Sweet spot is a pretty narrow band within “Zone 2”.
This is very true, and a good point. I think a lot of the FUD and swirl around this for me stems from this very notion. There is nothing inherently wrong with any particular zone. They are just tools to try to help dose some training stress to a particular physiological system. Despite it being a narrow band though, a “threshold-oriented” approach has you spending a TON of time in the narrow strip of the zone (yes, in a progressive way, and yes, you can adjust down, but a lot of attention to that system nonetheless).
Studies are not going to match training plans and expectations because they are short, narrowly focused, and diligent about confounding variables. And they’re not interested in you succeeding as an athlete. I haven’t seen any study (be it POL, THR, or both) where they have subjects train like ppl actually train.
It’s funny because I just finished a draft of my next 3-4 cycles of training (each 14 days). I did not set out to “do the POL” or “SST”. I didn’t think about intensity distribution, “sweet spot out the wazoo”, or any of that ahead of time. Heck, it’s not even linearly periodized blocks because I don’t train for an A race/event that might dictate base->build->peak. I have a “road season” that I ride through.
I plugged in the main/breakthrough “workouts” within the cycle (14days), workouts that really work the areas I want to train based on time-frame, goals, limiters, and just standard training concepts (e.g. vo2max work helps everybody, to a point). I then fleshed out everything in between with “rides” (in TR speak, endurance/zone2 stuff of varying length, zone1/2 recovery, or a combination…basically low, talk-test intensity).
The “workouts” are more precisely defined (HR and power). The “rides” are mostly HR/duration driven but I have an eye on power as well.
I’m sure somebody would look at the outlined plan and just doing some quick numbers say “looks like a polarized/stretched/wide/whatever distribution…nice, looks like you have an eye to not overreaching, absorbing training, etc”. An astute observer would counter: "well, I certainly see a some up-tempo/‘sweet spot’ in there…doesn’t look like the polarized I know’.
We seem to be trying to take how athletes have trained and based on how we characterize that training after the fact, superimpose those patterns on how we design our plans before the fact. I doubt any of those athletes and coaches sat down and talked about it that way. I bet they did it more like the way I did it…except, you know, better. 
Anyway, I’m the OP and I was asking the wrong questions and thinking about it the wrong way.
THR? POL? None of the above
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Although I agree regarding the theory that SST might not give the best fat-burning response, I have had my fat burning tested a few times. Once while relatively untrained at the start of 2015 (220W FTP, and peak fat burning at around 25% of energy); a couple of months later 240W FTP and 50% fat. I started TrainerRoad and found out about Sweet Spot training after this, and followed the sweet spot plans into 2016. I tested again. 280W FTP and 75% peak fat burning.
I should add that I was doing some long rides as well, but I was doing the long rides in 2015. I did more long distance in 2015 and less in 2016, and more sweet spot, and I had a higher FTP /and/ more fat burning.
N=1 of course, but I did feel it was going the right way. Maybe to get the absolute best aerobic metabolism I’d have been better served with a more polarised approach but I got a long way on SST.
Measuring CO2 exhalation in parallel with oxygen consumption during a ramp test gives an estimate of fat/carb ratio.
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A few comments below, perhaps I misread/misunderstood the post…
Studies are not going to match training plans and expectations because they are short, narrowly focused, and diligent about confounding variables. And they’re not interested in you succeeding as an athlete. I haven’t seen any study (be it POL, THR, or both) where they have subjects train like ppl actually train .
I would disagree with this. I think the things we do in the applied labs are trying to do this. While we have to control variables, we want to have outcomes that inform the practice that athletes do. You see this in studies from guys like Stephen Seiler, Paul Laursen, Dan Plews to name a few. In fact, recent studies by Seiler have used 4, 8, 16 min intervals at self-selected paces to mimic how people train.
It’s funny because I just finished a draft of my next 3-4 cycles of training (each 14 days). I did not set out to “do the POL” or “SST”. I didn’t think about intensity distribution, “sweet spot out the wazoo”, or any of that ahead of time. Heck, it’s not even linearly periodized blocks because I don’t train for an A race/event that might dictate base->build->peak. I have a “road season” that I ride through.
There is a substantial body of work suggesting that planning with frequency/volume, high-intensity training, and training-intensity distribution can have a substantial impact on performance outcomes. See Seiler’s Hierarchy or Endurance Training Needs
We seem to be trying to take how athletes have trained and based on how we characterize that training after the fact , superimpose those patterns on how we design our plans before the fact . I doubt any of those athletes and coaches sat down and talked about it that way.
