Dr. W, on Debunking the Gospel
In medicine you frequently read something, learn it, practice it and then pass it on and teach it. Much of medicine is assumedly correct and accepted as Gospel. Take maximum predicted heart rate (MPHR) as a guideline for fitness and clinical use in exercise stress testing. Doctors prescribe exercise programs with the goal of reaching and maintaining 65- 75 percent of MPHR for endurance training and brief intervals of 80-90 percent for improving capacity. We calculate MPHR on the basic formula of 220 minus your age. How did this all come about?
Years ago, I read this wonderful article in the NY Times that described the problems of accepting this calculation and how it was hatched. In short, the formula was devised by Dr. William Haskell Ph.D. and Dr. Samuel Fox director of the federal Public Health Service for heart disease. They were sitting on an airplane on their way to a medical meeting and Dr. Fox, after reviewing some data on a small group of patients which is not representative of the general population, came up with the above formula. I suppose you can call it flight science. He never expected it to take off and be used by everyone as a way of predicting MPHR. This formula would become the basic formula for Polar heart rate monitors, all exercise machines and guideline used in exercise stress testing. If a patient would reach 90-100 percent of MPHR they would stop the test. The gold standard.
Subsequent studies, using a much larger data base (18,700 people with a wide patient representation), showed that the formula under predicted MPHR especially in older people by as much as 20 percent. So much for relying on a common accepted value. (For those interested, a more accurate formula to predict MPHR is 208 – 0.7 x age.) Even using the new formula there can be a wide range of maximum heart rates in individuals. Some people will reach a heart rate of 150 beats per minute (BPM) for a certain activity while others will go up to 200 BPM. In fact, people respond differently to exercise with some pumping out or ejecting a larger amount of blood with a slow heart rate and others by racing their hearts.
Clinically, in performing an exercise test the goal is to reach 80-90 of MPHR to improve the accuracy and specificity of the exam. Interestingly, when evaluating for heart disease it may be less important to see how high your heart goes than to see how quickly the heart drops with cessation of exercise. An average person’s heart rate drops by 20 beats in a minute post exercise while an athlete’s rate can go down by as much as 50 beats in a minute. Those whose heart rates drop slower than 12 per minute have a higher incidence of heart disease.
Enough of the science and clinical relevance. Let’s talk about you and me. What does the lay person make of this information? Perhaps, too much emphasis is placed on obtaining a certain heart rate during exercise. Sure, if you are training for that marathon you want to obtain and maintain a heart rate that will improve your endurance. For the routine exerciser what is most important is doing that 30- 45 minute workout program 5X per week or even daily. Driving the heart up from baseline and sustaining it for a period is where you reap the benefit. That is why some people even suggest one or two minutes at peak maximum effort per day to obtain a positive cardiovascular effect. The goal is to raise heart above baseline for a sustained period. You have 8-10 flights in your apartment building? Then do it once a day. Is your office on the 6th floor? Climb it. Want to do the gym? That’s cool. 30-45 minutes on a treadmill at a reasonable pace will do the trick. Skip the monitor and the tracker. Simply exercise as often as you can.
Next time we look at body and abdominal fat.