I am getting back into cycling, now that I'm 50, after having done a lot of riding 20 years ago. (I know, what the heck was I thinking, stopping for 20 years!) Anyway, I find that my goals are totally different than before. Miles arn't as important to me, it is about duration, or time. Speed isn't important, endurance over time is what counts for me now.
I have worked my way up riding 2 hours contiuously, fairly comfortably, every other day. Speed isn't great, average has been about 14 mph. But I have been feeling a much better than I have in a long time. (I find myself craving that supercharged feeling you get a couple days after riding a century.)
Anyway, the yesterday I got a heart monitor (I alway rode with one 20 years ago) and found that when I rode today, I had to keep backing off the power, downshifting and taking it easier than I thought I needed to. My goal was to maintain an average heart rate fo 135 bpm for two hours. It really made the ride enjoyable, rather than pushing myself I found that I was enjoying the scenery. I also found that I tended to use a slightly higher cadence. It just felt easier and more efficient. Well, apparently it was because after riding for 2 hours I covered 30 miles, with an average of 15 mph. Now, I know I just got done saying that speed isn't my goal, but this illustrates to me how riding with a heart rate montor can be beneficial in more ways than I thought. I am looking forward to the scenery on my next two hour ride.