I’m confused here, if we don’t look at ‘what was done’ how will we know ‘what works’? Seems like there would be missed opportunities for efficient training if we didn’t. For example, if we know the physiological system that we want to impact to improve performance, previous training studies/experience show us the most efficient ways to do it. There is support for both THR approaches and POL approaches. One can make adaptations to VO2max, for example with some HIIT work, but HIIT work isn’t as impactful on improving efficiency.
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https://fascatcoaching.com/how-i-invented-sweet-spot-training/
Right around 41:30. Good enough for me.
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I listened to that podcast while traveling over the holidays. I thought it was a good listen.
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I listened to it right around Christmas. I like Frank Overton’s content. Even though this thread is basically dead, I posted it because it basically answered my original question.
I’ve listened to this a couple times recently. I’m a fan of Frank’s content as well as his approach. He tends to take a very wholistic and athlete centered approach.
While he may be Mr. SST, he also often credits all of the polarized style training (20-30hr weeks) he did early in his career for laying a lot of the foundation. His plans typically involve much less of the high intensity work, outside of preseason race prep, than the popular TR, time crunched type of plans. I find listening to him and folks like Seiler to be a nice balance to the hyper structured intervals and FTP obsessed approach that most of the indoor programs seem to embrace, and I mix and match as suits my needs.
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I enjoyed that podcast episode, thanks for sharing 
I must say he makes a pretty compelling argument for sweetspot training.
The only thing that nags at me is on the other side you’ve also got some very credible people stating that the majority of the magical aerobic gains (improvements in capillary density and mitochondrial density etc.) occur at an intensity below LT1.
Yep, I hear ya. Hence all the spirited debate! (which I’ve enjoyed and learned from).
edit: just went back and looked at what I did back when I went through one of FasCat’s sweet spot plans (2 summers ago). I didn’t know it at the time, but I still spent quite a bit of time at or around LT1 what I can only guess is close to LT1 on those Zone 2 (and low Zone 3) rides. With his approach, you ride sweet spot as much as you can, but there’s quite a bit of Tempo and Endurance too.
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Here’s what Xert has to say about it:
Conclusion
Sweetspot training, when used by some athletes and for the right purposes, provides an excellent way to train. However, for many athletes, SST amounts to the black hole of training, where it’s too hard/short to provide endurance training benefits. Many athletes fall in-between, where depending on the specific intensity the SST falls into and its relationship to LTP and their training goals, will determine whether it is a wise training choice or not.
In otherwords, there is no “best” training method – match your process to your outcome.
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Here is some new material, Dylan Johnson reviews papers comparing sweet spot and polarized. He doesn’t mention TR specifically, but with with the SSB plans it does really concern us.
From his literature review, there is no clear evidence that SSB is superior. Actually the polarized model shows better results. This makes me curious which scientific papers our TR head coach or fellow users may quote. I’m hoping we have good material, because I’m kind of SSB religious. But the training needs to be evidence based. So where are the articles showing SSB superiority?
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“The hard enough to drop you zone” – Backwards Hat Dylan
We can all agree on this! BHD droppin’ the wisdom.
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On a more serious note, this has been discussed many many times on the forum here (but not really this thread). I think my original question was posed before ppl were really ready to discuss (or even knew where to find answers). There is a podcast where Frank Overton (Fascat) discusses the “origin of sweet spot training”. That is probably as good a place to start as any because anything that came after that is highly derivative of the work he and the other coaches and athletes were doing at the time (they were working on what would become the Performance Management Chart in Training Peaks).
https://www.trainerroad.com/forum/search?q=%23training%20tags:polarized
^^^ stole that link from @mcneese.chad , so seems legit ^^^
For me, even if there is an advantage to polarized training and just not prepared to spend hours in"z1" anymore. I’d be happy to swap a ss session for a z1 to prevent burn out, which is a good idea at 50+ anyway and is within the TR ethos.
Also, TR plans don’t just keep us in SS.
I geuss it’s what we choose to fit in with our life.
Good to be informed though 
Keep in mind, the alternative to sweet spot training isn’t polarized. There are a number of other approaches to training that are mindful of an athlete’s time. You just have to dig a little deeper and get out of the “SST vs. POL” mindset. It’s not necessarily one or the other and it’s not a zero sum game, either. My training would not be considered polarized, although I try to log as many miles at or below LT1 as possible.
Fun fact, back when I posted this, I actually almost titled it “So what ever happened to riding tempo?”, but coming from a running background the word “tempo” carries just as much baggage and confusion as “polarized” does to cyclists.