Here is a nice article explaining about Maximum Heart Rate. I can measure it more accurately with my new Garmin Forerunner 305 Watch ..
http://www.sportsdoctor.com/articles/heart_rate.html
Q: I do aerobic dance and have often heard my instructors say that if your heart rate goes over your maximum training rate - 90 percent of your maximum heart rate - you start burning heart muscle. What does this really mean, and what are the short- and long-term effects of this happening?
Also, on occasion, someone will exceed what is supposed to be their maximum heart rate, to which the automatic response is "you're dead." What does "maximum heart rate" really mean, how can a person go over their maximum (without dying!), and what are the implications of going over? C.B. Minneapolis, MN
A: It is extremely difficult, if not impossible, to damage a healthy heart with exercise. You do not burn or otherwise damage healthy heart muscle by exceeding 90 percent of your estimated maximum heart rate (MHR). Otherwise, there would be many more elite athletes, who daily push their heart rate to extremes, suffering heart damage.
Your true MHR is the highest pulse rate you can attain during all-out effort, so by definition, it is impossible to exceed this limit. Your MHR is most accurately determined during an exercise stress test, when you run on a treadmill and are connected to an electrocardiogram that measures your pulse during maximal exertion, The easy way to estimate your MHR is to subtract your age from 220.
But this is only an estimate. Because we are all unique human beings of different ages and levels of fitness, our maximum heart rates can vary considerably. As we get older, our maximum heart rate slows down.
Also, regular training has the effect of lowering your maximum heart rate, as well as your resting heart rate. This is because your heart, like other muscles you exercise, becomes stronger and more efficient, pumping a greater volume of blood with each beat.
How can you effectively improve your cardiovascular fitness?
Exercise also increases blood flow and develops the arterial supply to the heart. Because heart attacks are caused by inadequate blood flow to the heart muscle, regular exercise of a healthy heart is almost a sure preventive of a heart attack.
To effectively improve your cardiovascular fitness you must exercise a minimum of three times a week, 30 minutes a day at 60 to 90 percent of your maximum heart rate.
This is the basic fundamental of aerobic conditioning. The maximum heart rate you are checking for in your class is the maximum training heart rate, recommended by most experts to be no higher than 90 percent of your maximum heart rate.
People beginning exercise have higher heart rates until they get trained. They also feel more breathless and should exercise at a lower percentage of their target heart rate until they are comfortable.
Exercising above 90 percent of your MHR moves your body from aerobic exercise (with oxygen) into anaerobic exercise (without oxygen).
Anaerobic exercise mainly depends on glycogen stored in the muscle for fuel instead of burning more efficient oxygen supplied by the bloodstream. Waste products build up quickly and the blood flow is inadequate to remove them. Hence the fatigue that quickly develops when you sprint or do your aerobics at a anaerobic level.
A few minutes rest allows the blood flow to remove the built-up wastes and you can continue your exercise. Anaerobic exercise, or "speed-work," can be an important part of any healthy woman's workout without fear of suffering a heart attack.
Taking your own pulse while exercising is a lot trickier than it sounds, and getting an accurate pulse rate under these circumstances is very difficult.
Why is it so difficult to take your heart rate?
Your pulse rate drops quickly when you stop exercising. It may take you time to find it, by which time the heart rate has decreased. It should be taken within ten seconds of stopping.
Often people make the mistake of starting the count when "zero" appears on their digital watches, and stopping when the "seven" appears. This may account for some of the high pulse rates in your class. You must stop counting as soon as the "six" appears.
After all, if you start at "zero," when the "one" appears, one second has elapsed. So when the "six" first appears your six seconds are up. Some classes take the pulse for 10 seconds, which increases the accuracy.
Other reasons your heart rate may be too high are dehydration, fatigue, infection with or without fever, anemia, obesity, or use of certain drugs, including diet pills, decongestants, caffeine, manjuana, or cocaine.
It is theoretically possible that exercising with a fever can cause some damage to the heart muscle, so never exercise aerobically when you are sick.
Everyone is an individual, and has different tolerance for exercise and endurance. Using your pulse rate as the sole determinant of your exercise level is best done in the early stages of your conditioning program to make sure that you are getting into the target training zone.
Once you are confident of your stamina and have learned how your body feels during and after workouts of specific times and distance, there is not much benefit in stopping your exercise to take your pulse.
Try to develop a more holistic appreciation of your exercise, taking into consideration if your legs feel wobbly, your lungs are burning, or if you feel dizzy or nauseous. These are also indications that you are overdoing it and need to slow down.
About the authors: Carol L. Otis, M.D., is Chief Medical Advisor to the Sanex WTA and a UCLA student health physician. Roger Goldingay is a former professional soccer player. They are married and the co-authors of The Athletic Woman's Survival Guide.
