Current AWC (W') usage as data field on head unit?

Is there a cycling head unit that can show the current W’ reserve in real time as a data field?

Here is that data for me from a recent race effort which included a breakaway and then a final sprint. The first time it dips to zero is on the effort to break away from the field (over the top if a climb, hence why it bounces back as we recover on the ensuing descent), and the second time it dips to zero is in the final sprint. I’m somewhat amazed at the accuracy with which it bounces off the zero line!

It would be useful (feels like cheating, almost) if I had this available in real time. For example, some of the AWC reserve got spent earlier than it needed to, but at the time it felt like a negligible effort. So I think having this data available in real time would be very useful. Is there a head unit that does this? I don’t think Garmin Edge units can do it.

Had that in 2017 on my Garmin 520… not a chart but as a field (Xert MPA or something).


thanks, looks promising, I’ll give it a try. Does it require a subscription after 30 days?

I dunno, haven’t used it in years. I’d bet there is a W’ field on the Garmin app/widget store.

some things I’ve learned over the years:

  • its really really hard to go all-out over several durations, in order to get an accurate CP/FTP and W’
  • W’ going to zero is accurate, but don’t trust recovery time (there isn’t a good model for recovery time)
  • for those reasons, in real-time outside on the bike, I sometimes exceed Xert’s W’
  • and outside on the rivet, in a group, I found it very difficult to make decisions after a quick glance down at Xert’s MPA

Nowadays I primarily use W’ to come up with better pacing for all-out efforts (KOM attempts, or anaerobic capacity workouts).


Yes, you need to have an active subscription to use their Garmin widgets. Or at least you did in the past.

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Man, I can be a slave to my Garmin numbers at times while racing, but I don’t think I’d want to see that.

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If there was a way to show W’ on the screen it would be interesting to do a study on the accuracy. Then behind the scenes the researcher changes everyone’s values to 110% of actual, then proceed to see just how deep a person can dig when they ‘know’ they still have reserves.

What is accuracy in this context?

W’ is derived from a mathematical model and is calculated from actual performance data. Depending on the quality of the data one can claim with certain accuracy (usually 95%), that cp and W’ is within ± x units (watts and Joules respectively).

In order to obtain a good model with known accuracy, you will need at least three intervals to exhaustion over various length, usually between 3 to 15-20 minutes. The resulting model is then personal to you and your abilities at the time of execution, hence it’s a moving target.

My personal experience is similar to that of @WindWarrior: useful for pacing strategies doing KOM-hunting. Theory has lined up with reality within seconds on the short segments I have attempted.
I have no recent racing experience but I can imagine some usefulness in some cases.

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Yes, it’s a good way to calculate theoretical best efforts, but you don’t need a head unit data field for that. Personally I believe I have a pretty solid handle on CP and W’, and the graph for this particular effort bears that out. My use case is more about knowing when I’m fully recovered rather than knowing how much left I have to give, which I think I can tell by feel (as you can see, I finished both hard efforts at 0 joules remaining). It would seem I feel fully recovered at around 60% W’ reserve, as that’s when I start feeling like I have matches to burn. Of course, the deeper into a workout you get, the less helpful this field will be, since it doesn’t model fatigue.

It’s possible I should just be staring at some HR related field for this recovery status. Not sure which one though, because absolute HR varies a lot based on weather.

Have you considered Garmin’s “Stamina” or “Potential” metrics?


no, but that looks interesting — too bad I don’t currently have a head unit that supports it. Does anyone have positive experiences with this chart/field?

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AFAIK there is no good model for recovery rate, so treat that as a guesstimate. The burn rate is accurate with good data to feed the model.

Have you looked at Xert yet? I just pulled up a couple pages and there is some good info about MPA and how to use it in races or training.

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Yes, thanks for the tip. I started the process of signing up and sucking my data into xert (woohoo one more third party of questionable reliability who knows everything about me). I haven’t tested it out yet and don’t think I’ll be paying a monthly sub for this one feature.

The answer to my original question seems to be “yes, Garmin has it but is using it to incentivize upgrading to the newest devices (and they renamed it somewhat to make it seem magical)”.

I developed a Data Field for most Edge computers that shows both Power and W’ Balance in real time:

To ensure it is displaying accurate values for W’ Balance, it requires that you have solid grasp of your Critical Power and W’ values. There are many resources available to help with that.

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I haven’t tested it extensively, but I’ve generally found that it’s pretty useful. So did @dcrainmaker (go to the power guide section): Garmin Edge 1040 (with Solar) In-Depth Review | DC Rainmaker

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Have you looked at Garmin apps? There has to be a data field for W’ from a developer.

I’ve got an 840 and wanted to upgrade for other reasons. Since its based on FirstBeat, if you do upgrade then the requirements to make use of Stamina are:

  • feed it enough data for it to estimate your vo2max
  • make sure HRmax is set correctly
  • make sure your Activity Class is set correctly

Thank you!! Installed. Just released a week ago, what brilliant timing.

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Thanks. I will be sure to get around to trying this whenever I upgrade my edge but this isn’t the must-have feature that climbpro promised to be.

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FWIW I upgraded for the touchscreen as nearly all my training is outside. ClimbPro is nice to have, but not my reason for upgrading.

I’ve had a couple chances to try this out now and I give the app a 5/5.

I watched the field in a practice crit, and it didn’t end up being particularly useful because tactics dictated the way I “raced”. But I was at least able to verify that my perceptions and the number on the screen were pretty closely matched, and I got a visual representation of exactly what percent of my matchbook it took to open a gap vs sustain it. It’s probably more useful for less experienced riders (I’ve been racing for 15 years) but I think it can be useful for anyone. In particular when you’re at or near 0% it may feel like you’re still going hard, but in reality the numbers don’t live up to that perception. You could stare at your 30s power to figure that out, but that has a 30s delay.

It was more useful in a rolling time trial (well, solo effort for no particular reason, but let’s call it a time trial). Hitting a 5’ climb halfway through the effort, I was able to look down at my W’ balance and see that I was already down to 50%, then I could try to keep it steadily dropping on the way up the climb (instead of blowing my load halfway up it). I know this course pretty well so I don’t think I was likely to blow anyway, but it’s still a nice way to anchor the effort when adrenaline/caffeine are drowning out the normal pain signals :laughing:

As far as execution, it fit into my data screens flawlessly because I already had a large field for 3s power, and this takes just a small slice off the side of that one. Plus the color coding makes it a lot easier to interpret at a glance.

Highly recommend!

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