DEAR DR. DONOHUE: I am a 50-year-old female and do resistance training several times a week to ward off osteoporosis. Does the entire skeletal system strengthen from weight training regardless of the muscles used, or are only the bones involved in the exercise benefiting from it? Do you recommend specific exercises for the hips and spine? – G.M.

ANSWER: Exercise stimulates bone growth when muscles pull on bones. The pull prods bone-building cells to get to work. In answer to your question, only the bones tugged on by muscles receive the osteoporosis benefits of the exercise. That needs further explanation.

Weight-bearing exercises are good for bone-strengthening. Those are exercises in which body weight is supported by the skeleton. Jogging, stair-climbing and playing running sports like tennis are considered weight-bearing. Walking is a weight-bearing exercise, but it is not as good an osteoporosis treatment as is jogging. In jogging, the impact of foot on ground produces a greater force on bones than the force that comes from taking a walking step. Walkers can get more benefit if they occasionally break into a jog or if they carry a backpack with even a light weight in it.

Resistance exercise is the best exercise for bone-building. Resistance exercise is lifting weights. If a person does only arm-muscle resistance exercise, only arm and shoulder bones are getting the major benefits. However, just about all weightlifting exercises require the involvement of other body sites – back, hips and legs – to stabilize the body and to assist in lifting the weight. Those bones derive some gains from arm exercises. It is better to have a comprehensive weightlifting program, one that involves all body muscles – arms, shoulders, back, abdomen, hips and legs. Of course, specific exercises for the hips and back will provide more benefit for those areas. The amount of weight lifted does not have to be huge. Starting out with even 1 pound is enough to see results. However, there should be a slow but progressive increase in the amount of weight lifted.

DEAR DR. DONOHUE: Hello. I am a 16-year-old boy, 5 feet 8 inches tall and weighing 138 pounds. I am on the high-school wrestling team and work out regularly. I have gotten really serious about working out in the past year. Recently I decided to take creatine. After I took it for two days, my mom said she noticed a change in my personality. (My personality has not changed. I have always had a low tolerance for interference.) She wants to know the side effects of creatine. Can you help me? After two days I have noticed an increase in my strength. – Anon.

ANSWER: Creatine, a substance found in muscle, has become a popular supplement for athletes. There is evidence it works for building muscle, but don’t expect breathtaking breakthroughs.

How it works is a bit foggy. Since creatine is involved with energy production, it might enhance muscles’ energy supply and enable a person to lift heavier weight more times.

Most users have no side effects. Muscle cramps, diarrhea and weight gain have been reported as being possible side effects. An occasional article addresses the possibility of kidney damage from its use, but proof of that is not great. Stay within the manufacturer’s recommended dose and you shouldn’t run into trouble.

Tell your mom that I cannot find a single reference that creatine causes any personality changes. You could, along with building your muscles, build your tolerance for interference. Your mother will be greatly pleased by this side effect.

You think it made a difference in your strength in two days? I don’t know about that, but if it makes you happy to believe it, stick with the belief.

DEAR DR. DONOHUE: I am 66 years old and swim for two hours three times a week. After about one hour I begin to feel a chill, even though the water temperature is 82 F. Am I burning more calories to stay warm, or should I get out of the water after an hour? – B.S.

ANSWER: When the body warms itself, it’s burning more calories. I don’t know why this is happening. Are you exhausted after an hour? That might bring on the chill. For me, get out of the pool, take a rest, and then get back in. Let me know the result.

DEAR DR. DONOHUE: Please explain reflex sympathetic dystrophy. A family member broke her foot five months ago, and it is still not better. RSD is her doctor’s diagnosis. – S.M.

ANSWER: Reflex sympathetic dystrophy, now known as complex regional pain syndrome, is a difficult problem for patients and their doctors. It’s a mysterious reaction to trauma. Broken bones, sprains, strokes, heart attacks and even a minor bump can produce it. It’s persistent pain and tissue wasting (dystrophy) long after the injury has healed.

Previously, doctors believed it was due to an abnormal response of the sympathetic – hence the old name – nervous system to the trauma. The sympathetic nervous system is the part of the nervous system not under voluntary control, and it’s responsible for such things as the expansion and constriction of arteries.

What actually transpires is not clear, but about three months after a traumatic event, like a broken foot, the skin over the traumatized area reddens and warms, the surrounding tissues swell, and pain there is severe.

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.