[rojeee]

Depends what you want to do. Run a fast 5k? Improve aerobic system? Something else? Short fast bursts of running will improve your anearobic capacity. Slightly longer intervals run a bit slower may target your lactate threshold and lactate clearance rates. Slower running for longer distances will target your aerobic system.

As people, and the featured article, notes, short intense intervals may burn the most calories but I would argue for more well rounded fitness you need to do a bit of everything.

Due to HIIT, there's loads of people around the world now who have great anearobic metabolism but non-existant aerobic metabolism. The effects are increased autonomic stress from all the anearobic work and an inability to exercise for long durations without quite a lot of stress on your body.

[scp3125]

That... doesn't sound like HIIT. HIIT shouldn't average out to anaerobic heart rate ranges, otherwise you really lose the benefit of keeping your heart engaged in aerobic ranges during the rests. And to be honest, HIIT used for recreation shouldn't even peak in the elevated ranges above 167 bpm, if you're talking about doing it safely over years for health. Higher than that might be effective in training to increase aerobic capacity or lower your overall heart rate, but may damage your heart over time.

The effect of taking those controls on HIIT should result in reducing the autonomic stress response of /all/ exercise on heart rate, not increasing it. The demonstrated effect of HIIT is being able to efficiently scale aerobic capacity without increasing the time required and prolonged physical stress on the body. That's why Olympic athletes have been using interval training for a century, and from the 90s to this day, have used HIIT techniques like Tabata to increase their overall ability to exercise for a long duration, without having to actually commit to exercising for repeated long durations.

I'm not sure where you got that piece of information about loads of people with great anaerobic "metabolism" vs aerobic "metabolism". It would truly be very difficult, but not impossible to consistently raise your anaerobic capacity, (which I'm guessing is the implied relation to processing lactic acid efficiently as a fuel source for exercise?) but not raise your aerobic capacity also. Most of the ways I have seen that involve some kind of ketosis, or something that would otherwise deprive the body of the baseline glucose to drive aerobic capacity up in tandem with anaerobic capacity (because there's just not available excess glucose to store as glycogen in muscles beyond basal mechanical muscle operation and may lead to atrophy from burning muscle as a fuel source a.k.a. awful orange piss). And generally you would have a hard time building up extra muscle in that state as well, so it would be generally not advisable/possibly extremely dangerous to do so without proper diet and nutrition.

disclaimer - I am not an exercise physiologist or certified in any way. I'm an idiot on the internet, so please feel free to correct me if I'm wrong or don't have it quite right

[rojeee]

My point is that if the capability of your aerobic system is very poor - and it is for the vast majority of people, including many HIIT advocates - then whatever exercise you do, you'll very quickly be approaching anearobic territory and find it very difficult to stay at a metabolic steady state for long durations of exercise. When I mean anaerobic, I don't mean "zone 5". I just mean that there will be a much higher percentage of anaerobic glycolysis happening than perhaps should be for a particular level of exertion.

For these people, their aerobic system is so bad that they need to walk to stay in "zone 2". It stands to reason that if they are doing a HIIT session then they are very quickly in the territory of zones 3 and 4, so we are looking at lactate threshold or critical power levels of exertion. So you are looking at more than 60-70% of power coming from anaerobic metabolism. That puts a lot of stress on the body.

For these people to develop their aerobic systems, they need to do a lot of slow jogging or fast walking. Eventually if they do that enough then they'll be much healthier, find HIIT sessions easier and recover much faster. People that spend too much time doing intense exercise will eventually end up with some degree of autonominc dysfunction. I've seen it plenty of times with HIIT people that want to start doing running. They train multiple times a week. Look stressed and knackered. Think they are aerobically fit but can't run a 5km in less than 20 minutes and can't run a 10km at all.

