So here it is.
Fastest 10km you can do, but keeping your HR under the 75% range as defined by the Karvonen formula
The idea is to keep the HR steady after the initial rise.
Peeking over the ceiling for short periods is allowed, but the aim to keep just under the max level.
Funkster - RHR 39 / MHR estimated 170
Average 126bpm / Max 135bpm