Thanks for your comments Brian and Matt. RPE worked well for me on a shorter race, but in a recent trail half marathon I needed breaks towards the end – in retrospect this was when my heart rate was going above LTHR. Made me wonder if I’d have had a more consistent run if I’d controlled effort earlier.

Brian – how do you set your goal HR for a race? This article may be of interest https://endurancebikeandrun.com/blog/2019/1/8/why-run-trail-races-with-a-heartrate-monitor