The most prominent and accurate means of determining target heart-rate is the Karvonen formula. This formula calculates a percentage of the heart-rate reserve, which is the difference between the resting heart-rate and the maximal heart-rate.
Heart-rate reserve = maximal heart-rate – resting heart-rate
Maximal Heart-rate is the highest rate a person can attain during exercise. While an electrocardiogram test would provide the most accurate MHR, for practical application an age-predicted heart-rate formula was developed.
Maximal heart-rate = 220 – age
This formula is based on the assumption that one’s heart rate at birth is 220 and decreases by one every year. The accuracy of determining maximal heart-rate based on this formula can vary at any given age by + 10 beats per minute.
Resting Heart-rate is the rate at which your heart beats at full rest. It is recommended that this rate be taken before getting out of bed, counting the pulse for a full 60 seconds, 3 mornings in a row and averaging the counts.
Determining the target heart-rate ranges
Using the Karvonen formula, the generally accepted heart-rate ranges are between 60% to 80% of maximal heart-rate reserve.
Target heart-rate = % intensity X heart-rate reserve + resting heart-rate
Here’s how it would be calculated for a 45 year old with a resting heart-rate of 80 and an age-predicted maximal heart-rate of 175 at an 80% intensity level of maximum heart-rate reserve:
175 (age predicted MHR) – 80 (resting heart-rate) 95 (heart rate reserve) X.80 (intensity level) 76.00 +80.00 (resting heart-rate) 156.00 (target heart rate)
It is recommended that the formula be applied to both ends of the range, 60% and 80%, to determine the target heart-rate training zone.
The Karvonen formula is considered more accurate than the Maximal heart-rate formula, because the resting heart-rate is used in the calculation. From a practical standpoint, few people actually figure out an average for their true resting heart-rate.
Maximal Heart-Rate Formula
Therefore the simplified Maximal heart-rate formula is the standard that was used in most group exercise settings:
target heart-rate = maximal heart-rate (mhr) X % intensity
For the same 45 year old, here’s how the range would be figured:
At 60 % Intensity -
175 (mhr: 220 – age) X.60 (percent intensity) 105 (target Heart-rate)
At 80% Intensity -
175 (mhr: 220 – age) X.80 (percent intensity) 140 (target heart-rate)
In group fitness settings, easy reference for intensity levels may be provided with a Target Heart Rate Chart.