And what I'm saying, as a coach, is that this is absolutely NOT a relationship I have observed. Could there be a small correlation there? Yea, I'd buy it. Is it a strong correlation? Certainly not that I have observed.
I also have not found any literature addressing this concept. I'm not closed off to the idea that it might play a greater role than expected, but it goes against what I've observed and what I've heard from other coaches and athletes. If you want this to be a serious discussion, at least bring some literature to the table and we can speculate on what is being found.
This is all true. But it's missing some things. First among them is lots of ways to get to a 17:30 5k. You could do it off of a VO2 of maybe 40, if you had excellent running economy and a very high threshold as a percentage of VO2. You could also have a VO2 of 75 or 80, and struggle to run such a time, if you're running economy was poor. We've had top class elite athletes with VO2s as low as in the 60s, and with VO2 as high as in the 90s. There was NOT a massive difference in recovery between this athletes.
Interestingly, what is also seen is that there is often an inverse relationship between VO2 and efficiency. The guys with the highest VO2 are generally the least efficient and vice versa:
https://www.ncbi.nlm.nih.gov/pubmed/12471319How efficiently you run should not be effecting how your body recovers at rest. You're not running, so it's not a relevant factor. This implies, under your line of thinking, that a 13' guy with a VO2 of 65 should really struggle to handle a solid, elite training load, whereas a guy with a VO2 closer to 85 or 90 should devour the miles easily. Clayton, Shorter, Snell, etc. were all on the low end of VO2 max for elite guys (high 60s/low 70s) and had substantial, typical training loads.
Also relevant is that VO2 is a measure of maximal oxygen consumption. So sure, when we step up to 4:40 pace those elites have 40% more oxygen they can deliver. But, recovery is not a state requiring anywhere near maximal O2. It's higher O2 than baseline rested, but still much lower than say...going for a brisk walk. Both types of athletes have more than adequate oxygen delivery to meet the needs for recovery.
Obviously we need to talk duration and not mileage if we are talking about elite runners compared to 5k guys doing 17+ mins. An elite runner can easily do a session like 8xMile and come back for more in a day or two. That's usually about 40' of running, or perhaps 35'.
Now, most HSers or 18' 5k athletes aren't running pro hours, 12-15 a week. Most are probably on let's say 7 or 8. Call it 2/3 of what a pro does. So lets scale that on down, and we get instead of 35' of work about 25' of work. Which comes out to 6x1k at around 4:00/km pace, a sensible threshold value for a 18:00 5k runner. Can an 18' 5k HS athlete doing 40-50mpw handle 6x1k at threshold and come back in two days for more? Absolutely. Not even a question.
Now let's talk about the same 18' kid doing "pro hours", which I'm calling about 12/wk. M training is probably more, with some of the more speed oriented guys likely a touch less. For an 18' kid, this should average out around 8:30 pace, maybe 7 mph, so thats 85mpw. We are then talking about this athlete doing a session like 8x1200m at threshold, or around 4:50/1200m or like 6:30 pace. Big session? Sure. But can athletes, doing 85mpw handle such a session week in and week out? Again, yes.
This seems to be where you disagree, and admittedly you don't get many 18' HSers doing that kind of mileage. In my experience that's not due to breakdown. That's a result of most of the guys that bother to get to even 10 hours a week are guys that were good from the start. They were motivated. They were competing well and incentivized to train from the start. Guys with that talent, doing that kind of mileage, are usually already 14' or at least 15' performers. Some dedicated guys in 16's training like that. Almost nobody at 17'+ training like that, especially in HS range. Why? Because they probably started as guys running 24'+ mins near the back of the pack. That's demoralizing, and they just don't stick with it.
That said, I've coached plenty of 2:45-3:10 marathon types, as adults. There have been injury prone exceptions, but almost universally I've been able to get them up to 7-8 hours a week over a few years. Of adult runners, the biggest limiter is usually work/life/running balance. 10 hours is where it starts to be kinda "eh" for many people with a family and/or busy job, and 13-15 hours is really a big ask. That said, I've worked with at least half a dozen guys in that range, that have been able to handle multiple years of consistent training at that volume.
Again, I'm just not seeing, anecdotally or in literature, what you're claiming.
Bolded part is unquestionably true. But it might turn him into a 15:30 - 16:30 guy. Training is what makes talented runners fast, and untalented runners faster is the correct way to phrase that.
It will not, in my experience, lead to burnout (which is usually psychological, unless you're genuinely over-training someone, but you should notice that based on workout performance, HRV trends, PE, etc.), overtraining or injuries.
The key, and where most people get it wrong in my experience, is they try to get there too fast. Getting to those pro hours, especially in running, is probably a 5 or 6 year process minimum, and could be as long as 10 years. Equally as important, when I see most HS kids doing 70+ mpw, they tend to have easy runs at 6:xx and low 7:xx pace, with recovery runs maybe higher 7s or low 8s. That's booking for a 15:30 5k athlete if their intervals are true quality sessions. At that level, if you want to do intervals of the duration and intensity that the Ingebrigsten's are doing, it's too fast. The easier running needs to be more like 65% of HRMax, which is likely to be 7:30-8:30 pace. True recovery at 9+.