Sustained weakness, legs burning at higher cadences


I have a (pretty massive) sustained weakness. To the point that all my other 4DP powers are off the chart.
I have been testing as Sprinter, or as of lately of pursuiter.

The limiting factor to my sustained power, is that my legs hurt and get “blocked” on sustained efforts.
Especially when doing the recommended ~90 rpm cadence.

I did the building block plan for FTP, and the FTP progression workouts were horrible.
I risk to say worse than 9 hammers in RPE.

I would expect efforts at FTP to feel about manageable (tough but not super-tough for 6 minutes), as it is the power you would ideally hold for about 1 hour, but they just kill me.

When doing GOAT or Power Station or Cobbler, all is good, power is good, I can get good numbers.
Heart Rate goes up (I assume from the higher power, even though lower cadences).

If I a doing Defender or HHNF, or worse the FTP progression workouts, BAM legs get blocked, HR does not go as high.

From what is mentioned about cadence, this is not what I would expect. It is said that higher cadences for the same power, would create less muscular stress and more cardio stress, yet I feel the opposite.

From Wahoo’s blog :

"When you pedal faster, you put less strain (i.e. force) on your muscles with each stroke. You ride in a lower gear, and as a result, use your slow-twitch muscles. These muscles burn fat for fuel, are resistant to fatigue, and recover quickly when allowed to rest. Also, studies show a higher cadence means an increase in blood flow to the muscles – which in turn, means more oxygen in the blood and a higher aerobic performance.

On the other hand, a low cadence at a high gear is more taxing on the muscles. It uses fast-twitch muscles, which burn glycogen for fuel, fatigue quickly, and takes a long time to recover before they can be used again. In other words, muscle strength doesn’t last long, so you’ll start to feel the burn faster than at a higher cadence."

Could it be that my slow twitch are so lacking/untrained that they get fatigued faster than the fast-twitch ?
Or that my “FTP” is actually artificially higher on the tests (due to fast twitch contribution) and in fact the slow-twitch muscles are unable to produce those numbers ? ( I know that HM really overestimates my FTP, as I can’t get anywhere near those numbers on FF or complete workouts with it, can FF also overestimate FTP a bit ? ).
(That would mean I really really really suck at sustained power).

I feel that the legs are the limiting factor for my sustained power, not the lungs or heart, which could mean that a higher cadence would help, but it doesn’t.
I tried to include the strength training in order to help with muscular endurance, to see if I would get improvement on sustained power, but when also doing the strength workouts, I struggle even more to complete FTP workouts. I need about 1 week off the strength workouts to get back to the same sustained power.

What are the coaches recommendations for this ?

Do I lower the target a bit and stick with higher cadence ? or do I lower cadence and focus on power ?

Maybe a couple of “tempo” blocks before returnin to FTP blocks ? (same effect as lowering targets a bit I guess).
Do I go back a level or 2 in the strength program ?

I have followed some plans in the past, and saw improvements in MAP and AC, but sustained got stuck.

Curious - what is your relationship with Zone 2 workouts like? That is, have you a habit of going on 2, 3 or 4 hour rides?

Not lately, but I had no issues with zone 2 long duration.
I did some 24 hour rides and felt good. (Sustained issue was the same at the time).

That said, I have never been a fan or did much of called “base training”.
I was morbidly obese a couple years back when I started working out, so everything has always been high intensity for me, as when you are obese, even walking puts you in zone 4.

To further confuse me, if doing cadence builds or high cadence exercises I can rev up to 200rpm no issues, so leg speed is there.

Also, ISLAGIATT is one of my favorite workouts, Attacker (also mentioned to target FTP) is fine as well. (Fine as in I suffer, get tired, but complete and feel good about it). Defender is a complete different story. Feels much harder to me.

But there is something about sustaining power >95% of FTP, or worse the 101% in FTP progression.
I can do about 2 of the 6 minute intervals, but after that legs get blocked and I need either do drop target (10% should be enough) or take a few second breaks.

Also interesting, riding outside I can do an hour ride with IF 1.0 ( Normalized power equal, or even slightly greater than FTP without much problems). But can’t hold stable power around FTP for 20 minutes.
Even in Half Monty, the 20 minute “easy” part feels like the 20minute test from FF in terms of RPE.

I have been trying to chase this down for some time.
Considered bike fit could be an issue, but this occurs about on every bike, and not much change there after FIT updates.
Similar things happen to me when running (stryd) as well.
I do have a leg length issue, but it was a 0.8mm difference, so issue is mostly on the foot arch, and have custom insoles to address it, there still can be a functional difference due to the years without the correction, so my body could have adapted to it, and favored the other leg. Waiting on a spider powermeter to be able to check L/R balance. Currently I have a KICKR18, so measure of total power and a left crank powermeter, so it also can give an idea, and nothing major can be seen (nothing that can’t be explained due to precision and normal equipment differences).

Not sure if mental, or a fast switch / slow switch thing.
I am still overweight, so maybe that has a greater effect on circulation/cooling/confort than I would expect ?

A bit of a can of worms, trying to decide if I should do more strength training, or different kinds of it, or perform lower intensity base training ? Intervals are claimed to be better all-around…