BTW, I have never run more than 10km or 1 hour in my life.
I simply calculate pace and HR from what is suggested table 4 in academic article '
Crossing the Golden Training Divide: The Science and Practice of Training World-Class 800- and 1500-m Runners'.
which notes easy runs 60-72% of HR, marathon pace runs 73-82% of HR, half marathon pace 83-87% HR, 10km pace 88-92% of HR, 3-5km pace 93% of HR or above.
Sure it is not a perfect system given individual range differences, but I am finding it a good way to judge my run pace and lift pace as i get fitter.
A lot of my weekly mileage is in the 60-72% zone, but the three harder days are apparently most important for developing my aerobic power in addition to slower runs.