Minimum intensity for aerobic gains

Hello forum,

Quick question on intensity, what is the lowest percentage of FTP you can go to in order to elicit aerobic gains that you would commonly associate with Z2? Such as mitochondrial biogenesis and enhances metabolic efficiency etc.

I’d assume the point between Z1 and Z2 but I’d like to hear your thoughts?

Thanks in advance

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It depends how long you ride…it’s totally possible to improve aerobically when riding in z1, but might take a long time.

The minimum training intensity for improvements in aerobic power is usually stated to be about 50% of VO2max. That would be about 60-65% of FTP for the average cyclist. The exact threshold is going to vary considerably, however, depending the particular adaptation in question, initial fitness, etc.

Since you mentioned mitochondrial biogenesis specifically, keep in mind that it is hard to apply the notion of intensity at the single motor unit level, as either a motor unit is activated, or it isn’t (ignoring rate coding, of course, but that really seems to come into play at very high intensities).

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Yeah, I have almost unlimited time to train so low Z2 is what I was thinking of.

If somebody truly has unlimited time to train, it would be hard to do much else.

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Agreed, the adaptions are accelerated at those higher intensities, 67%~ is what I was thinking in terms of more prolonged durations.

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my vote is 65%. actually just had a really high level athlete ask this same question, as I commented in one of his rides that I was curious why his endurance riding was so low. he replied:

Training over the past decade+ has always been an optimization problem for me, especially in terms of recovery. One of the cornerstones of my training pedagogy (in the past) has been to go as easy as I can while still eliciting the maximum training effect (on days where the point is not to smash, ie z2) so that I don’t accumulate unnecessary fatigue.

The way I have interpreted z2 is that it’s a band with fuzzy boundaries where for the most part you’re eliciting the same metabolic adaptation across the entire span of the zone (iLevels have me between 212 and 288W!). The difference across the the training band being that as you produce more watts, the muscular component of the pedal stroke comes more into play and while do you probably gain some muscular adaptation from harder z2, I’d think that it would be minimal compared to doing focused high torque or just lifting as we are. What are your thoughts on this? Would love to hear your reasoning for going harder in z2. Obviously 260 - 280W is not “hard” but day in and day out it’s def going to accumulate more fatigue and the benefit over going easier in the same endurance zone is unclear to me. If I’m missing out on some important opportunities for physiological adaptation, I wanna know! Sorry for the long email.

my reply to him was:

great question, and no worries on a long email; it’s a good one!

you nailed it, somewhat fuzzy. 212 to 288 is a huge gap, right!? i mean, if you’re at 210 then, where are you really at? Is it “recovery”, or “endurance”? The lines obviously blur.

Here’s my thought process, and def want to hear your thoughts. You’re a ridiculous athlete with a ton of credentials; you’ve done something right to get to where you are at, so I’m always open to hear a different perspective than what is mine!

i’ve always erred closer to 70-75% ftp, but i don’t want to say “i did this, so you have to”. here’s why I go harder.

I’d really only say that an athlete is riding endurance too hard if they aren’t able to hit high watts in really hard sessions during the season. But Right now, there aren’t really hard sessions, so I personally think it’s better to reap as much reward as possible from higher endurance.

you’ll notice during vo2max blocks I’ll specifically say “ride at 65% FTP for endurance and SAVE IT for the vo2 work”

If we go wayyyy back at look at the Coggan adaptations chart, I’d rather be closer to tempo than recovery while the riding is purely aerobic and pretty simple. More glycogen storage and interconversion of fast twitch muscle fibers. I personally don’t feel overly fatigued from riding like that, but if you feel that 60% is better for you, I’m open to it.

Also, while there’s no way to test it aside from just anecdotally how you feel (which IMO is SUPER valuable, but some athletes NEED to see a # to believe something), i dont think you’d accumulate that much lingering fatigue especially with full on rest weeks that have 5 days of easy rides. You are a unique individual, as we all are, so I’m totally okay if you want to go easier.

So keep rolling with what feels right; end of the day I do want you to make a decision like this since you are experienced with your body and performance…maybe meet halfway at 65% and see how you feel?

I just think you’d get more out of it without having the fatigue. now if you were blasting tempo all winter I’d have a mega issue with that. So for devil’s advocate, we can circle back to the first question, well if its 295 vs 288 what are you at?

250-260 IMO is what I’d go for, but lmk what you think!

Good luck!