15 hours is plenty my friend.
Here are two current snapshots of two people I have worked with for over 4 years.
They were 1st and 2nd at BC bike race in masters 40 plus (both in top 20 overall).
11-14 hours per week with the odd 15h week.
There fitness doesn’t change too much throughout the year actually, just a little more specific mtb work within 6 weeks of the races.
Thanks for sharing @steveneal . Seeing real-life data helps to understand what training delivers, so much better than research on college students 
@fazel2: my modality is speed skating, not cycling. That is a difference. Maybe also age (44).
A recent ramp test on the smart training suggested an FTP of 270, somewhat similar to what i can do on inline skates in zone 3 now. But i don’t think i can hold 270 on the bike for an hour.
A critical power test resulted in a CP of 336 watts…today i tried to climb a virtual hill on 330, i was done after 5 minutes and did the rest of the hour at 160 watts 
(hr zone 1…)
I go on the premise that fast twitch muscle fibres create lactate and slow twitch muscle fibres gobble it up. The more of that low intensity you do the better you slow twitch are at gobbling it up as fuel.
In other words you don’t produce less lactate at higher intensity, you are just better at clearing it.
Wait - they can measure power on speed skating? Heiden supposedly did this climb in 14:10. That must have been an ungodly amount of power at his weight.
If you really want to go down a rabbit hole consider the construction of “over-under” type intervals by coaches who favor threshold training and “lactate clearance” workouts by those who shy away from it. The former are typically set up just above and below threshold, like 95% and 105% and of equal duration (2m above, 2m below). The latter typically utilizes a much larger range; a short building period (something like 45s @ 120%) followed by a longer clearing period, e.g., 2m15s @ 80-85%.
@fazal1010: power is measured by deriving it from accelerated mass, using GPS speed, wind speed (weather forecast) and direction and barometer (for elevation changes). The same thing as what Strava does. Not as precise as a power meter, but precise enough to detect week by week trends or pace a race.
@fazal1010: some of my pears only train 3 times 1 hour a week in a HIIT type training. They usually out skate me in speed work. However, when I taper to match their rest, they are history.
This could apply to your 15 hours too. They will give you ‘a base level of fatigue’ that needs to clear before you can harvest the results of that training.
I am starting to think that if you do <4 hours a week, spread it out through the week and go as hard as you can. This will give significant gains but also a ‘fast to reach plateau’.
4 - 8 hours, you need polarization to make it through the week, but you’ll only see the effect if you taper. Less perceived progress than 4 hours of HIIT, but a higher plateau.
8+ hours, same thing. Careful planning is required as well as tapering to see the result.
I was pretty dissatisfied after my Christmas training camp experiment where i added 6 hours of z1 cycling on top of the 6 normal hours. I did not see the gains I was expecting based on that COPID training. However, after two weeks back at ‘normal volume’, i am starting to notice a few positive effects:
So i’ll keep the z1 cycling as a means of recovery, on the same day as ‘normal’ training. Too bad i have a job, so that only works in the weekends.
No rabbit holes for me.
Whilst interested in what’s happening I subscribe to the less is more approach to training. Not in terms of volume and frequency but in terms of complexity. Keep it simple enough it’s hard to get a sesssion on the bike wrong.
I’m not one of those who gets bored and needs to constantly vary the effort every few minutes.
I feel the same way. I’ve cancelled my Zwift subscription, and though I have workouts planned and synced, I tend to run everything in slope mode, do my own warm-up, etc. This is more organic. It allows me to start efforts when I feel ready, moderate power appropriately, and add volume or intensity to the end of the workout if I’m feeling good. Besides, for anything other than endurance work I feel like ERG is jerking me around.
I’m a big fan of slope mode. Very versatile where you’re not sure of the exact effort you’ll be able to manage and how long and how many sets but know where you want to aim for. Plus you never fail a workout, or end up in the erg spiral of death.
Plus to add, these 3 x 20 min @steveneal tempo intervals would work well on slope mode (in my opinion) where you regulate power through cadence and or gearing keeping an eye on your HR and letting the power be what it is.
At my peak (2019), I’m wasn’t that far off those values, with 400-450 hours per annum (22500 TSS). That’s about 8-10 hours peaking at 11.5 hours. Maybe it’s a 40+ thing 
Not good enough to podium, though; just enough to be at the pointy end of the race. That’s good enough for me.
awesome! Any part of an event is fun and the pointy end gets very fun nice work
Today I performed 75 minutes of SFM training (@steveneal Fatmax Magic )
It was 5x10 minutes in HR zone 3.
