DEAR DR. DONOHUE: I begged my husband not to do it, but he went ahead and bought our 10-year-old son a set of barbells and dumbbells for Christmas. I think that 10 is far too young to be exercising with weights, and I have heard it can stunt a child’s growth and cause other problems. What’s the official word on this? – C.B.

ANSWER: It used to be taught that weightlifting for children who had not reached puberty was a waste of time. Since there is not a large supply of male hormone before puberty and since muscle growth is dependent to a large extent on male hormone, weightlifting at this stage in life would be futile.

Furthermore, people cited the danger children could face from injuring their growth plates. The bones of growing children have areas of cartilage. Those areas are growth plates. They permit bones to grow longer. Growth plates are also areas of relative weakness compared with the rest of the bone.

Putting stress on growth plates can lead to injury. However, weightlifting doesn’t stop growth unless the growth plate is disrupted by an injury. Such injuries are most uncommon.

Nowadays, experts in growth, development and exercise encourage pre-pubescent children to lift weights. The relative lack of male hormone doesn’t mean that there won’t be any muscle growth. The growth just won’t be as exuberant as it will be when male hormones kick in.

If your husband supervises your son’s exercise, then barbells and dumbbells are going to work to your son’s advantage. Your husband has to emphasize proper technique in lifting, and he must discourage the boy from trying to lift heavy weights. A heavy weight is one that the boy cannot lift with ease and with proper form at least eight times in a row.

The exercise will make the boy stronger. It will also teach him balance and coordination, things that will serve him in good stead regardless of his athletic inclinations.

DEAR DR. DONOHUE: What’s the advantage of doing bench presses with the back half of the bench raised? I see lots of people doing this in the gym where I work out. I have asked a few, and no one gives me a good answer. I am looking to you to provide one. – R.P.

ANSWER: The bench press is the exercise done while lying on a bench with a barbell resting at chest level or on the chest. The barbell is lifted straight up and then slowly returned to the starting position.

The bench press is a standard exercise for the chest wall muscles as well as for shoulder muscles and for the muscles on the backs of the upper arms (the triceps).

Your question is a good one. It makes a point that few people appreciate. A slight variation in the way an exercise is performed has a profound effect on what muscles are being exercised.

Raising the back of the bench shifts the stress of the exercise to the front shoulder muscles (the anterior deltoids).

Another example of how to change the impact of an exercise with a slight alteration of form is to perform a standard bench press holding the barbell with the hands close together or farther apart. When the hands are close to each other, the chest muscles toward the center of the chest get a greater workout; when the hands are farther apart, the outer chest muscles are the ones that are working harder.

DEAR DR. DONOHUE: What do you think of taking a handful of sugar cubes before exercise to provide extra energy? I have tried it a couple of times, and I have been surprised at how much greater my endurance is. Others say that it’s a purely psychological effect. Is there any basis to this? – B.K.

ANSWER: I don’t think so.

Sugar passes into the blood quickly, and the blood sugar level soars. That prompts a release of insulin to bring blood sugar down. Often the release is excessive, and it drives blood sugar lower than it was.

I don’t know anyone who agrees that pure sugar before exercise increases endurance.

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.