In your videos Eric, you often mention watts. A foot pod is it really useful or it remains a gadget for non elite runners (I know Jim Vance use power metric for his training plans)?

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Great question Fabrice.  I think watts are extremely useful for assigning effort on trails. I have coached with power for years in cycling and I use power in coaching many of my ultra athletes.  I will be making more watt/power driven training plans in the future.  I have been testing out the technology (Stryd) and wanted to be sure of the accuracy, which was not there a few years back.

Just like with other metrics (HR/speed) it is only useful if you know how to implement it and use it.  So I highly recommend watts, in conjunction with HR and speed.  I use all three based on the purpose of the day for my athletes.

Hope this helps.


For a basic implement I suppose it is possible to record watts value for different speed/HR zones on flat terrain ?

Maybe a new chapter for the next The Cool Impossible. Thanks for your answer :)

I will be doing more videos on watts and training plans, which I think will be more effective than a new book!

But YES, if you have The Cool Impossible, use the One Mile test chart to design your watts - using the avg watts for your one miler.

If you decide to let me know and I can help you make this conversion.

I'm doing the 10th week of the first phase of cool impossible. I will redo test soon. I'll let you know it. Thanks for this cool offer. 

Even if you live in a flat area without hills, the Stryd has a benefit in providing improved accuracy for pace and distance vs. GPS:

I did a comparison of Stryd vs. GPS earlier in the year, using a surveyor’s wheel as a control measurement.

Control = 0.653 miles

Stryd Lap 1 = 0.64 miles

Stryd Lap 2 = 0.65 miles

Stryd Lap 3 = 0.65 miles

GPS Lap 1 = 0.71 miles

GPS Lap 2 = 0.69 miles

GPS Lap 3 = 0.69 miles


The control lap is likely a little higher than actual.  It was difficult to keep the measuring wheel on a 100% true path due to variations in the road surface.

Actually deviated 1 to 2 feet from part of the path on Stryd lap 1 (daydreaming), but it certainly wasn't 0.01 miles (53 feet) of deviation.

Above Stryd laps are with a 100.0 calibration factor.


Uncalibrated Stryd distance is significantly closer to the control distance than the GPS distance (on this course).  GPS distance is significantly higher than the control distance (on this course), and thus pace is significantly faster with GPS than uncalibrated Stryd.  I predict that GPS would be much more accurate on a course with more straight lines and less curves.

This test indicates GPS measures over 6% further than the control (on this course).  Perhaps some increased Stryd calibration factor is warranted since the Stryd distance was a small amount less than control; it is difficult to say absolutely without a longer control measurement / longer sample size.  However, the control distance is likely slightly higher than actual, so the Stryd is likely spot on without the calibration.


Stick with Stryd for distance and pace.

Leave the calibration factor at 100.0

Thanks for all this theory crafting. I'm impatient to receive my stryd and test that :) 

Love this info, thanks for sharing. 

I should have mentioned: To get this accuracy advantage, you'll need to set your watch to always use the Stryd for pace and distance, and not all watches support that.  (The Garmin Fenix 3 does.)

More info: https://support.stryd.com/hc/en-us/articles/360002439534-Garmin-Wat...

I do not think it is possible with Suunto.


As planned, I come back after my mile test. I did it 20'' faster than previous test (thanks to the cool impossible) in 7'35'' with an average power of 313w.

After two weeks, I find power datas usefull and I'm willing to use them in the next phase of training :) 



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