The garmin and wahoo straps measure the electrical signals from your contractions, while the watch measures optically. Since they both exhibit this phenomenon it's probably something your body is actually doing vs. just being sensor errors.

If you were having tachycardia episodes, you would probably feel it (general weakness, etc.); so that seems less likely, but the MDs can weigh in.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

I've had the same issue occur (twice last week), and making sure my chest and the strap were moist/wet when starting also didn't necessarily solve it. On the bike however it never occurs, only when running. It seems to lag a bit in the beginning and then it shoots up to threshold heart rate or way higher values then I've ever managed in races or lab tests, whilst running very easy long run pace. Seems almost as if it tries to lock onto my running cadence instead of my actual heart rate. After a few 100 meters it did stabilize again to normal values. Garmin Forerunner 920xt and had it happen last winter with a different HR strap than this one.

Do you mean it happens also with the optical watch sensor?

Generally, the optical watch sensors do not work so well especially during sports.
What the straps are concerned, if you do not sweat yet they work often badly.
Furthermore, you have to exchange the straps regularly. I use cheap polar straps, the Garmin sensors fit on those.

Like above said, I replaced the Garmin strap with a polar. But even then it sometimes can happen.
Make sure the skin is wet. I also wet the baselayer in the area where the sensor sits.
Also windbreaker eg can interfere the data until you are kinda soaked.

But just to make sure there isn’t anything serious you should get checked by a cardiologist.

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-shoki

Optical sensors of the kind mounted on Garmin watches do not work very well for most people. The primary limitations are battery-related, so the lights are not bright and the location of the watch on the wrist. (movement of the wrist and less flesh)

However, my Polar OH1+ optical sensors works brilliantly. It has more lights and a tighter fit on a more "fleshy" part of the body makes all the difference in the world compared to the watch-based wrist sensors. I wear my just below my elbow; it's comfortable and has been perfectly reliable.

I will be buying a Polar HR strap(V10 or H10...something 10...can't remember) so that I can gain reliable HRV data, something the OH1+ can't do. (I share this strap with my wife for Zwift on Apple TV...she thinks my sweat is gross and wants to minimize her contact with it!)

Electric pylons and electric junction boxes can interfere with the HR sensor.

Could that be a factor?

I've had similar issues, but only with the Wahoo and Garmin 935. Spikes, connection drops, and sometimes also low readings (HR in the 50's during a run). Never had these issues with Garmin straps, but I had 3 Garmin straps die on me before they were a year old, so I recently switched to a Wahoo one.

I experience the same thing at times with my HR strap (and Garmin Forerunner 220 without optical sensor). It's common. My theory is that electric connectivity is poor when the strap is freshly put on, especially on cold days, on a dry chest.

Louis :-)

Good point! This used to happen to me when I would run near a transformer. My HR would read "220" until I got away from it.

This will impact transmission (I get similar issues with my PM and other sensors), but won't impact HRM in the watch (unless the watch is being used as a remote device and the recording is happening on a cycling head unit).

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

this is pretty common at the start of a workout, when dry skin can lead to poor electrical contact between skin and sensor, and the sensor picks up on false electrical signals. Generally the readings are high (200-240) then settle down 5-10 minutes into a workout as your body begins to sweat. Situations that can exacerbate this are:

* cool and low humidity conditions
* an older belt, where accumulated salts from sweat provide an alternative electrical pathway
* the technical fabric of some running shirts and jerseys are more prone to static electricity, that can create false electrical signal to the chest strap.

Actions you can take:

1. Moisten the skin and sensor pads before your workout.
2. Wash the strap weekly (or even more frequently?) to prevent salt accumulation.
3. Replace the chest strap every 12-18 months (just the fabric strap - you can keep the sensor unit and switch it into the new belt)
4. Turn off HR autodetect on your watch/head unit to prevent it from resetting zones.
5. Try to work out which of your shirts are more prone to static electricity.

It's your lucky day!!! (Why is it? It seems like I'm the only one who knows this...)

Here's what you need: Spectra 360 Electrode Gel from Parker Laboratories.

It's medical grade stuff (for professional use only) I'm an amateur, but don't tell the Parker folks :-|

Anyway, rub a few drops under each electrode pad and I promise accurate readings from the start to the finish of your workout.

It dices, it slices, and it really really works!

Google it, it's cheap. 8.5 oz will last me way longer than a year.

Tell 'em Pat Summerall sent ya. (nobody's gonna get that :-( )

Enjoy the HR Journey - accurately!

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I saw this on a white board in a window box at my daughters middle school...
List of what life owes you:
1. __________
2. __________
3. __________

I was having similar HRM behavior. I found this thread after a search. Here is some HRM data in question ( the time scales are similar, but the HRM levels are off a bit from test to test):

I have not tried the gel as mentioned, I just lick the detector pads. I was a little concerned with the initial spikes but now I'm thinking that it may be due to shirt static prior to sweat moisture and the onset of actual sweat that improves the signal transmission. I have not tried the TICKR while on the treadmill (it's Bluetooth and my Garmin watch is ANT+ only) so I don't know if the same would occur.