Site icon the5krunner

Garmin Running Power :: Garbage In…Garbage Out?


FTC: Affiliate Disclosure: All links pay commissionReading Time: 6 minutes

I quite like the Garmin Running Power app. It installs well, is nicely configurable and seems to run awesomely in all its bug free glory.

But is it showing complete garbage?


I had a little play on Sunday, comparing Garmin Running Power (GRP) with RunScribe and STRYD. Here are the thoughts and results of that day’s runs, where I looked a little at VO and GCT.

Knowing that the Vertical Oscillation (VO) and Ground Contact Time (GCT) are inputs to the power model, my takeaway thought from Sunday was “BUT what if the sources of VO/GCT were either wrong or inconsistent or inconsistent between source devices?” For example I used the HRM-TRI as a source of GCT and VO but what if, instead, I had used an older, compatible HRM-RUN or an RD-POD? The HRM-RUN might have the same firmware but I doubt the RD-POD would produce the same values for GCT and VO due to it’s position either on the foot or on a waist belt.

Today I also thought “What if I use STRYD as a source of pace?” and “What if I use a Garmin footpod as a source of pace?” and “What if I use GPS only as a source of pace?” and “What if I use GPS+GLONASS as a source of pace?” and “What if I used the Milestone POD as a source of pace?” and “What if I used a Fenix 5x’s GPS as a source of pace rather than the 935’s GPS?”

Anyway. You can hopefully see where I am going with this. I’ll just cut to the chase and tell you what I did as I don’t quite have access to all that kit.

What I Did

I used a variety of different sources of pace to see how the different accuracies of the pace sources affected the GRP estimate of power around a running track in windless conditions.

After a 15-20 minute warmup (also a GPS warmup) I did one mile at about 5:00/km and then one km at about 4:00/km. I had a break between those intervals to check/swap pairings and sources of pace data. I then changed the PACE SOURCE and repeated the 1mile+1km.

What I expected

Previously I have found Garmin’s pace accuracy is repeatedly not great compared to other brands. Maybe you have found otherwise? The 935 is, however, one of the better Garmins, IMHO.

Contrary to the received wisdom, I find GLONASS does NOT help with running pace accuracy in ‘open sky’ conditions like today on the track. Maybe you have found otherwise?. So I expected a notable difference in the resultant POWER reading when using a footpod as a source of distance/pace.Not necessarily better…just different.

I find STRYD a good source of pace and distance even when not calibrated. Others find the same. And I find the Garmin pod is alright for pace/distance when calibrated (today it was not calibrated…it didn’t auto-calibrate on for some reason…sorry!)

I expect a 935+STRYD will produce a better power figure than 935+GPS and I suspect 935+GLONASS will be worse still. I expect the 935+footpod to be closer to the power from 935+STRYD. ‘Better’ could mean that the power number is higher or lower, I suppose, I don’t know the maths. I would guess that a 935+STRYD based pace figure would have less variability and would result in a lower power I say, a guess.

Kit Combos I actually used

  1. Garmin Forerunner 235 + RunScribe
  2. Suunto Spartan Sport + STRYD (STRYD also caches the data)
  3. Garmin Forerunner 935 + Running Power App
    • with Garmin Footpod (uncalibrated)
    • with STRYD (uncalibrated)
    • with GPS only
    • with GPS+GLONASS

What I didn’t do


These findings might prompt someone into a more rigorous analysis.

Just imagine that I believe in the Flat Earth, fairies and Jedi Knights and take my findings with a pinch of salt. Maybe a larger pinch than you might normally take, but a pinch nevertheless.

Heads Up

STRYD data on the Suunto SPARTAN is the control data for each of the 4 combinations of GRP

I’m NOT saying STRYD is right but in my experience it is repeatably consistent for me and if it can’t be repeatable on a track with no wind then….eeesh.

So, what we are looking out for is the variance to the STRYD power on the 4:00/km kilometre and there will be a bonus on the 5:00/km mile section before that if it shows something interesting.

