In podcast #189 Chad discusses fractional utilization to try and help to determine whether you should focus more on VO2 intervals versus FTP intervals. I found it a little confusing. Can anyone give me an idiots guide to this
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Hey @WEK, I’m definitely not an expert on fractional utilization, but I sent your request over to our coaching staff and will report back if I hear anything from them!
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(Someone correct me here if I’m wrong but I think I have this correct).
Your fractional utilization is the relationship between FTP and VO2Max (FTP/pVO2 = fractional utilization)
If your FTP is 200w and your sustainable power at VO2Max is 240w, your fractional utilization is 83.3%.
In some cases, people push their FTP to a high fraction of VO2 (between 85-90%). This represents an opportunity to improve VO2 max (or in someone like Froome’s case, a rare genetic gift of efficiency).
Conversely, you can have a low fractional utilization (below 75%) which means that focusing on FTP is likely going to benefit you more, to being up closer to the normal range which is 75-85%.
IMO, a simple way to determine this is to look at the average power you can do 3-5 minute repeats at and compare it to your FTP. If you can do 6x3min repeats at 280w but your FTP is 200w, you would prob benefit from threshold workouts since your fractional utilization is low (200/280= .714 = 71.4%)
If your sustainable for VO2 work is more like 220w at a 200w FTP, you should probably focus on VO2 work instead, since you have a high fractional utilization (200/220w = .9 = 90%)
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What @stevemz wrote…
More accurately the title might read “Fractional Utilization of VO2max”. Or the % of your VO2max where LT/FTP happens. So yeah untrained athletes may see LT/FTP as 50-60% VO2max whereas trained athletes may see it at 75-90% VO2max.
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I am unfamiliar with the topic, but edited the thread title as suggested.
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Oh you 80/20ers! 
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Lol, that’s not the reason… silly nut.
Put another way (if I’m interpreting you right)… if you’re unable to complete VO2 max workouts at 100% intensity, you should consider focusing on improving your VO2 max. If you find VO2 max workouts easy, consider focusing more on threshold workouts (or other workouts to raise your FTP/endurance).
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That would be me. I’m well aware of the sucky nature of my endurance/threshold.
That said, VO2 work will raise FTP…damn you body for not being black and white! 
That’s one way of thinking about it, but there is more going on in those VO2 workouts that make it a bit less straight forward.
I’d say if you are significantly outside the normal range (75-85% for trained athletes) in either direction, it’s worth tweaking your training accordingly by selecting an appropriate plan if it matches with your goals.
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I think the responses so far are on the right track, but I did have the following thought when listening to the discussion on the podcast:
Most people are using a proxy test for their FTP, be it the ramp test, 8min test, or 20min test. I find I get different results between the tests (although I haven’t done a 20min test for a long time), and to some extent I would expect the shorter duration tests might be more representative of max aerobic strength than hour strength. So if you’re trying to look at your fractional utilization to decide where your training should focus, would it not be better to calculate the ratio based on FTP derived from a longer (say the 20min) tests?
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In my personal experience yes or you can look at your power curve if you are confident you have gone full gas for different durations. Otherwise you are using a test that expects you have an average power curve.
I have a strong vo2 max and so get a much higher ftp if I do the 8 minute test, compared to 20 minute, maybe as much as 30 watts, ramp test gives me somewhere in the middle of the two. I did an hour at full effort as a test to check too because if I was going to make changes to my training I wanted to be sure. Fortunately the 20 minute test and hour give same result for me as long as I do a full effort for the 5 minutes prior to exhaust my vo2 advantage.
Fractional utilization of VO2max is nice to know and I look at it as one of many markers of fitness. But, it doesn’t change the methodology of training. The whole point is to move the line to the right. I can’t recall where I read it but, a well known coach said something like “training to increase FTP will invariably increase everything else along with it”. Meaning if you move your FTP say from 75% to 85% of VO2max I would your VO2max (power) and all other metrics will probably increase as well.
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Bump.
After having completed SSBHV2 – which is 100% Sweet Spot – I did the ramp test and my FTP dropped 2%.
A bit disgruntled with that result yesterday, but today I think I’m more than ok with that result. Smart people correct my thinking if it’s not factual, but just from doing a couple outside rides, I would say all the SS work has increased my fractional utilization* even though i) the ramp test doesn’t display that, and ii) my VO2 ceiling has dropped due to lack of high end work.
For others who experience this, I propose two courses of action:
- up FTP to a reasonable level whilst lowering the intensity of VO2 workouts (if necessary). After a couple of weeks of raising the ceiling things should be back in line (better for Threshold work);
- go with the ramp derived FTP for all subsequent workouts and, as above, after a couple weeks of VO2 work the ceiling will be back to pre-SSB levels…but now with a higher utilization (better for VO2 work).
In either case, the next ramp test should see much more FTP improvement.
Although I’m training for a steady state race so maybe I just suck it up and live with a lower ceiling and higher utilization.
Time for more coffee. 
*(a quick scan of FUoVO2max research shows that weight lifting increases FU, in part due to increase in quad size and strength…which is basically what SSBHV does, just on the bike.)
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It might not be that simple, but I think there is something to it. I opted for Sustained Power Build because I was seeing strong gains in FTP without overemphasizing raising my ceiling (VO2 max) meaning I am focusing on filling the cup up first, then I’ll go back and work on making the cup bigger next Build.
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Sounds plausible. That’s a limitation of relying on one test like the ramp test - can’t independently determine VO2 and FU.
Ideally, would do a 5 min max test to determine VO2max. And maybe something like the 20 min test to determine FTP. From there, you’d know both VO2max power, and FU.
You’d need a longer test than the 20 minute test to remove the effects of anaerobic contribution, even with the 5 minute effort ahead of time.
Ramp Test + a 35-50 minute test works great for me. Best of both worlds.
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It might, but i think i heard Chad saying that weights, and the additional muscle created, would be better at shuttling the byproducts of aerobic exercise away. And this extra muscle doesn’t need to be on the legs.
Additionally, re leg mass - it could be argued that to gain the same adaptation on the bike as weight training you’d probably need to be doing hard anaerobic intervals.
What do you take from the ramp test as power at VO2max?
Agree - longer than 20 mins better for FTP, it’s just harder 
.
Even though, a single 35-50 min test is easier than the multiple ~30 min tests in traditional MLSS testing!
Any chance you can review your Personal Records, via Seasons and Season Match, to see how you are doing no compared to other seasons?
Specifically, looking at power in the longer duration areas or simple Time to Exhaustion realm.
FTP is what it is, and a steady or dropped one is only one indicator. You may well have improved in other ares. I am guessing that the FUVO2 is one other way to look at the bigger picture, but the PR or other tests mentioned may help see where you are.