Calculating the Heart Rate Reserve

Runner Checking Heart Rate Monitor
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The heart rate reserve (HRR) is the difference between a person's resting heart rate and maximum heart rate. It is the range of heart rate values that you can see for an individual, between the lowest they have at rest and the highest they can achieve through exertion. 

Heart rate reserve is used to calculate heart rate exercise zones by the Karvonen formula. In studies, the heart rate reserve has been found to compare well with the oxygen consumption reserve (VO2R) for estimating exercise energy expended at different exertion levels.

Target Exercise Intensity

The Karvonen Formula uses the heart rate reserve number before calculating heart rate percentage of maximum numbers for target heart rates. You need to know your resting heart rate by taking your pulse first thing after awakening and before you get out of bed.

Then you need to know your maximum heart rate, which can be estimated by subtracting your age from 220 (classic Karvonen Formula) or 206.9 - (0.67 x age) with the updated formula.

This formula may not be accurate if you are in very good aerobic condition for your age. So, athletes may use other methods to determine their maximum heart rate.

With these two numbers, the Karvonen Formula is Exercise HR = % of target intensity (HR Max – HR Rest) + HR Rest. The middle term is the heart rate reserve, which is then multiplied by the percentage of target intensity desired, and then the resting heart rate is added back in.

If you want to exercise in the moderate-intensity zone, the percent of the target intensity defined by the CDC is from 50% to 70%.

Increasing Your Heart Rate Reserve

Maximum heart rate is mostly age-based and difficult to change with exercise, with only small effects seen. The implications for heart rate reserve is that you would increase it most by lowering the resting heart rate. The resting heart rate is seen to be lowered by increasing cardiovascular fitness, although overtraining can result in a temporary increase in the resting heart rate.

To achieve a larger functional heart rate reserve, the chief mechanism is to lower the resting heart by building cardiovascular fitness with activities such as brisk walking, jogging, running, cycling, and other endurance exercises.

These cardio exercises challenge the lungs and heart and when engaged in regularly they build cardiovascular capacity.

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