QUESTION: I am 61, in good health, and ride a Tunturi Recumbent cycle for exercise. I have begun a daily exercise program of about 20-25 minutes and six miles. The cycle digitally monitors the speed, time, distance and pulse reading.

I try to keep my speed at about 17-19, and after a few minutes my pulse gets into the low 100s. After a short cooling down period my pulse will decrease to around 65-68. Is the pulse rate during workout high enough, or should I be pushing my body a little harder during the exercise session? Another question. Does exercise need to be sustained, or does it matter if you stop for a brief time on occasion?ANSWER: The guideline for intensity suggests working between 70 and 85 percent of your maximum heart rate. In your case, the maximum heart rate is about 159 (220 minus your age). Seventy percent of 159 is 111 and 85 percent is 135. Using these guidelines, you should work at a heart rate somewhere between 111 and 135.

The problem with using these guidelines is that they are averages from the general population and the standard deviation for predicted maximal heart rate within the age group is about plus or minus 10 beats per minute. Thus, the maximum heart rate will be overestimated for some people and underestimated for others.

Because of this variation in predicting maximum heart rate, you have to be careful not to get too hung up about the heart rate you use during exercise - the predicted values may be either too high or too low for you.

A better system, in my view, relates to how you feel during the exercise bout. If you are breathing rather hard, if you are sweating moderately, and you feel fairly tired when you get through, you are probably using the proper intensity no matter what the heart rate is during the work bout. You really shouldn't have to "push" the body during a normal workout unless you are working at such a low level that none of the signs of work mentioned above are being noticed.

The last question related to whether or not exercise needed to be sustained to be effective. There does seem to be an exercise duration threshold of about 15 minutes. Exercise done for less than this minimum will probably be less effective for making measurable changes than exercise carried on for a longer time.

However, many athletes train their cardiovascular system using a technique called interval training, where they do several work bouts at high intensities with short periods of rest (usually active rest) between.

I think your program is just about perfect for you.