Heart rate will definately fall as you get fitter. As far as i am concerned when i begin a new plan (usually following a broken bone or an operation) i use perceived exertion alone until i get to a half decent level of fitness. I start using training zones etc when the zones were useable tools and that little alarm stopped going off constantly. To give you an idea i started training at christmas following four years of relative inactivity. I was extremely overweight and had a rest heart rate of 88. Its now 46! Prior to my 4 year lay off i was training hard for rugby etc so my heart has reviously been strong but its still one hell of an improvement on the recent sedentasry me. Guess ill never have the heart of 'big mig' but its all going in the right direction. ( Weight and heart rate down speed and performance up)