HRM Reliability?

The most common causes of poor OHR readings is poor positioning and placement. Excessive movement of the watch on the wrist allows light to enter the sensor, interfering with the measurement of light changes due to blood flow changes with each heart beat. The watch band should be snug, and positioned on the fleshy part of the wrist, well away from the wrist bone. I find I have to tighten the strap an extra notch on my runs, than I do to get accurate measurements during the rest of the day. The more vigorous arm movements of sprinting (versus your regular running pace) may be causing problems here.

But something that affects pretty much all OHR's is the lack of responsiveness - compared with chest straps, they are much slower to detect changes in HR with intervals. When you add in the fact that HR itself is a lagging indicator of effort, this can mean that the peaks and troughs in your HR can show up well after you have begun or finished each interval (especially shorter intervals).

I suspect that your issues may be due to a combination of both of these effects. Out of curiousity, what is the OHR reading during the recovery periods?

If you are going flat out during the intervals and just using HR for POST-event analysis, you may be able to live with just tightening the watch strap, knowing that the timing will be off but the averages OK. If you are using HR to gauge your DURING intervals, then you may be better off using a chest strap for interval training - the F5 is compatible with both ANT+ and BLE straps.

Here's a graph comparing how the OHRM and chest strap HRM tracks during interval training. The orange line being the chest strap data and the grey being the OHR data. As you can see the OHR completely misses sudden increases in HR most of the time. I believe this is as a result of filtering that is in place to try eliminate false readings. My recomendation is to use a chest strap HRM for interval training.ciq.forums.garmin.com/.../1243831.jpg

Many thanks for your replies.

The watch band should be snug, and positioned on the fleshy part of the wrist, well away from the wrist bone. I find I have to tighten the strap an extra notch on my runs, than I do to get accurate measurements during the rest of the day. The more vigorous arm movements of sprinting (versus your regular running pace) may be causing problems here.

I've been conscious of this, and have tightened the strap as snug as it will go.

But something that affects pretty much all OHR's is the lack of responsiveness - compared with chest straps, they are much slower to detect changes in HR with intervals. When you add in the fact that HR itself is a lagging indicator of effort, this can mean that the peaks and troughs in your HR can show up well after you have begun or finished each interval (especially shorter intervals).

I suspect that your issues may be due to a combination of both of these effects. Out of curiousity, what is the OHR reading during the recovery periods?

I did consider this possibility, but the OHR reading almost immediately starts to go down during recovery periods. E.g. on my fourth rep, the reading peaked at 145 bpm at the end of the rep (i.e. the top of the hill), but dropped to around 125 bpm on the jog back down the hill. Therefore I've never witnessed this lag. A similar thing happens with any short bursts of hard effort.

I only ever get the reading up credibly high (I've maxed out at 191 bpm) with a gradual but sustained increase in effort - e.g. gradually increasing pace from say 7.40 mpm (with OHR reading of around 155 bpm) to 6.40 mpm, sustained for four or five minutes (with OHR reading of around 185 bpm) - which for for me is super fast!

Here's a graph comparing how the OHRM and chest strap HRM tracks during interval training. The orange line being the chest strap data and the grey being the OHR data. As you can see the OHR completely misses sudden increases in HR most of the time. I believe this is as a result of filtering that is in place to try eliminate false readings. My recomendation is to use a chest strap HRM for interval training.

This sounds plausible ? though not what you would expect from a ?600 watch ?

I think I will investigate a chest strap. I had one with my old Forerunner 210 (which I presume won't be compatible?), but found it inconvenient and uncomfortable - one of the reasons I went for the Fenix 5 with OHR!

Thanks again.
Dave

I think I will investigate a chest strap. I had one with my old Forerunner 210 (which I presume won't be compatible?), but found it inconvenient and uncomfortable - one of the reasons I went for the Fenix 5 with OHR!

It'll work fine - the current models are backwards compatible with every HRM that Garmin have produced EXCEPT the very first ones which came with the brick-sized Forerunner 301.
Newer ones have got progressively more comfortable, and also started to provide running dynamics, which the 210 strap didn't support. For heart rate,VO2max, R-R intervals and so on, no problem.

OHR is an evolving technology, especially on the wrist; a Scosche Rhythm+ will give you really good heart rate measurements, but the R-R values won't be the same as you'll get from a chest strap. And that device works better because you wear it further up the arm on an elastic strap, so the reading of the blood flow has higher signal and less noise from shaking around with your arm motion.

That is a good article.

Personally I find the straps chafe me across the breastbone, directly below the HRM unit itself; I put wide micropore tape across there before longer runs (anything over an hour or so). Protects the skin and doesn't interfere with the electrical contact.
Other people have used Polar straps instead of the Garmin strap (with the Garmin module attached). Didn't make any difference to me, YMMV.

Quick update: I dug out my old chest strap and, as you said, it paired fine with my 5S. What's more, it does, as suggested, give far more reliable HR readings on these hill sprints - with each rep it quickly accelerates into the 170s, maxing out at 179 on the final rep (and dropping to between 106 and 109 by the end of each 60 second rest period). And the chest strap hasn't been too uncomfortable either.

I have noticed though that every training session I have done with the chest strap returns a training status of 'Unproductive' - this is whether it's a long easy run, a short fast run, or a medium run with sprints and intervals. Not sure what I need to change to start making my training sessions productive - but I guess that's a topic for a separate thread ...

Thanks again guys for all your help.

Cheers,
Dave

Might be worth checking that your HR zones are correct?

I have a similar poor HRM reading problem. When I'm running the HRM works fine. But when I do some circuit training, the heart rate barely raises above my average resting heart rate. If I throw in some skipping or star jumps to the ciruit then the monitor jumps up to where I'd expect it to be, the minute I'm doing weights again, down it goes. Seems a bit poor for such an expensive device and totally screws up all my workout / progress stats.

Mcbadger, could you please advise if it's possible to pair Scosche Rhythm+ with fenix 5?