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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.
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!
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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