VO2 max/Perf Cond in Ultratrac /GPS off mode+Stryd always for speed/distance?

Training Effect and Training load do not need GPS as it is purely done on time and intensity. VO2max only works in the normal run profile (not trail running) with GPS enabled and sufficient GPS coverage. There is plenty of information on the Firstbeat website and this forum about what the VO2max algorithm is looking for in terms of reliable pace and HR information.

In normal use the 935 uses about 5% per hour of GPS activity and 5% per day for 24h heart rate monitoring. So even if you use GPS 2 hours a day the watch will last 6 days or so. What kind of activities do you get involved in that won't allow you to find a moment once every couple of days to recharge the watch? I (like many on here) have been wearing the 935 24/7 (apart from recharging, something I do when I am sat down at work so I do not miss out on any of the statistics the 935 provides) since the week it first came out. I have never run out of charge.

Thanks for the feedback.

I was aware that Training Effect and Training Load/Status do not need GPS (although Status needs occasional updated VO2 max in the preferred activity) and about the estimated battery use in 24/7 use of around 5 to 6 days at 2 hours a day of GPS activity and about VO2 max in normal outdoor run only. Hence I did not ask about these.

I was just confirming if and wondering why GPS was still needed if Stryd is giving reliable pace and why not then get up to 10 days per charge of 24/7 and 2 hours of Stryd running activity a day.

i guess you are confirming that even with a GPS accuracy equivalent footpod, for some reason you need GPS on to get VO2max even though the Stryd is supplying the speed and distance data for VO2 max and the GPS is redundant.

Is there any specific reason or is it just a legacy of assuming GPS was the only accurate option for speed and distance input into VO2 max?

If I were to hazard a guess at why Garmin wouldn't allow use of a Stryd pod for pace/distance info for Vo2Max calculation I would say that it's because they would then be relying on a variable they don't have any control over. Similar to why they don't do Vo2Max on treadmill runs even if you're using one of their foot pods for pace since the calibration factor can be tweaked by the user which if done incorrectly can throw the calculation way off.

I agree with many of the points in this thread - Stryd probably IS accurate enough, but I don't expect Garmin to allow VO2Max from 3rd party sensors anytime soon. (And the cynic in me suggests Garmin are trying to #$%^ Stryd over with ANT+ reception and duplicating running power, so they aren't going to want to do Stryd any favors anyway).

And the battery life of the 935 is pretty massive - even if you are running 12 hours/week with GPS on at 1s intervals, you still probably only have to charge once per week.

Hi folks,

I've been super busy lately, so apologies if this is a bit scattered.

The short answer is, yes, in theory it would be possible to use movement speed data provided by a Stryd, or Stryd type device as the external workload variable for the Firstbeat VO2max / Performance Condition analysis. There are already quite a few devices, even some from Garmin, that utilize accelerometer derived speed data - the Vivosmart3 is a prime example. You'll even find some non-GPS watches that 'borrow' GPS data from a paired smartphone for this variable.

That said, at a design level, someone would need to anticipate the use-case of collecting movement speed data from an external source, figure out how to work with the data and how it arrives from that configuration and all of that technical work. For the vast, vast majority of folks out there, the movement speed data from their GPS watch is perfectly a-ok for their needs. That's what's expected and planned for.

But for example, there is a potential use case out there where someone with a FR935 might want to grab GPS data from their iPhone - why, I don't know, but someone might - for some reason - want to do this. Naturally, the pieces are there, and it's possible in theory, but almost certainly isn't something that's expected.

Nothing particularly sinister... just a question of what you expect and plan for, I'd imagine.

Hi All...Thanks for the feedback.

My conclusion from the feedback...is that the GPS only rule is an historic relic that (validly pre Stryd and still valid for other pods) assumes GPS is the best pace input for VO2 Max and if the watch has it, it makes no sense to use any other source like a footpod which is perceived as less reliable....


Some concluding answers....forgive the length..as rather just post once...


On why not use GPS daily....

Answer....Do not mimd...Been doing that for past 3 years with Fenix 2 and 3 and 935. Was just curious as to why the VO2 Max rules in the 935...in 2017 had not caught up with the emergence of Stryd pod in late 2016....For example in 2017 ran 4100km...(4070 barefoot except last 30km of Comrades 2017).4050 with GPS...except the first 2 runs with Stryd on 30/31 December......Switched GPS back on on 1 Jan 2018 when I realised VO2 and P Cond were not updating....and have run 9 hours with it this week.

When you are running a similar menu of say 20 favoured route variations in say 3/4 cities (visiting Mum etc) for the past 20 years....(have done 19 consecutive Comrades and Two Oceans ultras) and you have measured them all umpteen times with GPS then why just have it on only to get Vo2/Perf Cond updates when you have a Stryd anyway giving you pace and distance in Garmin Connect and on watch.

When you are on the 400m track with a Stryd anyway...why have GPS on at same time just for VO2....VO2 from Firstbeat uses pace and heart rate ....The watch is getting both of these in same native run datafields without GPS....

Lastly am using Stryd barefoot....with 3 rubber bands for now. Not unnoticeable but can still run 30km without getting too distracted by it....so makes sense to use all its benefits....inclluding doubling the 935 charge time....but that is just a wish not a real dealbreaker.

Have done 2 *20km rums with both a Runscribe Pro and Stryd on same foot with rubber bands. Lucky the Stryd can sit low quite close to the toes versus Runscribe higher up.

By the way all my data is public in Garmin Connect...

On the outler use cases needing development resources...
Answer...Accepted but given that Stryd is giving the same pace output as GPS....then it is the same VO2max algorithm....it is not like the watch has to work out say a mew metric like power for VO2. Pace from Stryd is already there in the datafields.....Surely it is a minor change to enable it as the input if GPS is off.



Battery use update...

Have run with both Stryd and GPS this week...HRM run with Garmin power enabled....using an IQ watchface....no backlight...occasional bluetooth sync...notifications off..., 24/7....
After 4 days...am at 20%. Battery left.. with 9 hours of GPS/Stryd activities....so I am in the 5 day...24/7....11 hour activity benchmark....I am fine with charging every 4 days....

Quick side question/note
I noticed in the 2017 Two Oceans which was quite cloudy that the Fenix 2 lost the GPS track horribly at around 31km of 56...in the coastal climb up Chapmans peak....So the total distance ended up very wrong....I think the Fenix 2 struggled more with clouds and trees than the Fenix 3 but even then it worked well dor 95% of runs. Pity it messed up in a race....but was not pacimg with it....Just the distance and splits got stuffed in the database.

In the 2017 Comrades....with the Fenix 3.... and also with Fenix 2 in previous years.....you get a bit of GPS drift when you stop for a minute or two....to get a rub or a toilet stop...One obviously keeps the activity timer running....but it does mess up the splits and the overall distance slightly but noticeably....e.g. can add 1 to 4 km in an 87km race.

How is the 935 versus Fenix 2 and 3 in regard to drift during a 2 to 3 minute stop in a race that is gun to gun so the timer keeps running.?

Regards