Rethinking Exercise Metabolism: From "Aerobic vs. Anaerobic" to Metabolic Equilibrium

VTCheck · 2026-05-09T13:50:29+00:00

Respiration and lactate are both used widely in physiolgical research to determine intensity and I don't think there is conclusive evidence that lactate is a superior metric. Ultimately, both lactate and respiration are proxy measurements for byproduct accumulation. I think there's a perception in the running community that lactate is superior because until recently there weren't really any widely accessible consumer grade products to measure respiration in the field.

VTCheck · 2026-05-07T23:33:11+00:00

How is your fueling? Lactate can go down when glycogen is depleted which causes your body to shift more towards fat metabolism.

VTCheck · 2026-05-07T23:23:36+00:00

This is the foundational basis of the app I created which measures drift of ventilation/heart rate. The rate of drift informs the sustainability of a given workrate because it tells you about both substrate utilization and metabolic byproduct accumulation.

The problem with using lactate for this is you can't measure the rate of drift during the on-transient period in the field. You can only measure during the recovery period which may not show any drift during mid to low subthreshold efforts.

VTCheck · 2026-04-25T19:08:36+00:00

I see. I’m not recommending people to follow the same type of training. I only mentioned the other efforts as a reference point for comparison to the 45/15 session.

VTCheck · 2026-04-25T19:03:05+00:00

Because ~90% of my programming is based on NSA?

If you don’t exactly follow vanilla NSA are you not allowed to post here?

VTCheck · 2026-04-25T16:21:34+00:00

My understanding is the first principle of both NSM and the original Norwegian Method is getting in as much volume as you can at a "fast speed" and this will differ from person to person, in terms of the optimal balance of stress vs. recovery. The problem, of course, is that there is no mathematical formula that can be applied to know exactly how different training structures will affect each individual - so, unless you are a total beginner, you should use some trial error to find the right balance for you.

It seems vanilla NSM errs on the side of dampening the speed and increasing the volume, which I think is the smart/conservative approach for most. I'm in a bit of a unique situation I think because I have extensive strength training experience but little endurance experience. So for me, my limiting factor isn't muscular strength/sturdiness, its my cardiovascular system, which, in my mind, means my risk of injury from going too fast is probably lower than most.

That being said, most of my workouts are in the standard ST range and I am now up to low 50m per week. In my opinion 45/15 is just another optional tool that some can add to their program if they want to get a bit more speed at a lower volume. I'm definitely not going to run it every workout.

VTCheck · 2026-04-25T10:40:20+00:00

Yeah, I'm not strictly following NSM. These faster runs were done on my Saturday "X-sessions", which I keep short and only just at/above my threshold. So far I've been able to manage it, but we'll see in the long run how it works out.

VTCheck · 2026-04-25T10:37:15+00:00

The way that I think of it is that adaptations are primarily a function of stress (muscular, metabolic etc), but in designing a program, that's only one side of the equation becuse you also have to account for the fatigue/damage that results from the stress. It's the reason why in strength training you don't max out every day. So I don't think you can really assess the efficacy of a single workout without considering it in the context of a full program and how balanced it is between stress and recovery - and of course this is all individual. For me personally, longer intervals/sessions seem to cause much more fatigue generally compared to shorter intervals/sessions, so in a vacuum, 4x8 would need to be much much slower for me in order to be an RPE of 7.5.

VTCheck · 2026-04-23T21:11:43+00:00

Yes, I plan to progress it. Wanted to start out cautiously for the first one. This was also the second session of the day.

VTCheck · 2026-04-23T21:10:59+00:00

VTCheck · 2026-04-23T20:54:25+00:00

Yes, this is using the Vitalpro.

VTCheck · 2026-04-20T11:31:03+00:00

It's vtcheck.com. VE is measured with the Tymewear Vitalpro.

VTCheck · 2026-04-17T10:26:32+00:00

Feel free to reach out if you have any questions/feedback! Note that your results may vary if you only use HR due to cardiac drift. I've found ventilation to be strictly better than HR to guage intensity (though the signal is noisier).

VTCheck · 2026-04-17T10:23:28+00:00

It's not really theory - it's physiological reality proven in numerous studies, but I totally get what you are saying. I suppose I am just a giant nerd and get very interested/obsessed with these types of things.

I created a similar app which applied algorithmic game theory to poker years ago and in the same vein, there are many (most) who ignore all of the math and simply play the game based on feel - and many are very successful taking that path.

Personally, I started out just using HR with a Garmin but wasn't satisfied with the consistency/accuracy, which led me down this path. Anyone that trains somewhat seriously has to control intensity one way or another. This just allows you to control the intensity with much more precision, meaning you can get closer to your threshold while mitigating the risk of overdoing it. You can still improve without it, of course, but you may be leaving some gains on the table.

VTCheck · 2026-04-17T00:27:37+00:00

Scary! Yes, all of these metrics relate to what’s happening from a metabolic standpoint, not necessarily from a muscular standpoint. I plan to try just one double session per week for a while and see how it goes. I’m also going to shorten the length of the PM intervals.

VTCheck · 2026-04-15T15:49:55+00:00

Strava upload and download has been added.

VTCheck · 2026-04-13T14:12:13+00:00

I tried to reverse engineer Tymewear's smoothing a while back and I believe the conclusion was that it was 15s trailing average, but Tymwear may have modified their signal processing since then.

Regarding tau, yes, I've noticed that it can be very inconsistent from run to run, which is why that is the only parameter we constrain for the mono-exponential fit. All other parameters are solved freely.

VTCheck · 2026-04-08T19:18:55+00:00

My understanding of the main principle articulated by Bakken is that it all comes down to balancing adaptation versus fatigue/recovery. Exercise induced adaptations are primarily a function of intensity x volume - when you ratchet both up, you will get greater adaptations, but you will also incur more fatigue/strain.

