My question was following up on the fact that substrate utilization is influenced by diet. I wasn’t talking about exercise.
I amended the question for clarity.
So training the body to use fat by manipulating diet? You could probably increase fat oxidation by doing that (for that specific ride/period). Whether that improves performance (long term) is another thing. But would you not rather fuel to increase performance rather than to manipulate substrate oxidation?
I see them as 2 sides of the same coin. Specially useful for ultra stuff. Fueling has more logistical considerations. I could be misguided, but I was thinking along the lines of equal performance with less carb consumption via more fat usage. I see that as a win.
I don’t know why there is so much discussion on this matter.
Put the hammer down in 2 sessions, the rest ride as much as possible in low intensity.
This wouldn’t burn anyone out, makes cycling enjoyable as the rider has more “coffee rides”, and it is sustainable.
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The issue is that this is quite vague and subjective
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Or maybe it’s just an overcomplication of something not that complicated.
Forget power, just ride with your feelings. Can you do 3 3 hours rides in a row without being excessively tired? That’d be your zone2, low intensity, 60%, bang zone or if you want to call X zone, it’s up to you.
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- Re. your first question, go look up Louise Burke’s work. The answer, though, is that it doesn’t work - that is, you do burn what you eat, but performance depends on carbohydrate intake.
ETA a few studies:
(Note that Louise has been studying this question for a very long time, so these are just her latest. Also note that this is the sort of research that couldn’t be done here in the US, as there is no funding for it.)
- The iLevels are a. narrower, b. individualized, and c. only at higher intensities, where training is routinely performed in strictly structured manner. As such, the new iLevels (at the upper end, where things are different) would be more appropriate for prescriptive use.
With that said, take note of this at the bottom of the article:
“WKO4 Product Manager Tim Cusick contributed to this article”
As should be obvious from the change in tone, Tim actually wrote most of that article (as he was the one pushing for iLevels). I only contributed the first two sections.
- When chasing TT performance, I did all of my training at levels 2-4. But, I wouldn’t be necessarily recommend that to others.
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Might be out of my depth here, but wouldn’t it be more fruitful to shoot for increasing overall metabolic capacity (and eventually wattage and thus also fat use, even if substrate utilisation proportions stay fixed) via training than increasing proportional fat usage at a given wattage via diet manipulation (or secret sauce training), especially if the latter has the potential cost of overall performance decline?
This of course assumes that fat utilisation happens in mitochondria and that one can attain more of them - when you have more, you can burn more, etc.
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[quote=“buzzcock, post:1624, topic:43552”]
shoot for increasing overall metabolic capacity (and eventually wattage and thus also fat use, even if substrate utilisation proportions stay fixed) via training than increasing proportional fat usage at a given wattage via diet manipulation (or secret sauce training), especially if the latter has the potential cost of overall performance decline?
[/quote]
Train for performance and let the physiology figure itself out
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I wouldn’t say cadence is a actually major source of variability for substrate oxidation, I just like throwing around references that show that changing cadence changes everything 
This excerpt from the Rothschild et al modelling paper summarising previous research is helpful
In their model, they found that the combination of factors could explain between ~30-60% of the total variance, meaning that 40-70% of the variance is unexplained by all those “easily controllable” factors.
The Chrzanowski-Smith et al day-day reliability study was rigorously controlled in laboratory settings and still showed that level of variability between and within individuals.
So I would suggest that we cannot assume to have control of these variables in real-world training.
Again, this doesn’t make fatmax bad… this is no different from any other physiological or performance measure. Everything has uncertainty. How much does our FTP change on any given day? ± 10 W? 20W? What about at the start vs the end of the session?
I would suggest that being aware of, and accounting for uncertainty can allow us to be more confident in how we interpret change/improvement, and how we prescribe our training. Taking repeated observations over time helps to narrow down these uncertainties and increase our confidence - this is what coaching is: taking repeated measurements over time and using the overall trends to inform future training decisions & prescription. If I know nothing about an athlete I don’t know if a 5% change between any two sessions is normal, small, or big change? The more measures I take, the more can I understand how that athlete response day to day, then maybe I know that 5% is random noise in one athlete, and a huge meaningful improvement in another.
If I know my FatMax, or LT1, or FTP, etc. can vary by say ± 5% any given day, if I want to be training below that number, I’m going to aim for 10-15% below that number… That’s where I can be strongly confident I’m at my intended intensity. There is not much difference being 5 or 10% higher or lower within an intended training zone / intensity domain, but there might be more of a difference being 5% above or below into an unintended zone/domain.
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Re. the bolded part: if I get hammered the night before an exam and do poorly, is it because my native intelligence had actually dropped, or just that I couldn’t express it?
