DEAR DR. DONOHUE: Can you help me get back on my bike? I love biking, and it gives me a chance to exercise in a way that suits me. However, after about a week of biking, I get knee and back pain. Am I doing something wrong? Any information will be appreciated. – G.S.

ANSWER: It could be that a few simple adjustments to your bike will end your knee and back pain.

When the foot is in the bottom position with the pedal at 6 o’clock, the knee of that leg should have a slight bend. If you want to be exact, the knee should be bent to 30 degrees. If the seat is too low and the knee bends more than that, there’s a great deal of compression on the knee, and it brings knee pain. The pain is felt in the front of the knee. If the seat is too high and the knee has no bend, that position brings on pain in the back of the knee. You can estimate the height of the seat by multiplying your inseam measurement by 1.09.

Knee pain also can come from overuse – too much time spent biking, biking too great distances or not giving your knees enough rest between biking sessions. Start out modestly, with periods of 10 minutes or fewer, and bike only three times a week. Each week add a few more minutes. You also can gradually increase the biking days until you are biking seven days a week, if that’s what you want.

Back pain often can be traced to leaning too low and too far forward, like the pros do. You don’t have to assume the extreme crouched position taken by professional cyclists. Sit more upright. Adjust the handlebars so that they’re at lease six inches higher than the seat.

Bon voyage.

DEAR DR. DONOHUE: How is the calorie cost of each exercise obtained? I ask because I have consulted many calorie charts, and I get different values from each one. How do you know which is more accurate? I’m trying to lose weight, and this means something to me. – K.C.

ANSWER: The direct estimation of the calorie-burning of individual exercises is determined by putting an exerciser in an insulated room that has water in copper tubes. The heat generated by the exerciser raises the water’s temperature, and that gives the number of calories generated. This is a cumbersome and tedious method.

Most calorie estimates are made by measuring the amount of oxygen an exerciser consumes and the amount of carbon dioxide he produces. Equations can turn that information into calorie production. This is a much easier method for determining the calorie cost of individual exercises.

Charts are good, but they don’t agree. It’s impossible to design a chart that gives reliable information for everyone. Calorie-burning depends on weight, sex, body composition, characteristics of the terrain, wind resistance and a host of other factors. You can use just about any calorie chart for a rough estimate of what you’re burning.

The calories in food are determined by other methods.

DEAR DR. DONOHUE: I have a low resting heart rate of around 45 to 55 beats a minute. I do a lot of biking and go 60 to 70 miles a week. My heart rate, while biking, gets up to about 90 beats a minutes. Is there something wrong with this? I always had a low heartbeat.

A few years ago I had a stress test and was told that I had the heart of an athlete and should not worry about the slow rate. Now a doctor tells me it may be too low. Do I have something to worry about? – L.Y.

ANSWER: You have two questions. Is your resting heart rate an indication of bad health? Is your exercise heart rate high enough to benefit your heart?

A resting heart rate of 60 to 100 beats a minute is considered normal. Trained athletes have slower heart rates because their hearts pump more blood with each beat than the untrained heart. I believe you fit in this category.

Your exercise heart rate doesn’t reach the levels it should for the same reason. However, it’s twice the beating speed of your resting heartbeat, and that’s more than enough to benefit your heart.

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

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