Heart rate reserve describes the difference between a measured heart rate or the predicted maximum heart rate and the resting heart rate in a person. It indicates the heart rate reserve cardiovascular fitness of a person.
How to calculate heart rate reserve
The formula used to calculate the heart rate reserve is HRR = HRmax − HRrest.
As the heart rate reserve increases the HRrest has to drop. This is a beneficial parameter that is calculated by athletes to increase their performance.
Heart rate and oxygen consumption
Heart rate has a relation with oxygen consumption especially when intensities rise to reach ranges between 50-90% VO2 max. Thus exercise intensity is the percentage of maximum heart rate (calculated using the formula 220 - age).
A 30 year old who has a maximum heart rate of 190bpm thus may train up to 75% of his intensity at 143bpm.
The earlier formula “220 – age” makes no allowances for variations in resting heart rate among individuals.
The formula for heart rate reserve allows a better target heart rate to be determined for optimum training capacity based on both maximum and resting heart rate.
Calculating Target Heart Rate with Karvonen Formula
220 - age = maximum heart rate
Maximum heart rate - resting heart rate = heart rate reserve
(Heart rate reserve X training%) + resting heart rate
Comparing the two formulas
To compare the two formulas, an example of a 45 year old man who has a resting heart rate of 60 beats per minute and who wants to train at 70% maximum is assessed.
Target heart rate in this individual:-
220 – 45 = 175 beats per minute. This is the maximum heart rate.
According to Karvonen formula (115 x 0.7) + 60 = 140.5
Thus 140.5 beats per minute is the target heart rate using this method.
Using the traditional 220 age formula this same person would have a target heart rate of (220-45 X 0.7) or 122.5
122.5 beats per minute is considerably lower than that estimated by the Karvonen formula.