After running fairly consistently for about 18 months now I recently got a Garmin thing that does heart rate monitoring, and I’ve just been reading about how to use it to train properly.

I appear to be doing something wrong and just wondered if there was a layman’s guide to how these things should work.

I’m late 30s, so theoretical max HR is about 180bpm. I did a 14km run the other day and my recorded average HR was 90% of max, very slowly creeping up towards 95% as the run went on. Except I was absolutely fine, not out of breath, chatting to the guy next to me. I only stopped running because I got bored. Everything I’ve read so far suggests this kind of exertion should leave me puffing and panting, and I should be aiming for this HR only during short intervals.

So questions are:
a) is my HRM completely and utterly gash (wrist based), and should I really be using the chest strap?
b) if not, am I likely to do myself a mischief running at these heart rates?

Some people have higher heart rate than others. Do a test to find your maximum then base your zones around that.

should I really be using the chest strap?

Probably

if not, am I likely to do myself a mischief running at these heart rates?

Probably not.

The real answer (this should really be a sticky given how often it comes up) is to do a LTHR test to determine your zones:
https://www.trainingpeaks.com/blog/joe-friel-s-quick-guide-to-setting-zones/

As above, the theoretical maximum heart rate zone is just an average of the population, and applies to no-one I know!

I’m almost 40, so my max should be 180, but I actually have a max of 208!

You need to do a test, like a lactate threshold heart rate (LTHR) test and set your zones based on that. Searcg for Joe Friel or Andy Coggan on Google.

Also note that, for running, your heart rate in a zone is likely to be higher than in the corresponding cycling zone. You ideally need to do two tests – one for cycling and one for running.

I find the garmin optical HRM works fine (fr235). Better than the chest strap ever was actually. But other than that, your “theoretical” max is probably wrong and anyway the rules about % max are only rough guides anyway. My pulse has never corresponded usefully to the general guidance but I have learnt over time what I’m capable of and it’s a useful guide for me. Especially if you repeat some rides/races you can quickly learn what is sustainable and what is not.

As an alternative to HR-based thresholds, about 2 min/mile slower than 5-10k race pace is probably a reasonable speed for just running around, add some faster efforts if you want.

Theoretical HR is bollocks.

Do a warm up

Then run for 30 mins, 10 mins building upto an effort you can hold for a further 20 mins, this will give you your lactate threshold hr

https://www.trainingpeaks.com/blog/joe-friel-s-quick-guide-to-setting-zones/

Enjoy……..

If your HR is at 90% and creeping up to 95% then your supposed MHR is too low. I’m 58 so my MMR according to the 220 – age formula should be 162 but I can sit at 175 for several minutes so I suspect, but have never verified, that my MHR is around 190

Do a running specific threshold test to get a better value for you for your LTHR. Your zones are specific to you and can change over time so you need to retest at regular intervals.

I’ve a Polar HRM and I found their chest strap to be fine when running. I also don’t have a problem with the Garmin chest strap when cycling.