DEAR DR. DONOHUE: Where can I find an archive of your previous columns? I’m trying to locate an item about improving vertical leap for high-school athletes. – J.H.

ANSWER: As far as I know, there are no Donohue archives, but I’ll repeat the plyometric piece for you. It’s still basketball and volleyball season, and all young athletes want to learn how to jump higher.

Plyometrics is training for explosive power. It’s not restricted to jumping, but jumping is one of its most popular applications.

One plyometric exercise is depth jumping. The athlete jumps off a sturdily constructed box or platform and, immediately upon landing, he or she jumps up as high as possible – very little delay between foot contact with the ground and the upward jump.

Plyometric jumping is hard on joints, ligaments and tendons, so it should be used in moderation. Prepubertal children shouldn’t engage in it. Anyone weighing more than 220 pounds should not be allowed to jump from a height greater than 18 inches (45 cm). Jumpers should have sufficient leg strength. They ought to be able to squat with a load of about 1.5 times body weight.

Start with a box or platform that is 12 inches (30 cm) high. The athlete jumps off the box onto grass or a rubber mat and then immediately propels him-or herself upward after ground contact. At first, two sets of five consecutive jumps are enough. With time, that can be extended to three sets of eight to 10 jumps. The height of the box or platform can be gradually increased in increments of four inches (10 cm). The height should not exceed 42 inches (106 cm).

If no box or platform is available, plyometric jumps can be done from a squatting position on the ground. From that position, the jumper jumps as high as possible, doing the same number of sets and repetitions.

DEAR DR. DONOHUE: In a recent article you said that exercise such as walking, running and housework prolongs life. What about weightlifting? Is that as beneficial? – O.L.

ANSWER: Weightlifting has many benefits. It builds muscle and bone strength, gets rid of fat and lessens the chances of joint, bone and muscle injury. It isn’t, however, aerobic exercise. Aerobic exercise is the kind of exercise in which large muscles are continuously moving for 20 to 30 minutes with no rest periods. The heart reaches a target heart rate and remains at that heart rate for the duration of the exercise. Aerobics is the kind of exercise that’s designed for heart health.

Weightlifting can be turned into an aerobic exercise if the lifter doesn’t take long breaks. He or she can quickly move from an arm exercise to a leg exercise and then back to the arm exercise without much of a pause between exercises. By changing exercises, the lifter gives one set of muscles a chance to recover but still keeps the heart beating at a target rate.

DEAR DR. DONOHUE: I am 12 years old, and my brother says that if you pop your toes enough, it will weaken the bones. Is this statement true? – I.D.

ANSWER: I.D., I have to acknowledge my ignorance. I don’t know what toe popping is. How about describing it for me, and I’ll give you an answer? And what bones do you mean? All, or just toe bones?

DEAR DR. DONOHUE: I have a stationary bike with only a speedometer and a mileage gauge. Is there any benefit from using this bike for exercise? How many miles a day should I spend on it? – L.H.

ANSWER: You can get plenty of exercise from a stationary bike. You should exercise for 30 minutes a day, but you can break the exercise into three 10-minute sessions if you want.

Pedal with enough speed to get your heart to its training zone. Subtract your age from 220 and then take 60 percent to 75 percent of that number to bracket your lower and upper training heart-rate zone. I don’t know your age, but if you are getting on in years, check with your doctor to see if such exercise is safe for you.

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.

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