New STRYD auto-CP calculation

stryd powerrace app garmin 235If you understand the title of this post, ie “New STRYD auto-CP calculation” then you will know that it sounds like a pretty cool and useful feature.

If you don’t understand the title then you will, no doubt wonder what on earth we are talking about 😉

Nutshell: Critical Power is your “forever power”, for most people it is supposed to be similar to your maximum 60-minute power (CP60) which is supposed to be the same as your FTP. For any given duration, say 10 minutes, you will have a different maximum power; your CP10 would be much higher than CP/CP60/FTP. So there really is a curve of critical power values across time.

Just knowing that can help you target a race PB, for example, by reading the power value on the curve for your target race time. But CP also directly feeds back into the calculation of POWER ZONES and training in certain power zones is a stimulus for producing physiological adaptations. ie you train in a certain zone and certain bodily stuff happens – you are faster, more able to go further or both #ItsComplicated (but important)

So it really is important, or even fundamentally important.

But it’s hard to work out the zones manually, as that can require you to follow a demanding test protocol. IMO, to better estimate your full CP curve over many durations, you would be best to produce maximal efforts over, say, 6, 30 and 180 minutes. And in reality, few of us are going to do that.

I’ve been advocating tools, like Golden Cheetah, that automatically calculate your CP. Now STRYD has integrated a similar auto-calculation of CP into their ecosystem. So there will be no more dreaded FTP-testing (CP-testing). Although, having said that, you will still need to get cracking and turn in some power duration PBs. In other words, you need to have ‘breakthrough sessions’ to cause a change in your CP value.

Many of us leave our good workout performances in our CP curve calculation for WAY too long. I think MarkL@GoldenCheetah said something like 21 days is the best historical time frame to use to calculate physiologically meaningful CP curves. I normally choose a couple of months worth of workouts for my curve. The point of saying this is that I don’t know what sort of decay factor STRYD have built in (although it looks like 3 months)

So what have STRYD done?

It looks like a fairly substantial addition to the platform, albeit simple to use. On the iOS/Android app all you have to do is to enable auto-calculation.


And then you can also choose if you want to be updated whenever a change to your CP occurs. I think STRYD may have missed a little trick here as I think they should notify you whenever there is ANY breakthrough and ANY POINT of your critical power curve I’m assuming that they will only notify you of a change to you 60-minute CP…CP60 but it is quite possible to have a breakthrough session at other power-durations without changing the CP60/CP value. Sites like can do that for you (for free) as well.

Once any of your workouts are updated on STRYD’s platform and your new zones recalculated, then I’m assuming that this will influence all of Powercentre’s calculations and insights (eg the intriguing Histogram). The missing piece of the jigsaw is that the updated zones can’t be updated on your Garmin as, err, Garmin don’t have running power zones.

Some points

  • This should be working for you NOW…go for it. Everyone should probably use it. Be mindful of not doing things like changing your weight in the app or linking to your weight in Apple Health (most people should not regularly update their weight setting with STRYD unless specifically on a weight loss program IMHO)
  • STRYD recommend periodically running near maximum efforts at 10-30 secs; 10-20 minutes; and 50+ minutes. I’d say that 1-2 minutes or, 5-6 minutes, 5k and 180 minutes would give more meaningful curves in other software packages from my experience. But I don’t know exactly how STRYD have implemented this so their recommendation might be best to follow.
  • STRYD seem to suggest that they look at the last 3 months of data and require at least 12 runs in that period
  • That then brings us back to how you can actually train or race in a power zone that has been auto calculated. hmmm. Someone should write a CIQ app or something. Let me see…


I’ll update the STRYD Review (aka STRYD Bible) and don’t forget there’s the new STRYD pod

STRYD Review, 10,000km Update – (Dual-) Running Power ⚡ Pod



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10 thoughts on “New STRYD auto-CP calculation

  1. Well, I enabled it and it messed up the zones.
    Just the day before the announcement I did an one hour run at 78%HRmax and 287W average.
    Yesterday morning when I read that announcement I got excited, hit the “auto”-button in the app and I was prompted with a CP of 284W. Well I guess I don’t need to elaborate why I think this is just not correct.
    I’ve over an year of data in powercenter, so it shouldn’t be the lack of data.
    I did a reset now and the algorithm will start from scratch again with upcoming workouts. If this doesn’t lead to reasonable CP-values I’ll just go back to the old CP testing from time to time.

    To be fair: I’m a trailrunner. Although I have some similar concepts in my weekly routine as a road-marathoners, I have to pay attention to other aspects (steep climbs, technical climbs/descends etc,) too.
    Most likely that messes up the algorithm because such activities do often not show a big raise in power values from Stryd which would reflect my RPE in those situations.

  2. I’ve been using Xert to analyse my running data, for the last 18mths and Xert was saying my TP was 321w, after the auto calculation, Stryd has me at 324? I’ll take that as 👍

    1. yep, I think Xert is AWESOME.
      Only reason I don’t use it in anger is that it does not properly handle triathlon ie bike and run (I know there are workarounds)

  3. To be frank, I never did any of their CP-tests, because, as you said, to get an accurate result you need to produce all-out efforts over prolonged periods of time. And who does that outside a race or without a gun to their heads? That said, I usually put in 5k/10k race times, and go from there. Zones, and paces never really lined up properly though, especially at thresholds form one zone to another. So I welcome this option and opted for it. My CP was adjusted a few points down (7 or so), and my runs yesterday showed a better correlation between power and pace. I’m more comfortable with an auto-detection system that looks over my recent training, easy runs, and quality sessions alike, even when it has me a little on the conservative side. Putting in a 5k PR where all stars aligned (because who doesn’t put in their PR 😉 ), and get skewed zones that my training status simply does not reflect, might very well lead to overtraining. I wished there was an option to exclude certain runs from the calculation. Especially now that it’s Summer, and I always run in >30°C temperatures my effort is quite a bit higher at the same pace/power. Runalyze does this with their effective VO2Max. I still have a v3 Stryd, does v4 take temperature into account as well or just head, and cross winds?

    Oh, and I am a supporter for good now. Actually, I thought I already was but you kinda lose track with all those subs these days. Keep up the good work! (And maybe keep a cleaner shop over at those boards, it’s not very encouraging to have discussions when half the topics are spam. 😉 )

    1. yup !!

      having said that, temperature might well be accounted for soon. If you look on the app when you enter a PB for the CP calculation it asks for the temp. So STRYD are clearly aware of the effect of heat/humid (hence the new pod sensors!!) (edit: but that wil likel be the effect on air density rather than the physiological effect)

      thank you to my latest and greatest supporter.

      I’m not sure about the bulletin boards. I have max anti-spam working AFAIK. I have come to the point where I have identied the wall that I wish to bang my head against repeatedly.

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