DEAR DR. DONOHUE: I am a 78-year-old man. I think I am in good shape. However, I have an aortic aneurysm. I did not ask my doctor about exercising, and I won’t see him for several months. I walk and jog almost every day. I lift 10-pound weights. I am worried that this might cause the aneurysm to burst. There must be many others worried about this too. Is exercise harmful to people with aneurysms? – R.P.

ANSWER: An aneurysm is a bulge in an artery. It represents a weak spot. The danger lies in the possibility of this weak spot breaking open, with catastrophic bleeding.

The aorta is the body’s largest artery, extending from the heart to the bottom of the abdomen. Most aortic aneurysms are in the abdominal section of this artery, and I am confining my remarks to those bulges.

People with aneurysms must keep their blood pressure in the normal range. High blood pressure puts stress on the walls of arteries. Stress on a weak spot increases the risk of it bursting. Some exercises transiently raise blood pressure to high levels. Exercises during which a person strains are examples. Therefore, people with aneurysms should not lift heavy loads. What’s a heavy load? Anything that requires moderate to great exertion.

Brisk walking and jogging can be safely done. Such exercise is encouraged.

What determines the amount and degree of exercise is the size of a person’s aneurysm and the rate it grows each year. Your doctor has that information. You must rely on him or her to give you the final word on what kind of exercise is appropriate for you. Even though you’re not scheduled to see the doctor for some months, you can use the telephone.

DEAR DR. DONOHUE: I read a blurb about water exercise that really caught my attention. I have arthritis in both knees and have had to give up running. I want to stay in shape. I don’t swim, and I hate pedaling a bike. This water exercise sounds like the right thing for me.

How do I go about it? Do I exercise in shallow or deep water? I have year-round access to a pool. – L.R.

ANSWER: Many organizations sponsor classes in water aerobics. Look around, and I bet you can find such a class.

If you want to do it on your own, that’s fine too. You exercise in water that comes to about midchest level or in deep water. In midchest water, you might want to wear shoes made for such exercises. You can find them at any sporting-goods store. In deep water, you need a flotation belt that keeps you vertical.

Jog in water just as you would jog on land. Don’t expect your heart to beat as fast as it does when running on land. Even at a slower rate, you’re benefiting your heart, you’re keeping your blood pressure low, you’re burning calories and you’re saving your knees thanks to water buoyancy.

DEAR DR. DONOHUE: I oversee the weight room at our local high school. One of the athletes asked me why his breath had what he called a metallic odor to it after his last repetition on his third set. Can you tell us why this happens? – J.R.

DEAR DR. DONOHUE: Your column titled “Runner Gets Stress Fracture” reminded me of my son’s problems with stress fractures when he was in high school. He participated in both regular track and cross-country track. He had three stress fractures, including the upper and lower leg bones. He was finally fitted with orthotics and never had any additional problems, though he continued to run in high school and through college. – F.H.

ANSWER: Stress fractures are minute breaks in the bone that come from overuse and too little rest. Orthotics are shoe inserts. Often they are specially fashioned for a special problem, like an anatomical misalignment. Your son’s story provides a nice way of preventing stress fractures for some athletes.

ANSWER: My apologies to you and to the athlete. I haven’t a clue. I know that I will get an answer from readers and, when I do, I’ll let you know.

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