As you become more aerobically fit, you will make more power at a lower heart rate due to increased cardiac stroke volume and if you keep at it long enough, better economy due to metabolic changes in the" muscles".
I did 126 miles in 6:30 moving and just under 7 hours total the other day and my average HR was a littler higher than usual, some due to lack of fitness and some because I overheated and decoupled badly. I did 205 watts and 128 BPM.
Today, I did an easier zone 2 ride for 2 hours and 30 miles with 1500 feet of climbing. 171 watts and 106 BPM HR.
My Max HR is 172 on the bike and 183 running. I can ride at about 153 bpm for approximately an hour but very, very rarely ride that hard. Most of my riding is under 120 bpm. I'm not quite 64 yet. I really do not use max HR at all although it is interesting theoretically to assess how close to one's potential one can get but that is too complex to write here. It has to due with fractional utilization of VO2 max at lactate threshold.
HR and aerobic power should be linearly related in the steady state aerobic power levels and should not change meaning the HR should not creep up and up over the course of the ride at the same power or effort level. That could mean dehydration, it could mean you are getting very cold, or more likely it means it is time to end the training ride soon. This is one way I use a HRM.
Last edited by GhostRider62; 05-03-22 at 07:59 PM.