I’m catching up on old posts.
The example for heart rate zones will tend to set the target heart rates too low for most riders.
I find a better formula is:
(Max heart rate - resting heart rate) X zone percentage + resting heart rate.
For me, my observed max HR has been 164 bpm and my resting is 52. (this year)
164-52 = 112,
Zone 5 is 152-164 ( 112 X .90 = 100, 100 +52 = 152)
Zone 4 is 141 - 151 (112 X .8 = 89, 89 + 52 = 141)
Zone 3 is 130 - 140. (112 X .7 = 78, 78 + 52 = 130)
If I take a straight percentage of my max, 164 X .90 = 147 (zone 5 would be 147-164)
This make the zones too big and the lower zones are way too low.
The explanation is not as complicated as the formula looks.
When you take 90 %, 80%, 70% etc of your maximum heart rate you are also subtracting 90%, 80%, and 70% of your resting heart rate.
Your resting heart rate is fixed (relatively) and so is your maximum HR.
So you should take a certain percentage of your Vital heart rate.
The vital heart rate is the pulse from the lowest(resting HR ) to the highest HR. (Max - resting) and this is the pulses you can manipulate with exercise.
Now over time we can see changes in max and resting HR based on fitness and age.
Some changes good, others - not so much.