Drop in Heart Rate afte riding on Bike Trainer for a period of time

The following is a description of an event that occurs with some regularity. I will be riding on my bike trainer for, say 30 minutes, with a heart rate of ~130-140 bpm. Suddenly, the rate will drop to 70-80 bpm, and stay there. Nothing I do will make the rate increase. Fortunately, it does not affect my ability to continue riding, with no apparent loss in power. Maybe 10-15 minutes laterm my rate will go back up to the original levels.

Does anybody have an idea why it does this, and how to reduce tthe occurance of rate drop?


Steve Triathlon

by stevebne - 2023-04-06 22:42:53


This is a well known problem and is due to baseline reset. The timing of this event once you start exercising is determined by the settings on your PM and the brand / model as each has a different algorhythm. Interestingly, it occurs in all sports, both outdoors and indoors. The solutions include changing the settings to a later baseline reset (BS usually calls this 'fitness level' for the minute volume sensor) or stopping for a few minutes (to allow your HR to move back to a resting rate) and restarting the exercise. As you have found, breathing harder or increasing your power doesn't work until a fixed amount of time has passed. 

If you look back at my previous comments in other threads, I talk about this in more detail.

I don't agree...

by crustyg - 2023-04-07 04:59:41

..and here's why.  If you're working moderately hard on the turbo/static bike and your HR really drops 60BPM it would have a major impact on cardiac output => much less blood to your big exercising muscles and you would *really* notice it.

Also, (pax, Steve), I don't accept a sudden baseline shift of your Accolade whilst maintaining a HR of 130-140BPM.  That's not how the device works.  *IF* your PM had detected a tachy even then it might drop the paced rate, but that would be very noticeable (see above).  There *is* a real issue with BostonSci MV if you keep letting your HR drop below 90BPM as this allows the long-term MV baseline to start to creep up so the delta (short-term minus long-term) becomes small and the feed into RR diminishes.

There is one other possible PM issue and I've had this happen to me more than a few times: for some as-yet unproven reason the PM drops the RR feed completely.  BostonSci say 'it's interference' but that's unlikely out in the countryside with no power lines, radio masts etc.

My guess: whatever you're using to measure your HR is losing track of your real HR.  I've tried wrist pulseox for swimming (Garmin Swim2) - useless.  Chest straps: OK as long as you moisten the underside (no problem once exercising hard due to sweat), but over time I've found that the elastic weakens and the strap can slide down - and as it's measuring Lead I which is a small signal to start with it can easily lose some beats => sudden drop in reported HR.  It's also possible that you're having short runs of an atrial tachy and most HR monitors will produce a sudden drop in reported HR during this time.  It used to happen to me a lot when running (during my long diagnostic journey to a re-entrant pathway => AFlut).  But in my experience this will also produce a very obvious impact on power/performance.

My best guess: your measuring tool gives the wrong answer at this time.  How to check: easy, feel your carotid pulse and just count for 10-15seconds.

Sudden massive drop in heart rate but completely symptom free? Amazing

by Gemita - 2023-04-07 07:10:04

RMarkley, your comment “Fortunately, it does not affect my ability to continue riding, with no apparent loss in power” tells me that you are asymptomatic during periods of a sudden rate drop which is certainly reassuring and makes me think too that this might be caused by your monitor not accurately recording, especially in the presence of an irregular rhythm disturbance like ectopic beats or perhaps Afib both of which I believe you have.

I get sudden heart rate drops when I go into AFib with a rapid ventricular response when my device switches to a non atrial tracking mode to prevent tracking these fast rates which would push my ventricles too hard.   Mode Switch puts me into a 2:1 block pacing the ventricles once every 2 atrial beats.  I certainly feel Mode Switching and am unable to exert myself during these periods.  

When you go back to your clinic, you could perhaps ask for the total number of Mode Switches that have occurred to look for any high atrial rates since your last check and to hopefully correlate any recent rate drop responses to a particular Mode Switch event?  I would perhaps also ask for additional long term external holter monitoring to confirm your current arrhythmia burden since you have been complaining of a feeling of "faintness" recently too.  

My feeling is that this is arrhythmia related and that your settings may be automatically adjusting to control these events and this is perhaps interferring with your home monitoring.  My home monitors frequently error in the presence of an arrhythmia particularly with rapid automatic Settings changes (like Mode Switch), so I always feel my neck pulse to confirm what is happening during these periods.

I hope you continue to feel well and to achieve your exercise goals despite your sudden rate drops.   Please update us whenever you can and good luck

Experienced something similar

by MPS - 2023-05-18 12:09:57

For about a year I had the same problem. I'd be on my exercise bike in the basement wearing my Polar M430, which measured my heart rate on the wrist. Now and then it would simply lose contact with my pulse and drop down to around 70 bpm. I knew it was inaccurate because the heart rate monitor on my handlebar grips was still reading about 125. Nothing I tried changed this occasional loss of contact until someone recommended that I get a chest belt from Polar that connects to the M430 via Bluetooth. That solved the problem.

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