But, in terms of day-to-day reproducibility of FTP (or any other performance measurement), I would guesstimate +/- 2% if you standardize things as if it were a research study, +/- 5% if you’re just winging it/are a poor experimentalist.
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Yeah that’s the question isn’t it! The answer is probably “yes, and”.
There is pretty solid research pointing to physiological responses tend to be lower with prolonged fatigue. This recent one has some interesting findings, with CP not reduced after 90-km outdoor ride, but incremental ramp measures of intensity domains reduced.
Can also see blunted responses, e.g. if I’ve fatigued my capability to perform contractile work, I won’t be driving as high metabolic demand through peripheral structures. I won’t be able to express as high a metabolic rate, because another part of the system is limited.
The follow up question is, how does the adaptive signalling change under these different fatigue conditions? I’m really not confident in my adaptive signalling understanding. Assuming “yes, and”, that it all matters for different parts of the system, I can imagine certain signalling processes are driven more by external workload, and others more by internal metabolic load/stress?
How would you answer the question Dr. @The_Cog? e.g. if the session intent is to work above FTP but I can’t reach the target intensity for the target duration by the end with fatigue, do I prioritise meeting the intensity for shorter duration? Or vice-versa meet the duration at lower intensity? Or call it a day? (or just HTFU? 
)
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That seems about right at a cursory glance. This one found ± 15 W 95% limits of agreement test-retest FTP
This one found CV 2-4% in 20-min TT power output (part of an FTP protocol) between trials, but suggested the variability was too large to be used in well-trained & professional athletes 
Probably other investigations to consider.
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I don’t think you understand what I meant by “native intelligence”. By that I meant the concept of one’s inherent abilities, i.e., what an IQ test attempts to measure. So, I would answer the question as, no, your FTP doesn’t decrease during a prolonged exercise task.
As for the study you linked, #sportsscienceatitsfinest. That is, is it really necessary to do a study to know that fatigue occurs during exercise??
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Another waste of effort. The variability of laboratory-based TT performance is well-established and has been so for decades; there’s really nothing to be gained by focusing specifically on 20 min.
Same comment goes for studies looking at the correlation between 95% of 20 min power (i.e., Hunter’s estimate of FTP) and various definitions of lactate threshold. It’s been known since ca. 1980 that the latter is highly correlated with performance, and obviously multiplying one variable by a constant doesn’t change that fact. So, why bother?
As I tell my students:
Ask good questions, attack with rigor.
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Thanks again for the links. I was thinking something a lot less agressive than a Ketogenic diet though.
Could you elaborate on the sessions?. How do you prescribe Tempo or zone3?
“Aggressive” or not, as I said, we burn what we eat (over time, there is no other option), so higher fat intake = higher fat oxidation during exercise, but poorer performance.
Typical week:
M: 1.5 h easy (small ring only)
T am: 2 h w/ intervals (e.g., 2 x 10 mi TT, which ultimately evolved into the well-known 2 x 20 min erg intervals)
T pm: 1.5 h w/ intervals
W am: 2 h TAN* ride
W pm: training race
Tr am: 2 h w/ intervals
Tr pm: 1.5 h w/ intervals
F: 1.5 h easy (small ring only)
Sa and Su: group ride, longer solo ride, or race
*TAN = “tough as nails”, my answer/tip of the hat to LSD. I would ride the same 45-50 mi route with only one rule, which was that I had to be back in under 2 h. So, sometimes that meant just being a steady Eddy, whereas other times I might start out slowly but later have to really hammer to make up for it.
This was ~40 y ago, so no power meter, HR monitor, or even electric speedometer. Just a wrist watch and endless farm roads laid out on a one mile grid.
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It’s his own fault for renaming “zone 2”. He should have just said ‘train around 2mmol of lactate’ or at fatmax and kept the traditional zone names.
Plus he’s never, AFAICT, laid out a basic training plan or yearly periodization for the 6-8 hour rider that follows him on social media. Isn’t that what people here want to hear from him?
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Ah, apologies. Are you getting at something like, the construct - the underlying true property - of maximal metabolic steady state doesn’t change with fatigue, just the capability to express it or reach the same performance output decreases?
i.e. the operational FTP test to estimate the underlying construct of max metabolic steady state (or whatever terminology we want to use) will show reductions due to capability, not structural capacity? Or another example might be familiarisation to pacing a TT will tend to increase performance but not necessarily due to any change in underlying “fitness”?
What I was trying to get at is, at least some measurable physiological responses seem to change with prolonged fatigue. If (some of) my physiological responses are no longer steady-state at the same workload with fatigue, how would you interpret that?
Please describe more what you’re getting at if I’m still not understanding.
I don’t have your experience in this area. Could you share some examples that you think are well designed studies showing the reliability of FTP?