The usual advice is to do Zone 2 endurance rides at 65–75% of FTP. I’ve often wondered if there would be any training benefit to always doing these rides right at the upper end of Zone 2 (without straying into Zone 3/tempo)? Easy enough to do on a trainer with ERG mode and target watts. If you stay below the first ventilatory threshold, presumably you wouldn’t incur the additional hormonal stress and fatigue, but you might get more training bang for your buck?
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My understanding of the physiology was that as long as you’re below that ventilatory threshold then you’re within the limits of those base miles, so I did tend to work close to it. My thinking being if it’s not detrimental then the fact it “felt” that little bit tougher etc meant it made me believe it was doing me more good.
Now wait for someone to reply who actually knows what they’re talking about lol 
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I have read several different books about training and used Carmichael’s CTS in its first 2 years when it was cheap. They all seem just a little different in the calculation of the upper end of endurance rides. For example, CTS used heart rate of 87% of MAP as the top end of endurance rides and added that one could have 4 minutes above that rate on a 2+ hour ride and still be ok. Looking at my Sufferfest zones, that would mean I could ride the whole time in the lower end of zone 3 and be fine. Go figure.
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First question: when you say “more training bang for your buck” what are you trying to achieve? If this is about improving FTP, I suggest you listen to several of the podcasts from Empirical Cycling: Empirical Cycling - Podcast Episodes.
Specifically, the ones entitled: FTP Testing, FTP vs. VO2 Max, , Effective FTP Training, Why Everything You Know about VO2Max Power is Probably Wrong, and Listener Questions about FTP Training
You cannot get more benefit by doing less work. If you want to make the ride easier at 65-75% of FTP, you will need to raise your FTP, or improve your Time to Exhaustion at FTP. If you want to improve your endurance at the upper end of Zone 2, you would probably have to ride so long that the fatigue would be the same as an FTP workout. The same would apply to a threshold ride.
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My interpretation on whether you do it in upper or lower end of Z2 would depend on your current total load. If you are coming from consecutive hard sessions and a high level of fatigue you do the low end, opposite you do the high.
Heck, it may even come down to just how you feel there and then. Good legs? Go for it! Tired legs? Chillax at 65%.
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Thanks for the link to the podcast. No, it’s because I follow a polarised training plan where only two or at most three days each week include high-intensity intervals, and the rest are exclusively Zone 2 endurance. So I’m trying to maximise the benefit from the Zone 2 days.
I would agree that an endurance workout has to be (significantly) longer than a ss/threshold/vo2max workout BUT I doubt that the accumulated fatigue has to be the same. In fact I (personally) can accumulate a lot more TSS without getting overreached by doing exclusively endurance then when I add HIT.
Moreover I‘d argue that the most (ok, one of the most) important adaptation for beginners/intermediates comes from easy endurance → mitochondrial density.
Now I go with @aerobrain and am curious what someone with a better grasp of training theorie will add 
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If you are beginner, any exercise will give you improvements, and certainly will give you the mitochondrial benefits you mention.
While I would never doubt your perceived efforts, the principle of there is no such thing as free lunch would argue against getting more benefit with less effort/fatigue. I would guess that because the fatigue is distributed over a greater time in an endurance effort than HIT, it feels easier.
If you want someone with a better grasp on training theory, listen to the Empirical Cycling podcasts: Empirical Cycling - Podcast Episodes.
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Roger - what is your goal event? Or general goal?
I want to be clear. I should have written: someone with a better grasp of training theorie THAN ME 
I always appreciate your input and meant no offense at all.
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I took absolutely no offense at all. I am not an expert, so I wanted to share a resource that I have found very useful. In fact, it was @devolikewhoa who pointed out this podcast: RPE vs absolute power vs generating body heat - #2 by devolikewhoa
@wmalexmann — My goal is to get as fast as I can for multi-hour endurance rides and events. For example, I’m doing a >100km gravel race next month. I’ve been cycling for 20 years but have only been doing structured training for a bit over a year.
@Heretic — I completely agree that training above lactate threshold is a great way to increase power across all zones. I routinely do 2–3 days of high intensity work each week (last week I did 5 hard days, kicking off the first week of a block-periodised month). But there is extensive evidence that polarised approaches with considerable time in Zone 2 are among the very best ways to train for endurance. And, in fact, training in Zone 2 itself is great for increasing your aerobic threshold (i.e., ventilatory threshold 1).
For the purposes of my query, we can assume that Zone 2 rides are essential. That said, my specific question was about the possible training advantages of mainly doing these Zone 2 rides right at the very upper end of of the zone (e.g., 75% of FTP) rather than hovering around the middle of the zone (e.g., 65% of FTP). Advantageous? Or not?
I can see the advantage of recommending 65% of FTP when doing these rides outdoors, because otherwise it would be too easy to creep into Zone 3 (tempo). But on a smart trainer, you can set the power and just ride!
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OK, so not a expert on this but love the question so here’s my 2 cents worth until someone who has the definitive answer does chime in:
The moment I first read the question I heard the Coaches’ voices ringing in my ear - “Harder is not always better.”
With Zone 2 efforts, HR and RPE become really important - any changes in % FTP should not take you out of the correct HR and RPE zones. %FTP, HR and RPE won’t always share a constant relationship from one Z2 workout to the next (fatigue/ stress/ heat/ nutrition etc) so a correct Zone 2 ride involves being aware of all 3 (arguably RPE most important as it’s an “all day pace”). Of the 3 changing %FTP is how you’d keep in Z2 if drifting out (assuming well hydrated/ fed/ not overheating etc). Taken from the notes accompanying Endurance +:
“So what does a “proper” Zone 2 ride look like?
