DEAR DR. DONOHUE: My daughter is the best swimmer on her school’s team. Last season, she developed shoulder pain and was sidelined for the final month and a half. We don’t want a repeat. Are there any exercises she could do to keep her shoulders healthy this year? – R.M.

ANSWER: A swimmer who practices two hours a day can rack up more than 4,000 swimming strokes daily. If that swimmer practices 200 days a year, he or she is doing about a million strokes yearly. That’s a lot of stress on the shoulders, and overuse of the shoulders is the most common cause of swimmers’ shoulder pain.

Your daughter’s coach should analyze her stroke technique to see if she’s making any motions that are placing additional stress on the shoulders. I am told that swimmers who breathe only on one side overburden the shoulder on that side.

Furthermore, swimming overdevelops the front chest muscles and certain shoulder muscles. Muscle imbalance adds to shoulder problems.

One good exercise for correcting muscle imbalance is the following one. Your daughter should lie on one side with her head supported in the hand on the downward side. With the other hand, she grasps a lightweight dumbbell – 1 or 2 pounds – in such a way that her palm faces inward toward her body. The dumbbell is close to her abdomen, and the elbow is bent 90 degrees. She should raise the elbow an inch or two above her side. Then she turns her arm to lift the dumbbell upward as far as comfortable and holds the lifted position for five seconds. When she can do three sets of 10 repetitions with a rest break between sets, she can increase the weight by 1 pound. She should exercise both shoulders in this way.

DEAR DR. DONOHUE: This question is in reference to a healthy female adult and assumes she is receiving sufficient nutrition. What is the minimum amount of aerobic exercise necessary to maintain optimum bone and cardiovascular health? Is there a level that is considered too much?

My sister and I have a running (no pun intended) argument about this subject. – Tired of This Discussion

ANSWER: In 1995, the edict went out that 30 minutes of aerobic exercise on most, if not all, days of the week would bring the greatest benefit to cardiovascular health. The 30 minutes can be broken into two 15-minute sessions or three 10-minute sessions. Aerobic exercise is the kind of exercise where large muscles are working nonstop – jogging, walking, swimming, biking, leaf-raking. The new recommendations are for an hour of exercise. That’s a bit much for me. If you have the time and energy to do an hour, so much the better. Even if you don’t have the time and energy to do 30 minutes, any amount of exercise is better than no exercise.

For bone health, weight-bearing exercise is necessary. Walking, jogging and running qualify as weight-bearing – the skeleton holds up the body’s weight during the exercise. Even better for bones is resistance exercise – lifting weights. Getting in 20 to 25 minutes of resistance exercise three days a week keeps bones healthy. The days should not be consecutive days if you are exercising the same muscles.

DEAR DR. DONOHUE: I have a question. I have limited use of my right ankle due to arthritis. Instead of walking, I use a stationary bicycle and would like to know how to compare the benefits of a stationary bike with walking. How do they compare? – J.B.

ANSWER: To compare these two activities, a number of variables have to be taken into consideration. The energy cost of walking depends on people’s weight, how fast they walk, the incline of the terrain, the surface walked on, and climate factors like wind and cold weather.

In stationary biking, pedaling speed and the setting that determines the force needed to turn the pedals must be factored in to estimate the energy consumption of the biker.

Pedaling with light effort on a stationary bike burns about the same number of calories that walking at three miles an hour does.

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.