Hi,
I’m curious to understand why the W’balance is going down while doing an interval with a target Power below CP:
In the case above you can see that the interval target is 260W, and my CP is 263W. Why the W’ balance goes down there?
I knew that we use the W’ “fuel” only when the current power is above CP. Basically (Current_Power - CP) * duration_in_seconds is the amount of Joules used from the W’balance (when Current_Power > CP)
Thank you!
Seems there is a bug, it is using your FTP as your CP… We will get this fixed.
Yes, I thought the same, that it uses FTP instead of CP
ps it’s OT, but in the CP and W’ calculator I would add the model based on 3 points, that seems to be more accurate. People can eventually leave one empty, and you’ll use the current model based on 2 points
There are two sides to this problem. Their is the CP, W’ calculation and then there is the W’bal calculation. The problem is the W’bal method we are using only takes 2 parameters so this ends up making the two methods work very inversely similar.
None of this stuff is exact science… it’s just a ballpark that is much closer than using FTP only. Also realize that many people are taking these values from different days so again it’s very ball park. It’s just interesting that even with these ball park figures it can end up very close. But even the definitions of FTP and CP are very fuzzy… Now come on is it 20,40 or 60 minutes… Both of them are based on a power you can sustain for a long time and no one can even sustain their CP or FTP for 60 minutes 
W’bal is obvious math, right? (power-CP)*seconds
CP, W’ are based on models and you’ll have more/less screwed figures based on the model and on your individuality (if you’re a super strong sprinter or a super strong time trialist the model probably will not work perfectly - and in opposite directions)
In theory CP is the effort you can sustain over 30/40 minutes, while FTP on 60 minutes - and this is the reason that CP is normally a little bit above FTP.
This is at least what I’ve understood so far
That’s all an over simplification Again trying to map math to physiology is always a rough estimate. There are always tons of exceptions to everything. Focusing on the basics is enough. You don’t need perfect because you always have to add your own modifications especially if you want to go to 100% failure (which we don’t advocate, but if you believe that is best for you go for it ).
I think the most important reason for any of us to use CP W’ for this is to understand how these energy systems work, and seeing that the math basically works helps confirm this. It also gets you in the ball park for designing workouts that will completely exhaust you at the right or maximum level but it’s always still going to just get you in the ball park no matter how perfect the math is.
The way coach jack works in it’s progressive nature you will learn your limits. Now CJ VO2max or HIIT is actually different intensities for different people with different rider signatures… So some work harder and some less hard but overall since we don’t try to take people to the end of their limit it’s not so critical. They also can just slide the starting slider harder if they chose and the rest will fall into place.
I agree @Alex
I’was just suggesting the approach of Golden Cheetah - we all know that averages lie on average 
Yes, our goal here is to keep it simple and give the most basic options when possible… So very small incremental and questionable value is limited… I do not want to be like Golden Cheetah or IntervalsICU…
