Spike, have you seen that Tanaka formula I posted above?
I'm familar with it - I actually like it when I do cardio for myself JUST to burn fat - I used it for my last show - its kinda 'new' in the execise sci comm as far as use but it good for athletes and more conditioned ind or people already aerobically inclined by training - its more accurate than 220-age
I also like the karvonen formula using your method combined: resting HR should be taken into account I believe
Below is an example of the Karvonen formula for a 23 year old person with a resting heart rate of 65 beats per minute
206.9 - (0.67 x 23 (age)) = 191
191 - 65 (resting heart rate) = 126
126 * 65% (low end of heart rate zone) OR 85% (high end) = 82 OR 107
82 + 65 (resting heart rate) = 147
107 + 65 (rhr) = 172
The target heart rate zone for this person would be 147 to 172