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HRM Tri - Frequency and Accuracy of readings on Garmin Connect

Investigation into the potential causes of a fall from my bike...

Hi - I couldn't find a specific HRM subforum so I'm using the one for the FR935 which I use it with.

I'm, interested in the second to second accuracy of the readings logged from the HRM, in this case, relating to a bike ride. I find that the HRM provides what I consider to be quite accurate tracks of my heart rate during bike rides - for example, when my speed drops whilst waiting at traffic lights I can see the Heart Rate dropping accordingly and often reassuringly quickly.

Last week I had a fall from my bike - no traffic, no other riders, just me and, I thought, a clumsy acceleration after a brief rest to refill my water bottle. I have no recollection of the fall as I hit my head very hard and knocked myself out. Various studies at the hospital and GP afterwards indicate that I might have had a blackout due to a heart block although I remain sceptical.

The heart would need to stopped for a few seconds to cause a blackout so I wondered if such a drop in heart rate would register on the readings sent from the HRM Tri. Would a zero reading for a few seconds show as zero (or very low) or is the tracked reading averaged for rates taken from the the previous 10, 20 or 60 seconds or something?

I can see no noticeable drop in Heart Rate in the Garmin Connect logs immediately before the fall - only after. From the clip below you can see the restart of the ride, an acceleration to nearly 28kms which is quicker than I though I was going, and then a quick drop in speed (obviously), subsequent lowering in HR and a spike in cadence presumably as my pedals spun while I fell (pretty sure I went over the bars with my feet still slipped in).

But there's no noticeable blip on the heart rate - should I expect to see one if my heart actually stopped or missed a few beats?
ciq.forums.garmin.com/.../1272651.jpg

0 Ollypsilon over 7 years ago

...
The heart would need to stopped for a few seconds to cause a blackout ...

Well, was this assumption confirmed by a doctor? My understanding of a blackout is something else than a cardiac arrest.

...
I can see no noticeable drop in Heart Rate in the Garmin Connect logs immediately before the fall - only after. From the clip below you can see the restart of the ride, an acceleration to nearly 28kms which is quicker than I though I was going, and then a quick drop in speed (obviously), subsequent lowering in HR and a spike in cadence presumably as my pedals spun while I fell (pretty sure I went over the bars with my feet still slipped in).
But there's no noticeable blip on the heart rate - should I expect to see one if my heart actually stopped or missed a few beats?

I think the graphs are smoothed. Maybe have a look at your original file and check with other tools to see all HR data recorded. If you don't have any tools you can send me your file and I'll extract HR data...

0 timgrose over 7 years ago

Sorry for you incident. That's obviously concerning.

I think it is difficult for any of us as purely users of the watch to accurately comment on such things. My observations is that the HR data from straps like the HRM-Tri has some sort of smoothing or at least a filter to prevent "spikes". In any case I would have thought you would really need the HRV "beat to beat" data to see if you can infer anything.

That said, from time to time, people have reported drop outs of HR for short periods which 99% of the time is likely to be signal drop outs rather than anything amiss with the user. The fact you do see zero HR in such cases suggests you might be able to detect a physical incident. Of course these HR straps aren't medical grade instruments.

I am not sure I can infer much from your graph. HR seems reasonably correlated with speed to me.

0 Dr Phil over 7 years ago

If you have concerns about the condition of your heart then you need to seek expert advice from the appropriate professionals. Even if you see a dropout on your HR trace, that is not necessarily indicative of a physiological problem. Dropouts can and do occur for any number of reasons.

0 Gregjohnmason over 7 years ago

Thanks folks - yes I have spent many hours in the presence of GPs and cardiologists during the past ten days and the diagnosis is still sitting in the "blackout" or seizure area (seizure potentially due to lack of heart pumped to the brain). I know that the straps aren't medical instruments and I did spend a day wearing a holter device for true beat-to-beat measurement which did show some dropouts (a dozen or so during sleep times - actually intermittent second degree heart block, although this on its own wouldn't normally result in a blackout but combined with no breakfast and maybe some dehydration maybe...). I also have an appointment with a neurologist.

I also tried a less than scientific experiment to test the logging but that proved inconclusive also (https://forums.garmin.com/forum/into-sports/garmin-connect/the-water-cooler/1272664-hrm-tri-frequency-and-accuracy-of-readings-on-garmin-connect).

I know I shouldn't be trying further self diagnosis but it's hard not to. I guess I'm just clutching at straws that the Garmin strap might provide some small additional piece of the puzzle. It probably won't but thanks for your concerns and replies.

In the meantime I'm restricted to "brisk walks" and volunteering at Parkrun, which although can be fulfilling, is also quite frustrating.

0 Dr Phil over 7 years ago

Good that you are seeking advice. Holter monitors are useful diagnostic tools but again, do experience dropouts. Sometime stuff happens. Friend of mine recently collapsed during a parkrun. No diagnosed heart condition but it obviously shook him as it was unexpected. As you have noted, it might just have been a 'perfect storm' - low blood sugar, low fluids, sudden exertion. My friend has gradually regained confidence to run faster. But he also makes sure he's not doing anything in a weakened state again.

Good luck.

0 Gregjohnmason over 7 years ago

Thank you - I suspect it'll be a long road before I know the true root cause. I just hope they can rule out enough that I can get back on my bike soon :-(