Garmin Stamina – An Explainer
Garmin’s new Fenix 7, Epix 2, Forerunner 955 and Edge 1040 have an intriguing new metric called Stamina that you can see live on your watch or on your post-workout chart in the Garmin Connect app. We all intuitively know what Stamina is yet no one seems quite able to explain this new metric in the Garmin context. So let me have a go here! I think what I’m saying here is about right for a simplified explanation and would welcome clarification in the comments.
Must Read: Garmin Fenix 7 Review
Q: What is Garmin’s new Stamina metric?
A: It’s very similar to W’ Balance (pronounced double-ewe-prime Balance)
Q: What’s W’ Balance?
A: It’s sometimes called Anaerobic Work Capacity (AWC)
Q: What’s AWC?
A: It’s very similar to the inverse of Xert’s MPA or to a cyclist’s match book
and so it goes on…sorry, I’m teasing! 😉 I’m just making the point that this all is nothing new.
Wikipedia says that stamina and endurance are the same.
In a nutshell, Garmin’s Stamina is how much oomph you have left in your tank.
Some Examples, by way of explanations
You might have a constant steady speed or pace that you can maintain for hours but at some point, you will stop. This chart shows me running for about 90 minutes with a straight line STAMINA declining progressively throughout which would probably hit zero after two and a half hours.
There are some incorrect HR peaks at the start but then I settle into Z1 until about 50:00 when I increase the pace to my aerobic threshold Z2/Z3. That’s an entirely fat burning effort to this point and if the straight line continued declining at the same rate it would have me stopping after about 2 and a half hours. I reckon it would be 3 hours in reality but it seems about right based on how I felt that day.
Contrast that to the following chart from a different kind of bike ride. I was cycling with a couple of other people in a half-hearted attempt at a chain gang. We were going slow, then picking up the effort for short sprints, losing a slow rider, almost stopping and it wasn’t especially tiring. You can see the gradient of this stamina line is shallower than before. That reflects the differences in the X-axis scale(!) and the fact that I could have easily gone at this pace, or steadier, for several hours more. ie You can cycle aerobically for longer than you can run aerobically, or, at least I can!
You can also see where I’ve circled two deviations where I targetted two Strava segments and the wind was blowing in the right direction! I was starting to burn some serious carbs for a few minutes. Intuitively it must be right that if you interrupt a steady-state effort with an effort increase then your eventual exhaustion point is brought closer in time. You might also speculate that a much harder, more sustained anaerobic effort could bring you to a standstill even quicker, say in 10 minutes or less.
Like this…
Here’s another more marked example on a Wahoo Kickr Core. From 25:00 to 35:00 I get to my Z2/Z3 boundary and I’m still going aerobically. But then I markedly increase my effort to around FTP. As you can see this eats rapidly into my “actual” real-time stamina. I recover and then have another crack at 55:00 by which point I’m tired. The end result of only about 20 minutes of hard effort in a 50-minute workout is that my actual stamina level is down to around 25%. If I kept trying that hard then I wouldn’t have lasted much longer. Yet, if I eased off, my carb stores would recover and I imagine that the Actual stamina line would recover upwards to the potential stamina line and then I could keep plodding on for several more hours. Note that my anaerobic effort permanently lowered potential stamina.
I mentioned W’ Balance Earlier
I think it’s starting to make sense now. It reminds me of W’ Bal, which I use as a power-based metric in Golden Cheetah and which represents my remaining anaerobic energy levels. It’s the red line in the following chart from a ride where I was doing some ‘quite hard’ road bike hill reps. These were all anaerobic reps and you can see that I quickly ate into my anaerobic reserves which are subsequently replenished back up close to the red 20Kj level as I cruise down the next hill for the next rep.
Thus W’ Bal reflects my anaerobic energy reserves. It is the energy in my tank BUT just the anaerobic energy. I have aerobic energy too, of course.
So, now if we look at the exact same ride in Garmin Connect we see a similar but subtly different chart, like this…
The difference here is that Garmin’s Potential Stamina line equates to Golden Cheetah’s 20Kj line. BUT the Garmin potential stamina line is also trending downwards as my muscular and aerobic abilities decline somewhat independently of the effect of the anaerobic hill reps.
If you look again at how close the yellow line recovers to the Potential Stamina line it’s pretty similar to what I showed further above on the Golden Cheetah chart where the red line doesn’t quite recover to 20Kj.
Thus I’d be extremely surprised if what Garmin has produced here is not closely related to W’Bal with a twist for the aerobic decline.
How is this calculated?
Check out this on GitHub if you fancy implementing something similar yourself.
The essential calculation must be based on either your time in each heart rate zone or power zone but with a lot of fancy bits added on that 99% of us will never understand, nor want to understand.
I don’t think anyone quite knows the exact calculations and full data sets that Garmin use.
Where is it stored? Is it stored?
