Ever had your heart rate skyrocket early in a race and wondered whether to slow down? I faced exactly that at the Valencia 15K — and it taught me when to ignore heart rate and trust perceived effort instead.

Last week I ran the 15k Nocturna Valencia. Whenever I race, I have a plan. For this race it was easy: first 2k, easy-ish until 8k, unpleasant for the rest, full gas 3k from the end. That approach gives me a good shot at a negative split and makes the race much more enjoyable.

Planning the race

That’s not always easy to know but I can use heart rate as a proxy. My previous race data shows me that my LTHR always sits around 162-166bpm. Below that threshold I can run for over an hour, maybe several. Above that and my time to exhaustion is much less than an hour. This is helpful for pacing a race. I also know that it takes about 2k for my HR to stabilise.

Putting this into practise means that I can expect the first half of the race to be below threshold (150-160-ish) and the second half to be at or slightly above threshold. Pretty simple.

P.S. I never race to pace. There are far too variables that can affect my ability to run a kilometre in a given time.

What actually happened

The first kilometre passed and my Garmin indicated that I had completed it in 4m07s. I thought that was ok, it would have been nice to have gone faster but 4:07 is ok. Then I saw that my HR was already at 160. Shit! Had I started too fast?

Slow down or push on?

HR can be affected by a bunch of things. It was a warm evening, 23º and I hadn’t done any heat adapted training. I did a proper taper. My HR tends to be slightly depressed when in the middle of a block of training.

Given the heat and taper, I decided not to overreact. If I’d slowed down just to hit my usual HR zones, I’d have risked underperforming.

HR stayed flat until midway; after that I ran based on RPE.

Trust heart rate, but verify with feel

Heart rate can be a brilliant pacing tool, but it’s not gospel. On some days it’ll be off — heat, fatigue, taper, nerves — whatever the reason. That’s when RPE becomes your best ally.