The Karvonen formula is junk because it uses the 220-AGE formula as your max heart rate. That part of the formula is totally bogus. If your max HR happens to equal 220-AGE it is purely coincidental. If you know your REAL max hr, this formula may have some merit. I dunno. However, given what I already know about the Karvonen formula (220-age myth), I really find it difficult to take it seriously.
The first thing you must do is to determine your max HR. (hint: don't use a formula based on age) Then, you can work on ranges. Without a GOOD max HR number, all information derived from this number (your hr ranges for one) are bogus.
... Brad
I don't think your statement is correct. I have tested my max HR at 202. I am 47 so agree 202-47 is junk. 155 is my regular ride HR, not the max. The formula uses known max heart rate and known resting pulse to calculate the heart rate reserve.