There are generally two ways to use heart rate to determine intensity. The first is to simply take a percent- age of your athlete's maximum heart rate (max HR). The approximate max HR can be determined by subtracting an athlete's age from 220. For example, a 20-year-old's max HR would be approximately 200 beats per minute (220-20), and a target range of 70 to 80% would correspond to 140 to 160 beats per minute.
The second method of using heart rate to calculate a target range involves the athlete's resting heart rate. This method is called the Karvonen method, named after its founder. To calculate an athlete's target heart rate, subtract resting HR from max HR before multiplying by the desired percentage. The resting HR is then added back to the product. The difference between the max HR and the resting HR is called the heart rate reserve (HRR).
If the 20-year-old in the above example has a resting HR of 50 beats per minute, a target heart rate of 70- 80% HRR would be calculated as follows:
HRR = (220-20) - 50 = 150 beats/ min. Lower Limit = (150 x 0.70) + 50 = 155 beats/min. Upper Limit = (150 x 0.80) + 50 = 170 beats/min. The Karvonen formula is especially attractive to use since it also estimates the running intensity in relation to the athlete's maximum oxygen consumption (VO2 max). For example, 75% HRR equals 75% VO2 max. (There is about a 10% difference when comparing either %HRR or % VOmax to %max HR, however. For example, 75% HRR equals about 85% max HR.)
When using the Karvonen method, you should retest your athlete's resting HR once every few months to recalculate a target range since resting HR decreases as cardio- vascular fitness improves. However, there is a limit as to how much the resting (or running) heart rate will decrease in response to training.
Remind your athletes that the goal is not a heart rate of zero. The lower resting heart rate in endurance- trained runners results from a combination of an increased stroke volume (the volume of blood pumped by the heart's left ventricle with each beat) and an increased activity from the parasympathetic nervous system. Since max HR decreases with age (by about one beat/min. per year), you should also readjust the target HR as your athletes get older.
It is important to remember that the formula "220-age" provides only an estimate of the max and may be off by more than 10-15 beats/min. All people of the same age do not have the same max HR (Wilmore & Costill, 1988). In fact, 68% of the population will have a max HR within one standard deviation of the population's average, with 95% falling within two standard deviations of the average.
This rather large margin of error can lead to prescribing a running intensity that is either too low or too high to achieve the optimal benefit. The equation tends to overestimate max HR in highly trained runners and underestimate max HR in un- trained people. A more accurate way to determine max HR would be to measure your athlete's HR while he performs an all-out test, such as a race or a time trial.
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