Hmmmm, I never noticed anything like that in my own experience. I think I must be able to recover like mad though. I can ride and ride and ride and do it again tomorrow. I don't wear a monitor when I ride anymore. I think that my max heart rate has decreased a bit over the years. But that has been gradual.

Now I have never had any thing like over training. I seem to always know when to ride easy on a particular day.

Now you might just be getting more efficient. As your conditioning improves, it takes less heart rate to get the same speed. But even with that, you should still be able to hit the same max heart rate and still hold your heart rate at the same levels. So it could be over training. Of course, it could also be that you did not keep very good track of your rate earlier. If you do not keep a detailed log, it is easy to get fooled.

A less fit rider will send their heart rate to max much faster. Once you get into shape, it takes some doing to do that. You might not really be "needing" to do this on the courses you are running.

Hermes has good advice and could well be true. If you have a tendency to really push hard, you could well be over doing it.