I remember setting those on my Garmin and then AP coming up with some other set of default levels. Maybe your AP levels aren't what you think they are?
Good suggestion. I'm actually not using the Garmin's heart rate levels, just the raw data. The ranges I quoted are from my Attackpoint settings.
I think I'm just out of shape.
Or the battery is dying and not picking up as well as it used to... you can always do a manual check against your pulse.