W’bal is perhaps less important to triathletes than other cyclists but here you are reading about it; so let’s go and find out why W’bal might start to appear on your Wahoo ELEMNT or Garmin Edge 820 in 2016/7.
First off, W’ is pronounced “double-you-prime”.
W’ bal (balance) can be seen as the amount of oomph left in your body. See it as your reserve of ANAEROBIC Watts
W’bal also known as the Anaerobic Work Capacity – ie how much anaerobic work your body is able to put in at any given time during the ride.
You obviously CAN crank out higher watts than your FTP at any given time over a 60 minute CP60/FTP test but when you do that you are eating into your finite stores of W’; and there is always a payback.
Similarly when you slack off slightly you replenish your W’ stores and you will likely replenish them at your own rate (your ‘tau’). W’bal is the balance for you of “how much W’ you have left”.
As I said, in layman’s terms, it’s how much ‘oomph’ is left right now.
When you’re road bike racing, a W’bal metric is a good thing to know (well it would be if you had it on your cycling computer). It’s less good to know in a triathlon race where you almost always want to maintain a constant optimum power output below FTP (draft-legal changes this to a degree) but W’ is of obvious use for ‘proper’ cycle races eg for hills or sprints where race tactics dictate going above your FTP from time-to-time.
I suppose, too, that if your training plan specified some form of interval repeat to ‘exhaustion’ then W’bal is an OK way to see if you really have done it to exhaustion. Of course you might not like your coach to have stats that show that you are an occasional slacker 😉
Taking the above example from a Golden Cheetah analysis, I think it is a set of 5 minute intervals executed at something like FTP. W’bal is only going down to 15 whereas this athlete often gets down to well below 10.0. The yellow is the pure WATTS. The Red line is the W’bal. So this looks like a perfectly executed session then with consistent efforts and similarly depleted levels of W’bal?? No, probably not. The session looks too easy for the athlete. Either she didn’t hit the specified watts or the specified watts were too low (maybe an out-of-date FTP?).
Imagine you are a coach and you’ve asked your newest athlete to go flat out for 30 minutes (CP30 test). The athlete is new to training with power and has already noted her concern to you that her left:right power balance seems ‘out’. What do her test results show? (again the chart is from the free and awesome Golden Cheetah software)
The (manual) dotted, yellow horizontal line shows the FTP derived after the test.
Starting off with the power balance.
The mid-screen up and down red bars represent %L|R power balance.
So the power balance is quite strange. At low wattages the athlete’s power balance is quite right-focussed (before and after the test). Yet during the test it looks fine. There probably is something ‘wrong’ with her technique that she needs to work on but I would not be as overly concerned as she was as, once she gets cracking, the problem seems to go away.
Anyway, back to the CP30 and W’bal
This was the first time she had ever done a CP30 test, although she did have a few weeks of experience using a power meter prior to the test. In terms of pacing the test as a first-timer, I reckon she did a brilliant job. It’s a pretty consistent effort. There was clearly more effort at the end, pushing the watts higher but at that point the W’bal starts to fall quite quickly. So although her effort was NOT an optimal 30 minute effort it wasn’t too far off. Aim to average 5/10w higher next time and she’d be close. But this is a usable test to work out training zones IMO. I’d favour the scientific approach of adding on 5w to the FTP as that seems ‘about right’ 😉
Wahoo, Polar and Wahoo
I don’t recall ever seeing this on a cycling computer (Edit: see below…they NOW exist). IMO it is surely useful. Actually very useful. From what I’ve read some of the computation stuff is a bit CPU-heavy. That may make implementation on a cycling computer too tricky as it will have to simultaneously cope with: the SMS status of your phone; polling for ANT+ sensors; and lots of other relatively useless stuff. Although it would only need to be activated once your power exceeds FTP.
So, if you train with power, would you rather have this or another power-derived measurement of whether you are sitting or standing?
Well. I thought it was interesting 🙂
PS: It may well be possible that there is PC/MAC-based software that can display this for indoor sessions. A live session in Golden Cheetah may well do that. I will have to dig further (or let me know). Thank you!
See Connect-IQ (v1.0): https://apps.garmin.com/en-US/apps/6dcfffe5-cd3d-41f3-8ba3-13fa0647b003
Also See Connect-IQ (beta V0.4): https://apps.garmin.com/en-US/apps/fbf7b796-40b2-4e57-9bc1-c8937a131b71
Edit: Dec2016: Also have a close look at some of the newish CIQ apps from XERT. clever stuff along these lines. In fact Xert’s MPA is effectively W’.
Sources: loads of stuff like this on goldencheetah.org and the maths/stats/science goes back originally to the ’60s; Connect-IQ; Fabrice and Gabriel – thanks all.