Both actual and potential stamina are stored as new fields in the FIT File and so any other sports data platform can use the Stamina info if it wants to.
What Are The Uses?
It’s a useful metric. Its uses range from assessing how easily/how fast you can complete the race/workout to checking your post-workout stats to see if you really did go flat out in the hard bits.
You could even use the Stamina level as a target in intervals. Let’s say you target reducing stamina to 20% in each interval, well, what it takes to get to that point varies by how quickly and how hard you build up to it plus it varies based on your previous intervals. Thus each 20% depletion interval could appear quite different from a watts or pace perspective but the end physiological goal MIGHT be the same for each one.
There is a lot more you can do with this type of non-traditional metric. Ask Xert…they’ve been doing it for several years already and I’ve been using their platform for years too!
More: Baron Biosys (Armando@ Xert Online)
More: Mark L from Golden Cheetah
Has Garmin Done A Good Job Here
Yes, it looks like it: Providing your HR data and zones are correct.
I initially thought this would be a useless gimmick but I’ve changed my opinion quite significantly after a couple of goes with it and looking at the data it produces.
In some ways what Garmin has done here makes more intuitive sense than W’ Bal by itself and certainly shows actionable information. Plus Golden Cheetah just lets you analyse completed workouts but my Garmin Fenix 7 will let me look at this in real-time.
Garmin being Garmin have flushed out the list of related metrics so we have all of these: Current Stamina, Potential Stamina, Distance Remaining, Time Remaining, Stamina Gauge (Distance) and Stamina Guage (Time). I particularly like the Time-based gauge which shows you how long you can continue for as well as your current Stamina level.
More: The information on the image below is an explanation of Stamina from Garmin. thank you for reading!
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That’s an interesting and thorough analysis, thanks. I wonder if it’s not more actionable for bike riding though, where you can actually recover or for running intervals, as opposed to steady pace races like 10Ks or HMs. I ran a full out 10k myself last Sunday (close to the time predicted by my Epix) and was told I still had 40% potential stamina at the end…I was exhausted ! There have been similar reports of an full out HM ending at 30% stamina. So yeah I suppose I could have kept going after a 10′ rest but that’s not exactly useful during a race. Maybe it works better for longer races like a marathon ?
hmm, yeah for 10k/5k it should be close to zero i would have thought
bike: yes recovery is recovery, it will just be at different rates. is that factored in? IDK
Yes, should be close to 0% regardless of the race distance but so far I haven’t seen any hint of that. It seems Stamina is more focused on Anaerobic efforts than Threshold efforts where you’ll be close to zero between 40 and 60 minutes…
yes
but you see the charts i include in the article.
regardless of anaerobic efforts the stamina declines
Very slowly though. Strangely it seems they are not factoring Threshold running in their calculations.
idk.
if you look at the Polar calcs for fat/carb usage then there is a marked changed at above that point. perhaps both reflect a significant change when going anaerobic.
Fwiw – I asked about 5KM and 10KM races, and they said that realistically it’s a crapshoot if it correctly nails a 5KM race, because the timeframe is so short. On a 10KM, they said it definitely should, assuming it’s got everything correctly configured.
In general, in my experience, it’s been pretty scary-accurate at long-term duration stuff (like 5-7+hrs), but a bit more wobbly for short-duration stuff (e.g. one hour of intervals). It also tends to struggle with non-intense activities (like hiking), though, it’s not enabled on the hiking activity profile. But if I use the trail run profile for a long hike, then it seems to underestimate my capacity/will.
For the primary use case of endurance training/racing though, I’m reasonably impressed with it. Do note that as outlined in the article, your recovery time is a big factor in these calculations (from previous workouts).
it sounds then like it is very sensitive to the correct determination of LTHR/LT2 (which can vary considerably from day-to-day) and sensitive to efforts above that level. And, of course, that precisely means sensitive to the W’ component that gives sharp declines.
concluding from that maybe it’s just the longterm Potential Stamina piece that’s accurate, perhaps garmin can simply estimate the slope of the declining line based on sport type, your fitness level and time in Z1/Z2.
Although if only ‘Potential’ Stamina is accurate then using the word ‘Potential’ doesn’t inspire much confidence.
My enthusiasm has now waned somewhat.
Yeah clearly they should be able to factor in Threshold running, especially since they have a LTHR value (correct in my case for HR, a bit too slow pace) so after one hour (at most) of running at LTHR, potential stamina should be equal to zero, that should be easy enough to add to the calculation.
Following up from your post I found the data pretty interesting having raced this weekend. Whilst I didn’t use the stamina meter during the race I looked at the stamina data post race this weekend. Didn’t use during the race. Pleased to report that it was very accurate and would have been helpful during the race. My time for context 47:07 – Stamina hit 0% at 46:36 at which point it’s just abut guts and determination to finish. I had 14% about a minute earlier, when I started my kick to the line. Appreciate it’s 1 race for 1 person but backs up to me what you shared in your post about it being useful for 10k plus. On the basis of this result I may consider using it in future for races from this distance upwards.