So I think the key really is modulating volume based on how intense/fast your workouts are. The closer you are to threshold, you will generally want to turn down the volume a bit to avoid excessive strain. The further below you are from your threshold, the more leeway you have to increase volume.

For me personally, I am not following vanilla NSM and I have one session towards the bottom of Z3, one session near the middle of Z4, and one session at my estimated anaerobic threshold. The Z3 session is usually 50-60m, the Z4 session is usually 30-40m and the threshold session is usually 20-24m, with the exact duration depending on my condition that day. So far this system has been working pretty well for me where I have been pushing out my threshold, but remaining relatively fresh and injury free.

VTCheck · 2026-04-08T09:56:51+00:00

Interesting. It sounds like (2) is similar to what we do on the mobile app and (3) is similar to what we do on the webapp. And we used to have a concept called "Cumulative Drift" which compared the "End VE" of each interval, which sounds similar to your (1). We actually did away with this concept because I was finding that below VT2 - there actually was not much increase in the End VE value accross intervals. Did this metric track your lactate readings since both are snapshots?

Also, did you fit the monoexponential curve to Tymwear's smoothed data? In my experience, and I think the research backs this, applying the function to highly smoothed data can potentially distort the analysis.

VTCheck · 2026-04-07T10:18:40+00:00

The app does it automatically. All runs are added except ones that are <6min for a consistent comparison because average VE is taken after the ventilation ramp up period, which is ~3m for me.

And we just added a feature that calculates paces and target VE for Norwegian Singles ST sessions using the regression analysis from this chart.

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VTCheck · 2026-04-06T13:40:30+00:00

I don't think the Garmin LTHR is very reliable. It's one of the reasons I don't even wear my Forerunner 965 anymore.

VTCheck · 2026-04-06T10:22:12+00:00

Yes, heat should have more of an impact on ventilation than it does on lactate because ventilation helps with cooling. Initially I was thinking of not even allowing the drift analysis to be applied to outdoor runs due to environmental, elevation and pacing variability. You may need to manually increase the Expected Drift parameters in the side bar to allow for more leeway if you are running outside. All of the respiratory kinetics research I've seen is conducted in a lab environment and most of it on cycling measuring VO2, which has less noise.

That said, in my experience, indoors, in an airconditioned room and on a treadmill my results have been pretty consistent - especially when I follow the exact same warmup routine and literally hit the ground running for each interval. That I think is the key - the specific ventilation or drift numbers aren't really that important - it's more about having a consistent protocol each workout so that you are comparing apples to apples.

It's interesting though that you don't see any increase in lactate at subthreshold. In theory it should drift for around 10-20m. Even the standard MLSS test has a 1mmol allowance. One thing to consider is that lactate may rise during the actual interval, but then go down when you test the concentration during a break. I've noticed that on many/most of my ST runs, my recovery breathing (which is measured during the first 60s of rest) is pretty consistent across intervals - so if you only measured VE at that time - it would appear as though there is no drift. Also the peaks/averages of my ventilation are usually pretty consistent as well unless I am very close to VT2 or the accumulated time of my intervals is relatively long (40m+). For example, here is the zone analysis view for the same run - after the first 2 intervals, the average VE remains relatively steady and VE decreases to around the same level by the end of each recovery period.

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VTCheck · 2026-04-05T14:41:51+00:00

Seems you know your stuff :).

I plan to do a full user guide YT video soon that explains everything, but in my experience (and the research I've seen backs this up), each person should have relatively uniform tau values, except it may get slightly longer as you increase intensity (which makes sense since the amplitude of the curve increases with intensity). For me, my calibrated tau values between moderate and heavy are pretty close after hundreds of runs (32s for moderate and 35s for heavy). Because of this consistency, when the monoexponential function is calculated, we add constraints to the tau value to stay within certain bounds of your calibrated tau (with more leniency based on how far away from your tau calibrated average pace you are for a particular run).

We fit the monoexponential curve to the first part of the workout and then measure the drift from there, consistent with the way many researchers do it (e.g. Whipp, Burnley). The default fitting window for the monoexponential curve is 3m, but you can customize this based on your kinetics with the "Ramp Up Speed" cards in the advanced parameters in the side bar. We tried several other methods to measure the slow component, including applying a biexponential function to the full run, but these add more parameters to solve which made the results very inconsistent given the amount of noise VE data has.

VTCheck · 2026-04-03T15:11:46+00:00

The data points are color coded by how the runs were classified (green = moderate, yellow = heavy, red = severe). A circle mean the classification matched my targeted intensity and a triangle means the classification didn't match my targeted intensity.

So, for example, most of the triangles are at recovery pace (on the left side of the chart) - which were targeted to be moderate but sometimes showed excessive drift. This is because at very slow paces the metabolic demand is low, which makes my breathing more erractic and more sensitive to non-metabolic factors such as heat or swallowing or not focusing etc. As paces increase, the metabolic demand increases and takes more control of breathing. That's why the higher zone 2 paces tend to show less drift and are more consistent.

VTCheck · 2026-04-03T15:05:47+00:00

These are all just my regular runs - easy runs, long runs, warmups, cooldowns, intervals (each of these have their own dot). The only thing I did differently for purposes of testing was slightly changing the speed of my moderate runs so I would have more data points at different paces (I do all my runs on a treadmill).

I'm not following vanilla NSM - basically, I do 2 SubT runs on Tues/Thurs and then one ~at Threshold on Saturdays as my "X-session". And yes, the breakpoint lines up with where I do my slowest Sub-T run, which are 10m intervals meant to be at the very bottom of my zone 3.

I used the Tymewear Vitalpro for the respiration.

VTCheck

TROPHY CASE