Structural adaptations vs biochemical - where is crossover point?

I really enjoyed the discussion in the early Dec podcast about multi-year planning, pertaining to characterizing training adaptations as structural vs biochemical. Coach Trevor also used this simplified model in his recent article about why to take a yearly rest period. I get that a polarized Z1 / mid-top Z2 in Coggan zones is a great place for long rides to create long term structural adaptations. And that anaerobic training is more fleeting, in that the adaptations are more on the biochemical side. What about VO2 work, at say 105-115% of FTP? Realizing that none of this is binary - all structural or all biochemical - nevertheless, what would you say is the primary adaptive outcome of VO2 work? And thus, how much of it to include in base training phases (like now)?

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@TKskate, great question. I’m tagging @trevor on here for reference, but will give you my thoughts too.

Regarding the VO2 work, I would suggest the primary adaptive outcome of VO2 work in general is biochemical, including those peripheral adaptations for O2 delivery. I would also consider the way we are doing these intervals in terms of cadence, torque, etc. I tend to do my VO2 intervals on the mountain bike, so there is a decent change in the torque profile of that workout versus one done on a flatter section with the road bike. That’s where I would look at some of the structural adaptations as potentially taking on a greater relative role.

I do like to include some VO2 work during the base phase, but I think we need to be careful with just how much time is done. There are of course many ways to go about it. Personally, my usual 4-6x 4-5 min VO2 session is pretty hard and not something I do throughout the year. But I’ll include shorter segments during the base phase with shorter Tabata-style intervals or the occasional Zwift race or TT to hit that range.

Coach Ryan

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That’s a really good question and I think Ryan answered it well. The full answer is I’d love to dig deeper into the research on that question and I think it would make for a very interesting episode. I’ve added it to our list.

But short of doing further research, I agree with @ryan. I consider VO2 (or just above threshold) work as biochemical-adaptation-focused work. But I say that with an “asterix.” The asterix being that all work has both biochemical and structural benefits. It’s more a question of where are it’s primary adaptations and what are the costs.

In the case of VO2 work, it actually does produce structural gains. But if you isolate the structural adaptations, my argument would be that the stimulus isn’t any greater than a sub LT1 base aerobic ride. So gains are similar, but the stress and needed recovery is much greater with the VO2 work. So, when you’re focused on structural, more long term changes, you get a much better cost:benefit ratio with the base work.

That said, a little VO2 work to mix things up, produce some biochemical adaptations, and target adaptations through all pathways, has its benefits even in the base season. I’d just keep it limited. I also fully agree with Ryan - periodic shorter, more Tabata-style work does the same thing and doesn’t hurt nearly as much.


I think @trevor points out a key consideration to many of the discussions that we have on a daily basis on the forums, webinars, Q&A sessions, etc. What is the primary adaptation we are looking for. To my knowledge, there is no “on/off” switch as we transition into different areas of our metabolic “activation” so to speak, so it’s always a matter of primary vs. secondary, etc. adaptations.

Coach Ryan