Just another voice to dismiss the nonsensical max of 220 minus age. I started with a HRM back in 1993 and had a max of 183; last September I tested my max again and it was...183.

There is a lot of information about heart rates out there, the best being based on lots of individuals' experience. You must test, use4 trial and error, and/or have a coach help you find out your correct zones for racing. I know from experience that I can sustain 155 to 160 for one and a half to two hours steady pace, but can keep up 140-150 for four hours or more. Upper 160s and my legs start to burn. But those are for me, and only me. They only vary - increase in fact - if I have a lay off due to illness or injury and then I find that it is easier to achieve a higher rate for a given perceived effort when I start riding again.

The spanner in the works is that those are training levels, on my own. In a group, or especially in a race, my rate for the same perceived effort is hgher. If I even think of a race when training I can see my pulse rise for the same effort - the power of thought and imagination no less!

HTH