Garmin and Stryd measure/estimate VO in a different way.
It doesn't matter how they are measured if the end result is the same. For example, on my last run, both Garmin and Stryd have my VO range as 6.8. I've found that VO is identical with all my runs when using both my HRM-Tri and Styrd together. So, if the final results are identical, then the placement and data of the VO sensor around the torso isn't the reason for the 30% difference using Garmin Power. Are you using either the HRM-Tri or Run along with your Stryd and getting different data?
I just read a post in the 645 forum that leads to this additional question. If Garmin has a 30% higher running power number with the HRM-Tri/Run because it's located at the torso as suggested, does the 30% "disappear" when using a standard chest strap and a Garmin RD pod?
If Garmin has a 30% higher running power number with the HRM-Tri/Run because it's located at the torso as suggested, does the 30% "disappear" when using a standard chest strap and a Garmin RD pod?
I compared GCT and VO from HRM-Tri (with Epix) and RD Pod (with FR935) together on the same runs a number of times. GCT from RD Pod was ~ 20% lower, VO was roughly the same. I could only compare RP from different runs done with either HRM-Tri or RD Pod. The GCT difference remained ~ 20%, while running power did not look markedly different. So the difference in GCT did not result in a difference in RP, in this limited set of datapoints. Which doesn't permit a firm conclusion.
Grant it, this is an extremely small comparison, but the use of a Stryd, Garmin RD pod, or HRM-Tri all producing the same vertical oscillation data tells me the 30% difference the Garmin Power app is displaying is not related to VO being measured from the torso rather from the foot. It would be nice to know how the Garmin Power app is actually calculating power. I would think "power" would be a standard measurement; much like HR. As of now, Stryd and Garmin Power are two different animals. Imagine trying to train in HR zones if product "A" and "B" had a 30% difference. I'm not familiar with cycling power meters, but I wonder if there's such a discrepancy with different cycling power meters also?
Power is power but the method used to estimate it is the difference. Clearly Stryd and Garmin empty different methods. The only issue with having different methods is when you choose to compare them or, attempt to train using the different systems. As long as the system you use, be it Garmin or Stryd produces reliable numbers with good precision then it doesn't matter; except for bragging rights of course. The problem of course is when you try to train using both.
There are differences between cycling power meters too.
Correction: earlier I wrote that VO was the same when comparing RD Pod and HRM-Tri, based on about 5 runs with both devices done last year. After posting I did one run with both, and this time VO from the HRM-Tri was 19% higher and GCT was 6% higher than the value from the RD Pod. Never believe stuff you read on some interweb forum, not even when you wrote it yourself. And before submitting this utterly unusable statistic to the Journal of Irreproducible Results, I'll do a couple more comparison runs in the coming week.
The only issue with having different methods is when you choose to compare them or, attempt to train using the different systems. As long as the system you use, be it Garmin or Stryd produces reliable numbers with good precision then it doesn't matter
I was using Garmin Power with my HRM-Tri prior to getting a Stryd. I switched to Stryd for my power data, but continued to use my HRM-Tri. That's when I noticed the difference in power numbers, but the data provided by the two was basically identical. I've disregarded the data from Garmin Power and use Stryd now. My inquiry is more out of curiosity on how Garmin was calculating power and why there was a difference. Stryd basically paved the way for running power and unofficially set the standard on how it was measured. I would have thought Garmin would have followed suit. It reminds me of the old VHS and Beta days. I just think having a power "standard" would just be easier for everyone. If that standard were the same I wouldn't care if Garmin used 5x2=10 and Stryd used 7+3=10, as long as 10 (power in this case) was the end result from both.
having a power "standard" would just be easier for everyone
Couldn't agree more. But as long as manufacturers have proprietary methodologies, then we are unlikely to see a standard. Running power is only ever going to be 'guesstimated' as there is no really direct way to measure any of the forces being applied. At least cycling you can measure force applied either at the crank, pedal or hub.
In the meantime, I'd recommend just using one system. As long as the numbers are precise and meaningful, the magnitude of the number doesn't really matter.
I may have found why there's such a difference between the power readings from Stryd compared to the Garmin Power app assuming they are both using the same metrics for their data. The following link is what Garmin uses to calculate their power readings.
Here you'll notice that Garmin uses speed (pace) from the watch to calculate Kinetic Power, Horizontal Oscillation Power and Wind/Air Power. That data comes from GPS, which is inferior to speed (pace) recorded from a Stryd pod which doesn't use GPS. It's my belief that if the same metrics are being used to calculate power, then the differences seen between the two is due how speed (pace) is reported. Maybe I'm beating a dead horse. Perhaps the two are just using two different equations resulting in two different power numbers and I'm spending way too much time thinking about this.