Good for you but that’s really odd given the multiple feedback for 10k and HM races where it ended at 30+%. Hard to imagine that you lost 14% of stamina in a minute !
Was it close to your predicted time ? Do you haven an LTHR value ?
As you have said Garmin are effectively modelling the depletion and recovery of your work capacity in a more accessible way (W’ balance, AWC, RWC, whatever you want to call it).
– Firstly I would expect this needs calibrating with max efforts at different durations to be truly accurate. (I did a CP test on the weekend using the stryd pod and was at 0% stamina about halfway through each of my 2 segments – 3:00 max and 10:00 max tests). By the end of a race if you’ve given it your all or close to the stamina meter should reflect that and be at zero, certainly under 5% no matter the distance or duration.
– Secondly I’d assume a minimum period of training data would be required to accurately assess stamina capability. 30-90 days most likely.
– If you are using a power meter already, and have a well calibrated power duration curve in your chosen software this is probably less accurate than that.
– However this seems like less work than using WKO / Golden Cheetah or some of the other platforms.
– And it’s also calculated in real time which is useful, and as far as I’m aware not possible in any other way right now.
It leads me to the question of whether Garmin will bother with running power especially and use this as an easier and simpler tool for the majority of runners who prefer pace and heart rate. Or is this the beginning of them using tools that help people make the leap to power.
yep I agree with all that
I’m not sure where Garmin is getting the historic calibration from for this. as you say it must be calculated to get Stamina right. And it could be more complex than power curves as it might also incorporate personalised recovery rates (or should do)
running power: my thoughts were that this kind of model would have been easier to develop with power than HR. I assumed they’d done that first for cycling then PERHAPS used whatever power models for running that Garmin already has behind the scenes.
does this help people leap to power. not sure. in some ways it’s a bit more complex than the beginner level of understanding power.
Seems like a step or two better than Performance Condition, but perhaps it is just a step different. The example on-device screenshots circulated so far feel a bit less glanceable than most. In any case I want to try it when it ends up on a Edge product.
It isn’t clear power curve tracking would be dependable unless they have been storing more than just record power and recent power data. Perhaps they can extrapolate expected best case power at low stamina as a percentage of best expected power at other stamina levels.
yes
you should look at xert, it does all of that.
if i just cycled i would exclusively use xert.
Is it possible to download the FIT file from either Garmin connect, or directly from the watch to a computer. I assume a FIT file is generated.
thanks
yes in both cases.
do you mean to ask if the stamina metric is in the fit file.? I have added an image in the main article showing what data is stored in the FIT file. The data is also stored in garmin connect and used on the charts there
In any case it is a bit scary to tell you that you have (i.e.) 80 Kms in the tank.
I am very very curious how could one deplete his/her stamina in a workout.
I’m not sure at what level you are asking that question.
one answer would be consuming all available carbs in muscles/liver.
another is to consider simply what stops you going any further/faster
I wonder how this metric coped with intake of energy gels etc. For instance, supposing a marathon runner ran low in glycogen by 20 miles and was unable to carry on further? How would Garmin know whether he had taken more on board. Is it assumed that adequate calories are being consumed to avoid running out of energy? I suppose my confusion is the meaning of stamina. The leg muscles could be fatigued without having run out of fuel.
well….
precisely.
Until they have a blood glucose sensor involved they likely have to assume that event intake is similar to training intake. There are certainly reasons in an event why that may not be the case, but then the user will reasonably notice and adjust their interpretation.
I suspect like Performance Condition it has most actionable value when it gives the user a number that is wildly different from what they anticipated while still being an accurate. Numbers near expectation ought to provoke no particular change. An especially poor number flags for the user they need to look for other indications to confirm their original plan is in jeopardy.
In the same way Performance Condition provides a bit better real-time assessment than Training Effect, the new measurements also increase the utility of the device just a little bit longer into efforts. The amount of data and computation for the incremental improvements definitely feels non-linear.
A few years ago there was an observational study that found evidence in US marathons there is a specific, moderate pace that is mathematically unlikely to be successful. Both runners targeting less and runners targeting more had statistically better chances of success at their pace target. The organization that found it in their post-run surveys wasn’t focused sports nutrition so they offered no explanation. Enthusiast opinion seemed to be it was the point at which under-fed runners paced too fast, and over-fed runners paced too slow.
Hi! I am really interested in your analysis in the Garmin stamina level. May I know your contact details, such as the email, so that we could discuss more?
in**@th*********.com
It seems pretty useless to me. It was down to 1% half way through my first 50 miler and I made the finish just fine with no second half slowdown.
i’ve bemoaned garmin’s algorithms quite a bit recently.
stamina seems to be not so bad for me.
explanation?…none!!!