A couple of blog comments sparked the following question from Chris:

As I rode the Zoo my heart-rate hovered between 180 and 184. 184 is the absolute highest I have ever seen for me on a bike. My resting heart rate is roughly 56. Out of curiosity.... can anyone explain what it means that I have a higher resting heart rate and apparently a higher max heartrate than Eric.

That's simple. I have achieved the morally superior lower heartrate, and it doesn't matter how much faster you are, I'm going to be the better cyclist.

Don't buy that? Well, it's a simply matter of physiology. We aren't surprised that certain people have larger hands, or heads, or ears than others, so it's probably not a surprise that people have different sized hearts. My heart is simply bigger than yours. In fact, the stroke volume (the amount of blood pumped per beat) can vary as much as 4x between people. That's an impressive difference, though it would admittedly be more impressive if I hadn't pulled that "4x" number out of thin air.

I used to work out with a woman whose heart rate at comparable level of exertion would be be something 1.6 times my heart rate. I'd be hanging out at around 120, she'd be up above 190. No problem for her, but a great indication that things like "heart rate ranges" and "220 minus your age" don't work well with the whole population, and may be pretty bad for specific individuals.

As you may already know, increase in stroke volume is one of the primary adaptations from training.