For 90% of the ride, you should stay between 55% and 65% of your FTP, at times going up to 70%, but not over. (To spice things up, we have broken this session into 10-minute segments alternating from 60 to 65% of FTP.)
*Your heart rate should be sitting in mid to low Zone 2 heart rate, which is 70-80% of LTHR, up to 85% of LTHR, but not for long. *
It would be best if you held the highest comfortable cadence you can, for most this is 80-90rpm
Also, your RPE should be a 2-3
Sounds simple right? It’s actually one of the harder sessions to get right because you spend most of the time questioning why you are riding so easy, and if this is really going to make you fitter and faster. You will have to trust us on that one!”
So my opinion on your specific query: for Zone 2 workouts a 5% increase in duration is far more beneficial than a 5% increase in intensity (to hit the Z2 ceiling). And a 5% increase in intensity carries too great a risk of fatigue having an overall negative effect on training (carrying fatigue into subsequent workouts).
As always, happy to be corrected and educated!
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Hi Craig, thanks for digging out those very pertinent quotes from the Endurance+ workout notes! It certainly looks like the experts at Sufferfest don’t recommend my top-of-Zone-2 strategy at all. I wonder if any of the coaches would be willing to chime in to explain why it’s preferable to main sit right in the middle of the endurance zone? Is it about minimising fatigue? And is there any scientific research in this area, or is it based on their analysis of the Sufferfest user data?
I wish I could offer expertise, but all I have is personal preference based on reading, coaching high school distance runners, and experience on the bike.
- There is no way I can do long slow distance rides indoors, unless I have an awesome movie to watch and time off the bike to massage my aching rear end.
- If I kept my HR at 80% of LT on outdoor endurance rides (which I think of as active recovery sort of), I would go nuts. I just ride at a pace that would allow me to talk to people I am riding with and try to keep my attention on the countryside. I don’t worry unless I catch myself - when I ride solo - racing along when the road is smooth and empty. So far, so good.
I am more careful when I ride centuries. I make sure to keep my effort in zone 2 as much as possible early on so I can finish strong with a decent average speed. I am not a racer, just love the bike, the views along the way and the challenge of going a bit faster than the last time.
Thanks all for your input and knowledge here in regard to @roger’s question. I can’t personally say I have any specific research information to support staying in the middle of zone 2, however I don’t recommend trying to do your zone 2 training at the upper end of it. I think really, it comes down to minimizing fatigue and making sure you accomplish the goal of the day’s workout. If that’s a recovery ride, then you ride embarrassingly slow. If it’s an aerobic ride, you monitor all of your metrics- HR, power, RPE, etc. and make sure you’re in that aerobic zone and not pushing into zone 3. Like @Craig.Quarmby pointed out, just because you’re in zone 2 for power doesn’t mean your HR is in zone 2, and we know that HR can be an indicator of fatigue, under-recovery, stress, etc.
Let’s remember the purpose of zone 2 training- building aerobic and muscular endurance without creating much fatigue. Sure, zone 3 has its own benefits, but it’s also the point at which you begin to build fatigue right? And it’s SO easy to cross that line of aerobic/zone 2 effort into low zone 3 without even realizing it until you start to feel a little fatigue creep in. As far as I know, you don’t build any MORE mitochondria in high zone 2 than mid zone 2, but you WILL create more fatigue. So why take that chance? Creating fatigue on a day that’s supposed to keep fatigue levels low will only hinder your ability to hit your hard workouts HARD - which is the point of polarized training, right? Easy days are EASY and hard days are HARD.
It would be better to stay in mid zone 2, where your body is efficient at burning fat, building mitochondria and training MCT-1 transporters which are critical to lactate clearance. These MCT-1 transporters actually bring lactate into the mitochondria within the Type 1 muscle fibers where it’s processed and reused for energy. All of this happens much more efficiently when the body isn’t stressed and has plenty of oxygen to utilize.
Bottom line, I think training at the high end of zone 2 poses more risk than reward. Too easy to creep into zone 3, and your body will be slightly more stressed and less efficient at doing all those important physiological processes that are supposed to make it better. So let’s not take that chance and just enjoy riding our bikes while taking in the scenery or chatting with some friends while we make our bodies more aerobically efficient!
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Thanks @Coach.Suzie.S for your detailed and thoughtful explanation! Your reasoning makes a lot of sense.
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Further appreciation @Coach.Suzie.S - the input and support from you and your colleagues on these forums is just outstanding.
Here is a podcast that adds further to the discussion - from a sports scientist at the University of Cape Town. Always packed with science and studies, in this episode Ross Tucker discusses his experience when working with top Kenyan marathoners and the pace the majority of their training runs were run at. Well worth a listen.
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Just yesterday, I heard about the benefits of zone 2 rides in this week’s GCN show. That made me search this forum for the term mitochondria because, in the show, they were referring to Tadej Pogacar’s trainer stating that building mitochondria are essential. So now I wonder how often I should do zone 2 rides, and I wonder how long one zone 2 ride should be to give me the benefits of building more mitochondria. In the SYSTM app, there are some “Inspiration” videos that I would see as zone 2 trainings. But these are about 1 to 1.5 hours, often shorter. I wonder if these would still be beneficial enough. I would still prefer to do Z2 rides outdoors, but sometimes (especially in the winter months), it’s just not doable because of temperatures and not enough daylight time.
What are the coaches’ opinions on that matter, @Coach.Suzie.S?
Maybe the topic would also make another insightful episode for the knowledge podcast @Coach.Neal.H @Coach.Mac.C?
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Look up Polarized Training and Dr. Stephen Seiler.
Because this takes lots of time, it’s not something the SYSTM planners particularly ascribe to as their focus is on the time crunched cyclist.