Lately, even when I'm riding hard, I'm not getting into my maximum HR range very much. I'm not sure whether I need to make the hard intervals harder and/or longer; or whether I'm not working as hard as I think I am; or need to re-adjust my HR zones due to increased fitness; or may even be approaching overtraining. I hope it isn't that last!
But I must say, a power meter would come in handy right now. If I saw that I were pedaling at a certain level of force, even though my HR weren't at max, I'd know I had become more fit. If the power meter showed low force when my HR were at max, I'd know I needed to take it easy that day.
Incidentally, some say that calculating your maximum HR by the formula of "220 minus your age" isn't the most accurate method. In my own case it's close, but that doesn't guarantee that this formula will work for the next person.
Sometimes trying to train by HR is frustrating, as this morning was. After two days of riding pretty hard, I had planned an easy, short, zone 1 ride for today. With a wind that was blowing at least 20 mph, I was in zone 2 about a third of the time.
I hope Tour de Cure isn't plagued by strong winds again this year. That would be -- well -- disheartening.