Every so often, I'm motivated to test concordance between various sensors that connect to bike training devices. This is usually to confirm that there is good consistency between devices, usually power meters. This particular test aimed to evaluate some HR sensors and a couple of power meters. I wanted to compare the HR derived from my Garmin Vivoactive 5 watch (optical), a Polar Verity Sense armband HR sensor (optical), and my regular Polar H10 chest strap HR sensor. Over the years, I've found that Polar chest straps set the standard for HR measurement, and they are good tools for measuring heart rate variability (HRV) via the HRV4Training phone app. Unfortunately, I have been experiencing some skin irritation from from sweaty chest straps during indoor training, so I wanted to evaluate whether switching to one of the optical sensors might help.
As a secondary aim, I was interested to see how my current trainer, a Garmin Neo 3M, compared with a pair of Assioma Favero dual sided power meter pedals.
The set up
I was set to conduct a workout using ERG mode on the trainer. Neo trainers report actual power, not an idealised power from the workout file. I stayed in the same gear throughout the workout. In the event, accumulated training fatigue and lack of time (and boredom) meant I cut the workout short.
I use an Apple TV to run Zwift. It was linked to the Neo 3M trainer for power and cadence (and was controlled by the trainer). HR was derived from the Polar Verity Sense arme band sensor.
I collected power and cadence data from the Assiomas on a Garmin Edge 840 computer, along with HR from the Polar H10 chest strap.
Finally, I usd my Garmin Vivoactive 5 watch to collect HR data using it's built-in optical sensor. No ther sensors were connected. The Vivoactive 5 isn't a particularly full-featured watch, and is perhaps more of a leisure/lifestyle watch and doesn't have the latest model of optical sensor.
Data files were downloaded from Garmin Connect and analysed using the DCRainmaker Analyzer web app. Note that there will be a a random offset of a few seconds between the three devices since I can't start them all exactly synchronously. [For all graphs, click on the image for an enlargement]
Comparison of Heart Rate sensors
I was actually quite surprised by how well the three sensors compared. Blue is my Polar H10 Chest strap, red is the Polar Verity Sense optical sensor work on my forearm, while green is the Garmin Vivoactive 5 watch. Overall there's a very good match between the two Polar sensors. Both optical sensors seem to twitch out of alignment with the H10 from time to time, with a bit more deviation in the case of the Vivoactive 5. The average HR is very similar.
Looking a bit closer at the traces, there seems to be a slight lag when the optical sensors are compared with the H10, though It's within 'experimental error' I reckon. In the panel below, you can see one of the Vivoactive 5 'twitches'.
I'd be quite happy using any of these sensors in my workouts.
Comparison of Power Sensors
I generally do all my indoor training to power levels, and so I do worry whether the trainer is accurate in relation to my bike mounted power meters. On my time trial bikes, I use either Assioma pedals (dual) or a Powertap hub, depending on which bike I'm using. I have occasionally run comparisons between these on the road and find good concordance. Maybe it's time for another check.
For this test, I'm comparing the Neo 3M trainer (via Zwift) with the Assioma pedals (via the Edge 840). First up, here's the overall power picture.
This looks pretty good, with the two power meters well within 2W of each other. Here's a zoomed in graph.
Again, this looks pretty good to me, within about 1.5W (0.7% or thereabouts). I'm pleased a reassured by that.
Comparison of Cadence Sensors
I compare cadence sensors out of interest - I don't really pay much attention to cadence except where specified by by training programme. While I can see that pedals might be pretty good at measuring cadence, I'm not sure how an indoor trainer does it. How do they compare?
That looks surprisingly good. And in a close-up view, just as good.
Conclusion
For all three measures - power, HR and cadence - teh sensors are in pretty good agreement. Yes, the optical sensors may look like they have a little lag, but it's only a second or two and probably insignificant in the bigger picture. Similarly, the occasional twitch in the optical sensor graphs isn't I think significant.
So, all in all, I'm quite impressed by these comparisons. I'm now wondering about using the watch to broadcast HR to the turbo, and that'll feed into my next comparisson test, when I plan some short HIIT intervals.