I noticed a few interesting things:
I love the names coming out of this thread…some fun things for riding / skating steady
I won’t comment on muscle fibre type as I have no proof.
Steve
So after 5 min test yesterday it was time for a 20 min today… +10w /3.5% in 20 min AP, so not quite the same % change as my 5 min, but still a good result.
Interesting that it feels like it’s my breathing that is the limiting factor now. I’ve noticed in a couple of sessions that my legs feel strong and little of the usual lactate ‘burn’ and they certainly didn’t feel like they were the limiting factor for me today and it felt like it was my breathing approaching vo2 max that was the killer.
Could this be pointing to a need for more vo2 work? Its on my plan for a block in a few weeks, but is something I have done little of in the last few years. My 20m power is 83% and my estimated FTP (WKO/Intervals.icu) is 80%. Any thoughts?
Edit: I should add I have a 4 week block of threshold sessions planned next followed by a block of vo2 work. 2/week with the rest z2 work.
How long was the block that brought these improvements?
@steveneal this last block was 3 months pretty much to the day. Lots of 2-4hr z2 work and 2-3 times a week I did tempo work, but as I mentioned before it would have been in classic Coggan z3 zone and mostly above your suggested HR cap. I did tempo work ranging from 3x20 to 1x80 intervals and worked a range of cadences but I tended to work top of the zone and more like 88-89% max HR.
Before that I did a LOT of z2 long endurance work last year with little intensity really. Typically 12-20hr weeks outdoor steady rides exploring the countryside and accumulating miles! Probably safe to say my only >FTP efforts came from steep hills on the routes. I didnt do any structured training in the last half of last year and most of what I did before that was <=FTP work. I’ve always been a wimp when it comes to hitting the VO2 ugliness but thats going to change this year!
Ok , still pretty good improvement, I really look for a consistent 5-7% per year so I think your results seem quite good.
Few things.
Do you FEEL a lot better during the tempo and long endurance rides?
Have you done any racing on zwift at all in last 4-8 weeks?
If motivation for hard training is there, and I understand that, how about trying a few races a week?
The other thing I notice in clients I work with is the real results come when they start racing, recover quickly and can really train and build during the first portion of a race season. Then adding racing more into the mix and backing off the tempo they really tend to do well.
There is nothing wrong with a few weeks of harder training, it will help you and likely won’t hurt.
I would recommend you move to endurance and hard intervals above threshold or races.
The other type of hard riding I find works well if it is planned is one group ride a week that is hard but you can be in the mix, the other group ride with a harder group ride that you can’t last the entire ride (get dropped) but work as hard as you can until that happens.
Thanks Steve - really appreciate your input.
A few answers:
I should have said that I’m not a racer - my goals are the Liege Bastogne Liege 100 mile hilly sportive in April, a hilly 200 miler c2c in mid June and a week smashing across the Dolomite mountains and the Stelvio in mid July. Its about endurance for me but combined with being able to be strong across a tough day of hills and tempo up 8-12,000 ft of mountains per day.
I do feel strong. 3-4hr endurance rides feel easy now and recovering after hills etc is quick and easy. My ride partners always mention how strong I am. When I fuel right I can really push on with tempo rides (and doing them harder than your HR cap type of rides). I didnt have any issue with pushing 80 mins at top of z3 and was able to still go harder than planned if needed. I often ride a 3hr endurance ride with a couple of friends and then ride 30-40 mins steady tempo home at the end and feel great.
I like the idea of hard intervals and endurance. My plan calls for 2x 100% FTP sessions a week and I think these will be quite tough at the new higher FTP. Then its 2-3x a week various length vo2 sessions for a few weeks. Final block is a new one on me and combines ‘race winning move’ sessions of sprint/>FTP/sprint intervals, along with sessions of 2-3 repeats of 5-6 x1min vo2 reps
straight into 20-30min tempo. I think this is going to give me a solid 3 months of intensity along with easy endurance riding leading up to LBL in late April.
Huge difference for me this year is I’m very ready and looking forward to ramping up the intensity. This will be a whole new experience for me but I’m really looking forward to it right now.
We dont have quite the same type of group rides around here, as most are no-drop group rides of different levels. I could probably create a pretty tough weekend group ride with a few local friends that would be hard but doable. Up to now we’ve used these for longer and disciplined endurance rides but I have a few buddies that are strong riders and simply cannot stay disciplined, so would be good candidates for a tough day out!
After LBL I was thinking of switching back to a plan similar to what you described above - 1 day of MAP based intervals (I need to understand these better), 2 days of easy tempo and lots of z2. Hoping that might be a good bridge into a week in the mountains?
Any other thoughts appreciated.
