![]() ![]() In fact, W'bal went negative at the end of my TT. Nonetheless, you can see my W'bal plummet because 250w is definitely above my FTP or CP of 220w. I should have done this TT fresh, if I wanted a personal best time, but I had just ridden 8 miles prior. You can see I started out a little hot, close to 300w, and backed it down to about 250w. The segment of my ride highlighted in red is a 3 mile Time Trial on my Mountain Bike on the Tow Path. ![]() I suppose it's based on my FTP of 220 that I entered into Golden Cheetah. Not sure why Golden Cheetah gave me a W'bal of 20 kJ to start with. Here's a stress graph (from Golden Cheetah) showing W' for my latest ride today: How negative a value you can have for W' varies too. How long you can keep up the power at W' varies. The units for W', or sometimes labeled W'bal, (balance) is in kiloJoules (kJ). ![]() The value of W' where you start to crash and burn is around zero (0). Sooner or later though, whether you go hard or easy above your CP you're going to bonk/crash/run out of gas. How much it replenishes depends on many things such as the amount of time you recover, the power you recover to, etc. If you get a chance to recover during your ride, or take a break, it will replenish the W'. Go easy above your CP (say 250w in the graph above) and you'll last longer than if you went hard (say 300w in the graph above). Go hard above your CP and you're not going to last long. How quickly that fixed amount lasts is dependent on how hard you go above your CP and if you get any rest or breaks. If you're a math geek, and you want to calculate the actual W' value, all you have to do is find the equation of the CP line and integrate (using calculus). Now, the amount of work that you can do above your CP, shown by the red hatched lines above, is your W'. Want an easier way to compute your CP? Download Golden Cheetah software and use their CP and W' Estimator. You'll need a curve fitting software program to properly plot the graph and find your CP. Your CP, in watts, is where the line levels off. Plot the power (3 pts.) versus duration (time). Or, do a 3 minute, 8 minute and 14 minute Time Trial which I heard is a little better for plotting. To find your CP do a 3 minute, 5 minute and 10 minute Time Trial with a Power Meter. Critical Power (CP) is synonymous with FTP. Then, take 95% of that value and that's your FTP. Another way of determining your FTP is to do a 20 minute TT and find your maximum sustained average power. It's your average sustained power during a 40k TT. That is, it's your maximum sustained average power output in 1 hour in watts. Before I tell you what W' is all about, you first must understand what CP (Critical Power) and what FTP (Functional Threshold Power) are. I think it's a really neat/cool metric that wasn't and probably still isn't available in Training Peaks Software WKO+ 4. But if you do bike races or do hard interval training, it appears to me that real time access to it could be a game changer.Since I'm using Golden Cheetah software more often these days, I came across a metric called W prime, written W'. You can learn something from it.īut at least from my limited knowledge, it would be of little use if you are not going over your threshold since it appears not to start dropping until you get over your FTP. I do look at hard over threshold interval sets or races after the fact to see if I really did bury myself or, (more often unfortunately) I got to my mental limit before I really got to my physical limit. But after workout/race analysis is helpful tool. Basically, it would show you if you really had maxed yourself out or you are just being a wimp. If one had real time access to it, it would be a great training tool. Down to within 30-60 seconds in many cases. It seems, at least for me, to be an extremely accurate measure of when I am going to crack during hard efforts or repeated hard efforts. I've been using Golden Cheetah for about 6 months and I have to say W' is one of the most intriguing data points. ![]()
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