DEAR DR. DONOHUE: I am 17, a high-school junior and a good basketball player. I would be very good if I could jump higher. Are there any muscle exercises that can turn me into a great jumper? – N.J.

ANSWER: Have you ever heard of plyometrics? They are exercises designed to increase the explosive power of muscle contractions. They are used to increase jumping height. They are also used for many other athletic skills involving both arms and legs.

One jumping plyometrics exercise is to jump onto a solid wooden (or equally sturdy) box. Begin with one that is about 12 inches (30 cm) high. From a semi-crouch position alongside the box, spring onto it. Come back down and repeat the jump five to 10 more times. When the 12-inch jump no longer presents a challenge, get a box 4 inches higher. You can keep increasing the height by 4 inches until your reach a box height of 32 inches. It takes a long while to get to that level – months and months – so don’t rush things.

A more rigorous plyometrics exercise is to jump off the box, land and then immediately jump as high as you can. Don’t let the feet stay in contact with the floor or ground for very long. Start out with a 12-inch box as above and increase the height as you get used to the drill. If this causes any foot, knee or leg pain, stop. Children under 16 shouldn’t be doing this exercise. Very heavy people should jump from only modest heights.

If you want more details on plyometrics, you can find them in “Essentials of Strength Training and Conditioning,” edited by Thomas R Baechle and Roger W. Earle and published by Human Kinetics. The librarian at your school might be able to obtain a copy of the book for you.

You must also do standard leg-muscle exercises with weights. I know your coach can give you all the information on what kinds of these exercises to do. I am sure you are already aware of them – squats, toe raises and knee extensions.

DEAR DR. DONOHUE: You wrote that weightlifters should let exercised muscles recuperate for 24 hours. I believe you mean to say 48 hours. – P.B.

ANSWER: I meant to say, and I didn’t do so clearly, that exercised muscles should not be taxed two days in a row. In other words, if you do weightlifting arm exercises on Monday, you should not do weightlifting arm exercises on Tuesday. You can do them again on Wednesday.

You said it much more clearly than I did.

DEAR DR. DONOHUE: I am a male of age 75. I am in good condition, am 5 feet 11 inches tall and weigh 170 pounds. This is my exercise program, and I wonder if it is too much. – R.L.

ANSWER: I haven’t included the details of R.L.’s program, but believe me, it is impressive and exhaustive. I can make a few generalizations about overtraining and let R.L decide for himself if he is doing too much.

An important sign of overtraining is chronic fatigue. Usually this happens to a highly competitive athlete determined to set a school or world record. It can happen to the everyday exerciser, too, and it is a universal sign of too much exercise.

A rise in the resting pulse is another marker of overtraining. If a person’s pulse, while sitting, used to be 60 and it has risen to 65 or 70, then that could be an indication that the person is going overboard with exercise. It’s a good habit for all exercisers to record their resting pulse when they wake in the morning. They should not take the pulse immediately after the alarm has sounded, but wait a minute or two to calm the heart’s response to the jarring noise of the alarm. A rise in resting pulse serves as a barometer of too much exercise.

If people are concerned about gauging the intensity of exercise while engaged in it, they can tell if they are straining too greatly if they are unable to carry on a conversation while exercising.

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.