RunScribe power is in beta. So I won’t discuss that much.

Also note that on the 5:00/km bit my mind may have wandered off with the aforesaid fairies somewhat. And my pace may well have varied accordingly 😉 I’ve not yet looked at the data as I write this but, from memory, I expect the pace was 3:50-4:05/km apart from the first 100m of each of the faster kms as I was a bit more excited at that point. That’s not to say how rubbish or wonderful I am just saying that it was consistent enough for the purposes of this post, in my opinion.

Result 1: GRP Pace Source: Garmin Footpod (uncalibrated)

Note the colours of the lines might refer to different devices in subsequent charts…sorry.



Result 2: GRP Pace Source: STRYD Footpod

Note it seems that the 935 took 2 minutes to connect to STRYD. My bad, probably. It never normally does that. I ‘ll just use the section where STRYD pace is recorded.


Result 3: GRP Pace Source GPS

Result 4: GRP Pace Source GPS+GLONASS


Result: Summary Table

IF you assume STRYD is most accurate (my personal bias). Then the 935+STRYD combo is the closest to standalone, raw STRYD data in the Suunto SPARTAN. Next comes 935+GPS; next closest comes 935+GPS+GLONASS; next comes 935+ Garmin footpod (uncalibrated)

I think the uncalibrated nature of the footpod is a problem. My bad. (I had planned to use the MilestonePOD over BLE but couldn’t get it to pair with the 935 even with a new battery)

It seems that, as the pace inputs become more accurate, then the closer GRP power comes to STRYD power. Again, I’m not saying STRYD is right.

Distance/Guide Pace Mile (@5:01/km) Km (@3:47/km)
Average Average
GRP+Garmin Footpod 346 448
STRYD 238 304
 GRP as % of STRYD 145.38% 147.37%
Distance/Guide Pace Mile (short @4:42/km) Km (@3:48/km)
Average Average
GRP+STRYD 345 421
STRYD 255 310
135.29% 135.81%
Distance/Guide Pace Mile (@4:54/km) Km (@3:57/km)
Average Average
GRP+GPS 345 434
STRYD 247 301
139.68% 144.19%
Distance/Guide Pace Mile (@4:54/km) Km (@3:57/km)
Average Average
STRYD 250 309
144.80% 145.95%


Raw Data

Data Files are here: in 12Dec2017 folder. They shows lots of circles of St Mary’s running track. The files may contain grossly wrong oHR data.

Other Garmin Running Power ‘Tests’

Summary & Thoughts

I’m not surprised.

I wouldn’t be surprised to see different numbers again with an RD-POD. I don’t have an RD-POD.

Both the GRP and standalone STRYD seem to produce broadly similar power lines. Similar in terms of their trend and variability but not in terms of their magnitude. On that basis you might superficially call either of them believable. If someone wants to analyse the data sets that would be cool (see above).

If you are thinking of trying the freebie Garmin Running Power, then I would make sure you are happy with your source of pace/speed. Furthermore I would also make super sure that you use the same sensors forever more. If you don’t your power numbers will change, I reckon, and you REALLY don’t want that to happen.

This interestingly throws open a new market for STRYD. If they can release a cut-down, cheaper version of STRYD that just outputs pace/cadence/stride length then they ease their way into the Garmin Running Power environment. Let’s face it, you wouldn’t buy a full-priced STRYD and then not use STRYD’s power metric. Such a new STRYD just focussed on accurate pace would, for sure, also attract quite a few runners who have almost zero interest in power but about 98% interest in accurate pace.

Just a thought.

Reader-Powered Content

This content is not sponsored. It's mostly me behind the labour of love which is this site, meaning it's entirely reader-powered content ❤️ I'd really appreciate it if you'd follow, subscribe or Buy Me A Coffee ❤️ Alternatively please buy the reviewed product from my partners (which costs you no extra) and, for that, I receive a small commission. Thank you! FTC: Affiliate Disclosure: All links pay commission. As an Amazon Associate I earn from qualifying purchases.
Exit mobile version