Estimating your heart rate
If you use a heart-rate monitor to guide your training, you need to know what your maximum heart rate is. The longstanding conventional wisdom, proposed in the 1970s, was that subtracting your age from 220 would give a reasonable estimate of your max – so a 45-year-old, for example, would have an estimate max of 175. In 2001, researchers at the University of Colorado proposed a revised formula, in which you multiply your age by 0.7 and then subtract the resulting number from 220.
The problem with both these formulas, from a runner’s perspective, is that they were developed based on measurements of sedentary people. But there’s some evidence that regular training can lower your maximum heart rate, thanks either to changes in heart function or in other properties like the total volume of blood in your body. So do the formulas still work for runners? That’s what researchers in Greece decided to test, with a sample of 180 male and female recreational marathoners ranging in age from their 20s to their 70s.
The results, which were published in the journal Frontiers in Physiology, compared the maximal heart rate measured in a treadmill test to exhaustion to predictions of the formula – and the verdict was a mess. In women, both formulas overestimated the measured max by about five beats per minute on average (roughly 180 to 175), consistent with the idea that training lowers maximum heart rate. But in men, the formulas slightly underestimated the measured max, with the revised formula providing the most accurate estimate.
The most important takeaway, though, was the wide variation in individual heart rates. There were 40-year-olds in the study with a maximum in the low 160s, and other 40-year-olds with a maximum above 200 beats per minute. No formula that relies on age will ever be able to give a reliable individual estimate, because humans vary too much. So the best way to pin down your max is the wear a heart rate monitor in your next 5k race. Start relatively slowly, to ensure that you don’t fatigue prematurely, pick it up to normal race pace in the middle kilometres, then gun the last kilometre as hard as you can. The number on your watch when you cross the line is the one you should trust.