What is your energy source when doing ftp or sweet spot. Like 80% aerobic 20% anaerobic? And can you get it to be more aerobic?
jeff
The answer: it depends. Listen to the most recent Fast Talk podcast to find out more… I’ve been slowly wading through research papers myself trying to figure it all out. The answer to this question will depend heavily on the trained state of your anaerobic system (your VLaMax). This is my understanding so far, but someone please correct me where I’m wrong:
If your anaerobic system is completely de-trained (not possible in practice), your threshold would be basically identical to your VO2 max, because there is no lactate being produced, which would mean that no acidic byproducts are fatiguing the muscle prior to reaching VO2 max. In this case, threshold is completely aerobic. However, this will ultimately limit your VO2 max because all the energy would be produced by converting fat to energy which is not very efficient by itself. Usually your aerobic system relies on fat and the lactate produced by your anaerobic system to produce energy.
On the flip side, if your anaerobic system is highly trained, then the acidic byproducts of glycolysis will prevent your muscles far before you achieve VO2 max, and effectively your threshold becomes much less aerobic.
Both systems are trainable, but they are coupled so it’s hard to change one at a time. It seems that the general protocol for optimizing FTP, for example, is to heavily train the aerobic system (raising VO2 max) and adjust your VLaMax order to optimize the percentage of VO2 max you can hold for 40-60 minutes. However, it seems that in general with this approach optimizing FTP is not the goal but rather optimizing power for the duration of the event. For any endurance event the FTP will probably be improved but it’s not the metric used to track progress.
This site has a bunch of info about these concepts: http://www.lactate.com/lactate_cycling.html
Edit: If there is a bunch of misinformation in this post I’ll remove it, please let me know. I’m just trying to learn how my body works 
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@ madman
great response.
3 energy systems: ATP-Pc and Glycolytic (anaerobic) and the oxidative (aerobic). From everything I’ve read we use all three systems all the time.
This is from memory and I’m basically parroting what I heard explained in another podcast so check it out: glycolysis (produce lactate) is desirable for more sprinter types and therefore to be better at sprinting a rider should do specific gym and bike sprint training to mimic high yet shorter duration peak power outputs (10-30 seconds).
Time trial/climbers rely more on the oxidative/aerobic system (use lactate) and should focus more in the SST region.
So yes both are trainable. Any exercise physiologist out there chime right in! 
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My understanding from reading and listening to exercise physiology podcasts:
If you are riding below MLSS (maximum lactate steady state, which is close to FTP, but maybe a little less) - which let’s assume sweet spot is - then the maximum amount of energy that can come from anaerobic glycolysis is less than ~7%, with the remainder coming from aerobic breakdown of lactate, glycogen, and fat. Although, at intensities approaching MLSS, energy from fat oxidation (which does not produce lactate, and is fully aerobic) is likely quite low (relative to glycogen/glucose oxidation).
My reasoning behind this: anaerobic glycolysis of one glucose molecule produces 2 molecules of ATP (the energy source ultimately used by the muscle), whereas aerobic consumption of one glucose molecule produces 30+ molecules of ATP. At intensities under MLSS, for 2 ATPs produced by anaerobic means, ~30 ATPs are produced aerobicaly from the lactate which is a byproduct of anaerobic glycolysis. So 15 times as many ATPs from aerobic vs anaerobic means (1/15 = 7%).
Any additional ATPs from aerobic breakdown of glycogen/glucose, or fat would make this % lower.
If you are riding above MLSS, then this logic no longer holds, and a higher fraction of energy is produced from anaerobic sources.
Another related question is how much energy comes from glycogen/glucose vs fat. This is a very important question for long distance rides, as glycogen stores are limited, and only so many carbs can be consumed.
The best way to train to improve fat metabolism is to do long endurance rides. Shorter depleted endurance rides also work.
You can also change your diet, to reduce your carb consumption. It the extreme, this becomes the keto diet. This diet-based approach is usually what people are referring to when they say becoming “fat adapted”.
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@madman2 and @DaveWh already gave some great answers.
To add my two cents:
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The one thing I would disagree with from @madman2’s response is that it’s hard to change only one system at a time (aerobic or glycolytic). It can be done, but requires careful consideration of how to train and knowledge of your own physiology and metabolism.
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Although nutritional strategies can be used to alter the contribution of aerobic oxidative/glycolytic energy at any given power, the very large part of changes will come from the actual training done, not from the way you eat.
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From the testing I’ve done on myself and athletes I coach I’ve seen that typically around 92% of the energy at FTP (note - true FTP, I’m sorry but the ramp test does not give you this) is aerobic, 8% anaerobic. For an all out 4-minute effort, 80-85% of energy is aerobic.
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For the aerobic energy and how it breaks down into carb and fat oxidation, see the attached chart that compares two riders with fairly simliar VO2max. The solid line is a rider with a VO2max of 55 and VLamax of 0.5 (“all-rounder”) and the dashed line is a rider with a VO2max of 58 and VLamax of 0.3 (diesel engine).
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For clarity could you please post how you are defining “true FTP”?
As far as im aware there is no single agreed definition and all of the testing protocols available today (be it Ramp, 8, 20 or 60min tests merely provide a number, based on a theoretical concept, to base training on?
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Great example showing how carb vs fat can be different between athletes, despite similar VO2max (or FTP). For long distance/duration events like Leadville (which I’m riding this year), I’d prefer the profile of the diesel rider.
Curious - how do you measure the aerobic vs anaerobic contributions? My math above on the 7% is based on my understanding of the theory - but it’s just that, the theory, and not actual measurement.
Your 8% is obviously close to the 7%. One potential difference could be that the athletes riding at FTP in your tests are riding slightly above their MLSS (which I’ve read is often true for FTP vs. MLSS). And this could explain the slightly higher anaerobic contribution. But at this point we’re splitting hairs.
At this pace, the athlete is well above MLSS. Interesting that it’s only about double the 8% from anaerobic at FTP. Thx for sharing.
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You’re right, I should have clarified. I was referring to the maximal lactate steady state, where lactate production and lactate combustion are in balance. So to compare that to something functional, I guess around 60-minute power.
@DaveWh, yup your 7% and the 8% I’ve seen is of course practically the same. Really smart thinking that led you to that 7% figure!
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@Mikael_Eriksson @DaveWh awesome information guys!
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Nice when theory and practice align!
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