Have you used the same HR strap for the last 4 years? I had one that started reading above 200 a lot and I got suspicious when I started hitting 220 and 240s so I ended up getting a new HR and only once with the new HR did I get to 190, most rides 180 seem to be my max. I checked with my old monitor on the new strap and it worked fine again so it was just defective strap. I replaced it with a cheap ebay one and it worked fine with that. I don't know anything about overtraining so I can't comment on that, but if you haven't checked with another monitor that might be something to consider.