Home› General Training Discussions

Running with Stryd on the treadmill - weird data

John KatsoudasJohn Katsoudas
in General Training Discussions
I'm posting my question here so as not to further bog down the RDP Groupme chat.

I did my first run on a treadmill in the gym today using my Stryd power meter and the Zwift app running on my iPhone.  I was also using my Forerunner 935 in parallel (using the Connect IQ Stryd app) so I could capture lap pace/power splits since I was going a B-A-A run.  The Stryd was paired simultaneously with the Forerunner 935 and the iPhone/Zwift.  

Almost immediately I noticed that the pace that the 935 was showing was almost a min/mi faster than what the treadmill was set to. Oddly, the pace being reported in Zwift was almost spot on with the treadmill.  I ended up pacing the run by treadmill speed rather than the pace reading on the 935, as it seemed the more realistic of the two.  At the end of the run I got two files downloaded to Training Peaks:  one from Zwift and the other from the 935.  The two files match exactly for average and max power (193/226) and TSS/IF, but distance is way off (6.73 vs 7.40 miles), as is avg. pace (10:34 vs. 9:41).  The Zwift data plot also has far less variability than the 935 plot, both for pace and power.

Since the pace/power source is the same for both (Stryd) I can only assume that the 935 is treating the data differently than Zwift is.  Any idea what may be causing this discrepancy?

The run was as follows:

40' at z1 (10:45), then 3' intervals of B-A-A @ 10:20, 10:00, 9:40 (I screwed up and did A-A-B, and the treadmill only had 10" increments for pace.  My TRP is 10:04).



Zwift data:








Forerunner 935 data:






Comments

  • John KatsoudasJohn Katsoudas
    BTW- I don't think heat played a factor, but it was hotter than hell during the run  B)


  • Mike WestoverMike Westover
    I wonder whether the 935 was getting pace/distance from its internal accelerometer rather than Stryd. That would explain why the watch and phone were giving you such different values. If you haven't already, you might want to set the 935 to use Stryd as primary for pace and distance (choose Stryd in the sensor settings and it should be one of the options).
  • John KatsoudasJohn Katsoudas
    Thanks Mike.  I made the assumption that, since I was using the Stryd Connect IQ app o the 935 and not the regular running mode, it was using the Stryd as the data source but it's best not to assume these things.  The other option that I considered afterward is this:  When I got on the TM I started up the 935 and it found the Stryd footpod.  I then started Zwift on the iPhone and paired it to the Stryd.  I wonder if, at that point, the Stryd disconnected from the 935.  Next time I'm on the TM, I may try the Stryd/935 first (without Zwift) to see if it's any better.
  • Mariah BridgesMariah Bridges
    Ive seen multiple people on the Stryd Community chat about this.... Never stuck around for the answer but you might want to hunt it down. 
  • John KatsoudasJohn Katsoudas
    Thanks Mariah!  I'll check it out.
  • Rafe ArmstrongRafe Armstrong
    edited October 30, 2017 11:58AM
    I'm a little late to the party on this question and don't have your exact answer but can provide some insight.  I haven't used Zwift but I have use the Stryd app and I know when I am using the Stryd app I cannot pair the Stryd pod to my Garmin at the same time.  I will bet the speed difference is because the Garmin was using the watch to estimate speed as Mike W alluded to above.  What I typically do with treadmill workouts is that if I am doing a flat workout I will use the Garmin only for simplicity.  And if I am doing a hill workout on the treadmill I will use the Stryd app because it will allow you to add incline which will give accurate power data on the treadmill otherwise the Stryd pod cannot recognize incline on a treadmill.  One more tip I have learned.  When using the Stryd outside, if you want to use it to record distance rather than GPS on the watch, you need to turn the GPS on the watch off.  If you just go into settings and tell the watch to use the Stryd for pace and the GPS is still on, the data will bounce around a little and you have to use different calibration numbers.  For example with my watch, if I have the GPS on but tell the watch to only use the Stryd for pace, I have to calibrate it to 100.4 and the pace curve is not as smooth. (I'm guessing it is still bouncing between GPS and the Stryd even though I told it to use the Stryd). If I have the GPS turned off then the watch tells me I am running much too fast at that calibration.  I have to decrease calibration to 99.5. Doesn't sound like a lot but it is.  BTW, once calibrated it is extremely accurate on pace and distance.  Also responds much quicker than GPS and I have gotten to where I almost always use the Stryd for pace/distance even when outside. As an example I did a 4 mile out and back today and at the finish it was within a few FEET of the starting point between the 2 miles out and the 2 miles back.  Another BTW, if you are using Training Peaks with power running then it calculates your TSS base on the the power not the pace so it really doesn't matter if the pace is off to get accurate TSS.  But it always helps my mind to know the pace data is right also :)
Sign In or Register to comment.