Join Date: Oct 2010
Location: New York State
Bikes: Thorn Nomad Mk2, 1996 Trek 520, Workcycles Transport, Brompton
My understanding is that max heart rate formulas are just rough guesses. To tune one's workouts accurately, one needs to measure one's max heart rate, really just by pushing oneself really hard. Similarly, it is best to know one's resting heart rate, which is best measured waking up in the morning, before any exertion, even standing up or best without even reaching for the HRM equipment - i.e., wear it overnight! With those two extremes, one can then set intermediate zones accurately.
So one cannot use an HRM and a formula to set a limit to one's level of exertion. One needs other criteria for that. Like especially please do not kill yourself!
I don't know that max heart rate changes much but for sure as you train you will be able to do the same workout at a lower heart rate or also more able to sustain a high heart rate for a longer time.