How to calculate your target heart rate (THR)

Next you need to calculate the lower and upper limits of the THR. Zone Three intensity exercise starts at 70% of maximum heart rate.

Upper limit: Zone Three intensity exercise reaches its peak at 85% of maximum heart rate

So the THR for our 40-year-old individual will be between 126 and 153 beats per minute for Zone Three exercise.

It’s common to find that the heart rate of a person decreases – both when they’re not exercising and during exercise at all intensities as they get fitter. The normal resting heart rate is around 72 beats per minute – with training this can often decrease to 55 beats per minute, or even lower. It’s worth reflecting that this 17 beat per minute decrease is equal to a total reduction in heart rate of 8,935,200 beats a year!

To understand how the heart adapts to training, it’s important to appreciate that the heart is a pump, designed to send blood around our bloodstream. Even after we get fitter, the body's demand for blood at low exercise intensity doesn't change. However, the heart is able to pump more blood if we need to work harder. It achieves this through strengthening the muscles that form the walls of the heart, and by enlarging the chambers of the heart that briefly store blood between each heart beat. These adaptations make the heart a more efficient pump, able to expel more blood with each beat. Since the body still needs the same amount of blood, the heart can afford to slow down and still supply the blood and oxygen that we need.

A simple summary of the four heart rate training zones is given in this table – you may find it helpful to print this out as a handy reference guide for use when training:

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Heart Rate Training Zone

How often should I train in each zone?

The answer to this question depends on your objectives and how fit you are. The key zones for the majority of people are Zones Two and Three, the ‘Health’ and ‘Aerobic’ Zones. These are the ones in which the majority of your exercise should take place. Using the example of someone exercising five times a week, two of these sessions should each be undertaken in Zones Two and Three, with one in Zone One. Fitter individuals may wish to eliminate the Zone One session, and replace it with an additional Zone Two or Zone Three session. The very fit should attempt an occasional Zone Four work out.

By sticking to a ‘scientific’ method of controlling your training intensity through the use of heart rate monitoring, you should avoid both over- and under-training. Start each session at the lower end of the THR zone, because you’ll find your heart rate will gradually creep up as the session continues. In this way, you will get a progressive and sensible improvement in health and fitness, and also gain more enjoyment and satisfaction from the exercise sessions that you’re doing.