Anaerobic capacity....somewhat confusing term, I'll give my take/understanding...
Near exhaustive training has its place. The author also states that you can do a near to nearly exhausted, a milder version. If you further reduce that argument - to a very mild version, there is a relationship to the frequency and intensity of the 'workout'. Broadly, intensity and frequency are inversely proportional....recovery post session is longer the more intense the session is. And the length of recovery comes with its own set of variables - training history, current state, age, current life stress and life circumstances. There are those that need to be in a state of readiness v recreational athletes v pro athletes: 3 distinct populations that could be further divided into sub sets. And then there is generalist v specialist. Never a one size fits all. Oh and the untrained, those that are ill with compromised health which shine a light into energy production.
So caveats dealt with and pushed aside....
Question is, is it appropriate for your 'training'?
Workout and training in quotes because both words are used in the article and so it follows what is the purpose of close to exhaustive training.
Working out could be training or it could be just, er working out.
The article very loosely offers it as a time efficient proxy for steady state tempo running, that is running at above aerobic threshold at a steady state for a given time v running at a much higher intensity but using rest recovery as an interval instead....so does it illicit the same adaptation?...at least that is what I think it says and what I interpret the question to be.
What it doesn't say, maybe the paper does, is power output. And that matters.
It matters because of muscle fibre recruitment.
Anaerobic power v anaerobic capacity? We are limited by physiology and once phosphate is fizzed up, the only way to maintain high power is anaerobic glycolysis. The phosphate is being replenished to a minimal amount if that power output is dialled back. And then boosted during rest.
And from here we meander into mitochondria ....mitochondrial biogenesis and respiration, fibre type and the stress response to training.
Anaerobic capacity is a function of aerobic capacity. The capacity, although anaerobic at the time of effort, should illicit adaptations that results in greater aerobic capacity by boosting aerobic threshold...improved systemic lactate buffering and fuel use, increasing mitochndria etc.
The desired outcome: aerobic function at higher intensities is an improvement in aerobic capacity, not anaerobic capacity but via anaerobic work.
If, via inadequate recovery and/or doing so too often, aerobic function stalls: mitochondria are not built back up or repaired (the recovery process is compromised) and the adaptation is prevented or at least not optimal.
It then becomes an exercise of excessive stress, overtraining leading to what is called by some aerobic dysfunction. Or perhaps, a plateau....null improvement.
Do the same thing again and again in an unrecoverable state and you plough through the work by anaerobic glycolysis, again. Anaerobic capacity has a limit, aerobic energy is unlimited in an exercise sense (other limits affect fatigue). Well, we do have a limit....about 85 years if lucky.
So important: frequency matters. If exhaustive exercise is good it can only be positive if and only if recovery is on point. And that varies.
Improving aerobic capacity is the aim via trips into anaerobic territory. It is a matter of dosage and timing linked to frequency, duration and power/intensity.
So...steady state over threshold produces lactate, higher powered intervals do too so is one better than the other, if recovery variables are equated? Dunno.
Do you run to workout or train? There's your answer, probably. Do you run because running is a component of the sport you do or do you run because running is your sport?
There's a difference. If you need recovery ability for a game that you play to near exhaustion - then near exhaustive running intervals for pre-season prep tick that box. And a way to be a more efficient runner is to be a better runner. Efficiency gains via vomiting or graceful movement?
Big fan of intervals but not exhaustive, even though, ahem, I've indulged.
I sprint competitively and do, well, intervals. Sometimes I, ahem, do so to exhaustion you could say but....I exhaust my power output, stop and go home.
This is the difference between anaerobic power and capacity....the greater the power output, the greater the available capacity, that is it enables the highest power output for the longest time, which isn't very long....300m and then it is how much death one can handle.
Now take your foot off the gas, curb power output, run slower but above aerobic threshold to employ glucose and lactate, the adaptive process tends towards aerobic capacity....as mentioned earlier. You have a limit to anaerobic capacity and it is a function of anaerobic power output. So, if you want to improve anaerobic capacity - you need to train anaerobic power.....does that make sense?
