I am 46 years old, and a keen cyclist. I ride perhaps 3 times per week, training for a couple of sportives a year. I just did the Birmingham 100-mile, during which my average heart rate was 162 beats per minute (bpm). This suggests that I was working at 90%! My question is, is this good or bad for me, or is my heart rate monitor not working?
The accuracy and reliability of wearable heart rate monitors depends greatly upon the technology being employed. Chest strap monitors employ electrocardiography, detecting changes in electrical potential (voltage) in the heart. The accuracy of these devices, provided that they are fitted correctly, is typically in the order of 99% or greater. By contrast, the data from wrist-worn monitors, which detect blood volume changes in the periphery using optical sensors, may correlate with the ‘real’ values as little as ~0.5 (concordance correlation coefficient).
It is entirely possible that, if you have been using an optical/wrist-worn device, your data might include a considerable degree of uncertainty.
Nevertheless, the classic formula used to predict Maximum Heart Rate (H/Rmax) of H/Rmax = 220 – age, which was derived from research by Fox, Naughton, and Haskell in 1971, has been demonstrated to produce a Standard Error of Estimation (SEE) in the range of 7-12 beats per minute. According to Robert A. Robergs, PhD, the formula “was not developed from original research, but resulted from observation based on data from approximately 11 references consisting of published research or unpublished scientific compilations,” and that it therefore “has no scientific merit for use in exercise physiology and related fields.”
Alternative formulae have been proposed, notably H/Rmax = 208 – 0.7 × age that by Tanaka et al, which was the product of a meta-analysis of more than 350 studies. However, this too has a high SEE of around 10 beats per minute.
Research has consistently demonstrated Maximum Heart Rate to be subject to high individual variation. It is therefore likely that it cannot be predicted reliably with an age-based formula.
In order to predict your training zones accurately, therefore, it is necessary to test your maximum heart rate directly. And provided that you do not suffer from any medical condition—medical clearance is warranted—it is perfectly safe to do so.
I hope that helps.