I do HIIT all the time, e.g. 20x400m on the track with 3min walking recovery. But as you noted, one doesn't do these sessions to increase ability to exercise for a long duration, you do long runs e.g. 25km at aerobic threshold for that. I don't do these sessions to primarily target adaptions to my aerobic system either. Instead, I do HIIT sessions like 20x400m with varying levels of recovery to target different apations. E.g. with long recovery I can target anearobic capacity. With shorter recoveries and a lower amount of reps, I can improve lactate buffering and usage.

Finally, it's reasonably well known in athletics circles that if you improve your lcatate threshold, i.e. increase the intensity that you are able to stay sustainably aerobic, then you end up decreasing your anaerobic capcity. The reason why is that the lactate threshold training reduces your ability to produce lactate.

Source: I've been running a long time and have coached runners of various levels.

[tylerhou]

Think they are aerobically fit but can't run a 5km in less than 20 minutes and can't run a 10km at all.

Is this a typo / did you mean 30 minutes? 5k in 20 minutes is already maybe top 2% of people who compete in races. And running a 10k is far, far easier than running a 5k sub 20.

[rojeee]

Yes, sorry, you are right to point that out. I meant 30 mins!

[scp3125]

So the data nerd in me is struggling with your framing a bit. HIIT for people with "aerobically poor systems" may resemble slow jogging or fast walking based on HR alone. Also outside of analyzing blood serum or glucose monitors, there isn't much of a reliable way to secondarily analyze the lactate threshold (actually). There are metabolite analysis that can be done, or things like creatine supplementation to facilitate the "smooth" transfer between aerobic and anaerobic processes, but on a fundamental level, my understanding as a lay person, is aerobic exercise produces lactic acid as a byproduct, and anaerobic exercise uses lactic acid as a fuel source. That is the reason anaerobic capacity decreases, as your lactate threshold increases. The real reason you are subject to a much greater degree of boom-bust is "lactate threshold training" is about increasing the physiological load the body is capable of sustained aerobic capacity for exercise (which is what you're saying), primarily by training your body to increase the amount of available glycogen. That's really only useful in the context of running and a few other endurance sports, and is hardly a metric of overall health.

Also IIRC the story of Marathon was relevant because the runner died to deliver the message. That sort of implies, despite the feat, that not everyone should be able to do that, nor should they.

HIIT conceptually depends on what your body does in a given state, not a unit of exercise. I would wager large sums of money the people that are overeager to engage with higher and higher intensities are not actually looking or reading the metrics of their own bodies, and adapting the behavior accordingly. It's not really about want or "determination" lol, it's about what you do to get your heart rate in a given place, and the fluctuations that produce an effect, given the systems in your body.

You kinda strawman these "HIIT people", as if they're actually doing HIIT, or as if they represent everyone. Autonomic dysfunction, based on overtraining syndrome or overexertion is not the same thing as observing a HIIT protocol based on your own biometrics. It's honestly hilarious, because HIIT and interval training at large is specifically designed to avoid OTS, especially where it relates to the serious damage that can occur to the vascular system, musculature, and ligaments, once scaling up the duration with a similar level of intensity occurs. Running a 5km in less than 20 minutes is a perfect example of a not very good metric actually. There are plenty of people that could put themselves at risk of damaging themselves to do such a jaunt. It is a very light entry point, but arguably is a good metric for elaborating on why training is important to be able to accomplish physical feats safely, but there's kind of a packaged Ableism in your argument that I kind of find distasteful. If your doctor looks at blood serum, analyze heart rates under stress loads, and examines blood oxygen under stress and during sleep, you can pretty much guarantee they will arrive at some degree of analysis that could prove (outside exception of health conditions or illness) a degree of general health and fitness.

I understand running is important to you, personally and culturally. Don't attack tools in the toolbox of fitness, just because you see other people using them wrong (edit: you did say you do use it). Everything in the world is a nail if you're holding a hammer, etc etc.

Conceptually, most of what you said is sound, but yeah. I think you're a nerd for process, which is cool, making kind of misguided arguments that are not really about what we're talking about here, which is why the article observes a principle experimentally we've known works for over a century. Also I personally like HIIT, interval training, and HIRT especially for all of the reasons I've described. :)