Originally Posted by genejockey

Perhaps it means you could push harder if you wanted to?

Also, as I understand it, HRmax is not a function of most of the factors you suggest. It is not something one can change with training, either. I do know that the HR I reach while putting out a particular power or speed is subject to all of those.

The first time I hit my HRmax, about 20 years ago,I was riding in a fast group ride going about 30, and felt so good that I pulled out of the group and sprinted ahead of them, uphill, into the wind. I just blew past them, pushing as hard as I could and suddenly it was like I hit a wall and my legs turned to jelly, and I couldn't do it anymore. 193 bpm at about 43 years old. I hit 191 5 years later - felt exactly the same. So, not only far off of 220 - age, but also the linear 1bpm/year doesn't work, either.