How reliable is new wrist based power on Garmin Fenix 7

Literally the post before you states that power is an imaginary number without any consensus between different companies and you write this?

I put my stryd for good away and are happy with nativ garmin power, one less device to charge, one less subscription to pay and one less app to use.

Yeah I think what people need to realize is that there is no accuracy with power meters when running because there is no agreed upon way to measure it.  Therefore, what you want is precision and consistency so you can use it as a metric for training.  Whether I use Garmin power which states my power at 450 watts during intervals or Stryd which states 300 watts, the key is that these readings are repeatable so next time I know what my targets are.

*Insert joke about Brain Power*

tboooe said:

I think what people need to realize is that there is no accuracy with power meters when running because there is no agreed upon way to measure it

This is correct.

Both Stryd and Garmin attempt to model the metabolic power (ie the energy that the body is spending) when running.

Both are using 3D accelerometers:

- horizontal power: linked to moving the body forward, including the small energy loss due to the foot hitting the ground,

- vertical power: the body moves up and down

- lateral power: energy spent/lost through lateral vacillating.

Finally, both vendors use external data (altitude and wind) to account for external forces (gravity and wind resistance) to the result.

I have been reading the available documentation and additional resources (links below if you are interested) and I have not identified why the absolute values are different. My assumption is that Garmin and Stryd use different running efficiency assumptions to transform the 3D data power into a metabolic power number.

There is no documentation on that transformation. Some papers use an average efficiency for running and divide the 3D power by that efficiency to get to the metabolic power. It is possible that the vendors have a more refined model with different conversion factors for each of the 3D components: that could explain why the difference varies depending on pace, etc.

Stryd power overview

Garmin power overview

EESA 3D approach for total external power for running

As it has been said, both approaches are valid and work: predictable, repeatable and accurate (in the sense they correlate to each other and to other lab force plate measurements).

They cannot be compared from a value perspective though. It would be a bit like comparing gas mileage expressed in gallon per miles with gas mileage expressed in liter per 100km.

FYI: there is at least one other running power model: the GOVSS model uses a reference "lactate threshold" power calculated based on a formula with the lactate threshold speed, uses actual speed, air resistance and slope to calculate real-time metabolic power directly.

Gravity Ordered Velocity Stress Score (GOVSS) model for running analysis

Bernie said:

I have been using Stryd for a couple of years and the last weeks I compared the power between Stryd and Garmin for over 20 runs (compared km or interval averages), long runs, intervals all kind of runs with a wide range of power. I find a consistent factor of 1.4 (correlation >0.98) (Garmin power = 1.4 x Stryd power). This is good enough for me to stop using Stryd. 

I get something very similar at 1.3 multiple on flat roads at greater than 9:00 min/mile pace.  Once I get on inclines or hills or do intervals, Garmin power increases much more than Stryd and the multiple is 1.45.  Either way its consistent so Garmin Power is good enough for me.

I disagree too. Some of the best flat marathon training is done on hills...

I want to revise my comments a bit.  After reviewing more data I find that Stryd is more consistent and is able to reflect increases in pace/effort better than Garmin.  For example, today I ran an 8 mile tempo run at 15 secs/mile faster than last week.  Running along the same stretch of road, Garmin actually measured today's power as lower than last week even though i ran faster.  Stryd on the other hand showed I was running with about 5W more power.  

Are you sure all settings are the same? Is your weight setting the same. If so, is the Garmin setting to take wind into consideration on or off?