And you train that by not going into fatigue. That's not to say you don't ever train under fatigue but just to make a general distinction.
And, power output depends on muscle fibre recruitment.
We know hybrid fibres, or intermediate fibres can swing both ways - they adapt to the stimuli.
A lower power output favours type 1, higher output type 2 and hybrids sit there waiting for a call - they are plastic and adaptive. To adapt requires a stimulus and recovery time.
If you reduce power output because you are training to exhaustion, the under recovered fast fibres are no longer recruited, burnt out and type 1 are recruited. The adaptive process tends towards type 1....so hybrids migrate towards type 1. If you produce high power under anaerobic conditions and stop when power output drops, the signal, for type 2 fast fibres is....build new mito in type 2....so hybrids migrate towards type 2. Type 2 are fast oxidative....more power....more capacity.
Essentially, S&S here, right..A&A etc?
With no clear cut off point, vague distinctions of fatigue set points, you could argue that medium power targets both. Which is good for general sport applications, right?
Type 2 being fast, oxidative and larger, they also have greater glycogen storage. At higher power, glucose is available on site for anaerobic work via glycogen...it is also then available for aerobic glycolysis on demand which allows that high power work to continue aerobically....upto a point.
And here we have a 400m sprint....fizz through phosphate, fizz through glucose, lactate, slow up at 300m, finish with what you have left via aerobic glycolysis.
Taking no other factors into account...mechanics, skill, leverages...a 400m marks the turning point into endurance....
So now you are able to use glucose quickly, efficiently at high power. That 400m has got a little bit easier because of greater aerobic input towards the end.
Let's take raw speed off the table but stay with a 400m for a bit for a general endurance slant...
Using 400s for intervals at reduced power outputs....
So you get what you train for. In summary, on balance, edging towards lower power output to exhaustion will, if done with adequate recovery, improve markers for better aerobic function with a tendency towards type 1 muscle fibre. Going towards high power non exhaustive will, if done with adequate recovery, improve markers for better aerobic function in type 2 fibres. Going somewhere around medium power will improve markers in both type 1 and type 2. Exactly the adaptation for many sports. Which is informative because that is exactly why 400s are a good distance for training specific adaptations and fatigue management. As a short sprinter now, the reason why I go nowhere near them.
As midfielder playing football as a kid, the reason why I did them, often to exhaustion. Exactly the same the next day, those were the days, eh?
Pavel has said somewhere that a ballsy 400 finisher is a good way to whack up HGH at the end of training. Just one.
Tennis player Andy Murray did exactly that too at the end of a 8 hour practice session. It's all relative.
So descending ladders - fill your boots, if done appropriately attending to your recovery needs. From approx 800 - 400 - 200 - 100 will give you a massive lactate dump and tend towards at best a blend of 1 and 2 fibres but probably edge towards type 1 and certainly improve aerobic function. Other models are available....you could edge towards type 2 by doing 6 sets of 60m, extending distance over time with long rests and no fatigue and do that same interval with more power and not be as knackered. Just saying.
For general broad range energetic capabilities, fill your boots.
Done the way suggested will it improve anaerobic capacity? - in a sense yes but via improved aerobic function.
To actually improve anaerobic capacity you should rarely train to exhaustion instead train anaerobic power output by targeting high powered fast oxidative muscle fibres.
Why? Because building fast oxidative fibres increases mitochondria in those fibres and in hybrids = more phosphate, more glycogen = more anaerobic power = more aerobic power = more power endurance. (Other factors contribute obviously but just on energetics).
You get to choose which way you want to go then, right? You get to do what you like to do or favour for a sport or pastime.
The time efficient argument - not sure it holds really. A short knackering session, 4 days recovery. 2 days of tempo running instead, 2 days off, a mild lactate stimuli, practice running gait, technique and breathing etc....splitting hairs, toss a coin. Outside of just running though and for rugby, football etc, interval training probably wins for a more general crossover. If a runner, tempo probably gets it but not if you are falling about, arms flapping, head down, breaking at the waist, knackered, heel striking, in pain, sucking gels, farting sugar and in a mess.
All caveated by population and variables mentioned at the start.