220 minus age is a formula widely adopted but discredited, for the average person's maximum HR, let alone active cyclists. Even the doctor who suggested in the 1980s it says it's very poor - it was derived from data from ill patients.my ‘Max’ heart rate should be 220-45= 175bpm which is utter drivel
The Tanaka formula gives a reasonable fit to the max HR line (graph of HR v age):
Tanaka formula(men and women over age 40): 208 - (0.7 × age)
But this is just a negative gradient line, with a wide variation between individuals.
For me this formula was up to 40 beats out 20+ years ago and is still 25+ beats 'out' (measured with Polar HRM bitd and with a Garmin last month, both with chest strap sensor). As I've said before, I acknowledge that I'm an outlier (and just share my data to illustrate the variation is not just statistical) and that others have properly measured maximum HRs below the figure derived from the formula. [Proviso: after an all-out effort, not by extrapolation of a ramp test.]
But it's harder maths so most sites just trot out the 220-age cobblers.