. DONOHUE: Does playing during menstrual periods affect performance? – N.R.

ANSWER: Menstrual periods have little influence on performance. However, if a girl suffers from menstrual cramps, they can have a deleterious effect on performance.

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.