DEAR DR. DONOHUE: Please set the record straight. I am completely confused about how much exercise is enough. One time I heard it was half an hour. Then I heard it had to be a full hour. I know few people who can exercise for a full hour – and I can’t.

What do you say is enough exercise to get benefits from it? – R.P.

ANSWER: If people do any exercise, they get benefits from it. Many people spend less than 20 minutes in 24 hours doing any form of physical activity. Their benefits from doing five minutes of exercise would be great.

If your goal is professional athleticism, then you have to devote hours upon hours every day to exercise, the same as do people wanting to be concert pianists.

Now experts are saying that moderate amounts of exercise bring great returns when it comes to keeping the heart healthy, arteries free of buildup and blood pressure low. Golfing only three days a week is enough exercise to qualify as “moderate” exercise. (The golfer has to walk the course.) Climbing eight flights of stairs daily is also considered moderate exercise. The complete eight flights do not have to be climbed at one time. Walking 9 miles a week decreases the risk of death by 9 percent. This sort of exercise is within the capability of just about everyone.

Do you want to read an excellent exercise book? Get or take out from the library Harvey B. Simon’s book, “The No Sweat Exercise Plan.” He presents sensible exercises that are not taxing and not time-consuming but provide great health results.

DEAR DR. DONOHUE: I just found out that I am pregnant. I am and have been a dedicated exerciser. What sort of exercise is safe for me and my baby during my pregnancy? What things should I avoid or cut back on? I don’t want to get out of shape. – C.R.

ANSWER: Exercise during pregnancy provides few risks for healthy women. Exercise might benefit the fetus too. That’s not proven beyond the shadow of a doubt. It does not, however, hurt the fetus.

If a woman has been exercising regularly before she became pregnant, she can continue her program without modifications through much of her pregnancy. After the first three months of pregnancy, a woman should not spend a lot of time lying on her back on the ground while exercising. In that position, the expanding uterus presses on veins whose blood is returning to the heart. In the later months of pregnancy, the woman won’t be able to do the same amount of exercise she could do previously. She should stop any exercise that provokes vaginal bleeding, gives her a bad headache, makes her unusually short of breath or produces lasting chest pain.

Women who haven’t exercised before pregnancy should stick to moderate exercise. Walking is an example.

Women who have uncontrolled diabetes or uncontrolled high blood pressure should ask their doctors what, if any, exercise is appropriate for them.

DEAR DR. DONOHUE: Why should people warm up before exercise or before playing a sport? Can’t you warm up by just playing or plunging into your exercise routine? Does stretching count as warming up? – B.K.

ANSWER: Warming up increases muscle temperature and blood flow to muscles. That makes muscles more flexible and more adaptable to the unanticipated movements occurring in every sport. Warming up increases the speed of nerve transmission, something that’s essential for quick responses.

Playing or exercising without warming up is asking muscles to go from a resting state to a fully active state without preparing them for the transition.

Stretching is not the same as warming up.

Warm-up exercises include things like jogging in place and jumping jacks. Pitchers warm up by throwing a ball at greatly reduced speeds.

DEAR DR. DONOHUE: My son is 60 years old and suddenly came down with ulcerative colitis. He has been on steroids for several months. What causes it? Is there a cure? – C.M.

ANSWER: The colon – the last 4 or 5 feet of the digestive tract – is the site for ulcerative colitis. As the name implies, it’s a condition where the colon lining is studded with superficial ulcers – sores that resemble a very badly skinned knee.

The cause is believed to be an unwarranted assault on the colon lining by the immune system. Why? No one is sure.

Your son is not of an age when ulcerative colitis usually strikes. It usually makes itself known between the ages of 14 and 38, but it can come on at any time. Bloody diarrhea, abdominal pain, cramps before a bowel movement, fever and weight loss are some of its most prominent symptoms.

Cure? Maybe not. Control? Usually possible.

When colitis is at its worst, resting the colon by feeding the patient intravenously can calm things down.

When the process is less hectic, medicines, with the names Rowasa, Pentasa and Asacol, can usually bring things under control. If the colitis is kicking up its heels, cortisone drugs can quiet the inflammation. Prednisone is the one most often chosen. Medicines with a direct effect on the immune system are also useful. Two such medicines are azathioprine and cyclosporine. A new medicine, infliximab, has been successful for Crohn’s disease, a twin of ulcerative colitis. It is now being used for ulcerative colitis and has shown good results.

When medicines fail to control the inflammation and ulcers, surgery can put an end to the problem.

However, it is often necessary to make repeat surgical adjustments after the original operation.

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