This method of calculating your target training zone is based on your maximal heartrate and resting pulse.
The correlation here is more directly
linear: 60% to 80% of your Heart Rate Reserve, HRR, equals 60% to 80% of
your functional capacity.
To determine your target training zone with HRR, do this:
Take your resting pulse three mornings in a row, just after waking up. Add
all of them together, and divide by 3, to get the average.
Let's say your average is 60 beats per minute.
(220) - (your age) = MaxHR
(MaxHR) - (resting heart rate) = HRR
(HRR) x (60% to 80%) = training range %
(training range %) + (resting heart rate) = (your target training zone)
220 - 35 = 185 (MaxHR)
185 - 60 = 125 (HRR)
125 x .6 = 75 (60% training percentage)
125 x .8 = 100 (80% training percentage)
75 + 60 = 135 (target training zone, in beats per minute)
100 + 60 = 160 (target training zone, in beats per minute)
So, your target training zone, in beats per minute is 135 to 160. Of course,
to get a 15 second target simply divide each number by 4. That would be
34 to 40 beats over 15 seconds. When counting beats, start with the first
beat as zero: ie. 0-1-2-3-4...38-39-40.