Why call Anaerobic , if we never get a point w/o O2?

I´m always confuse when you guys said/talk about anaerobic - my understanding is about how much % of O2 is in muscle. As far as i know even a 100m Sprinter dont get below 10% of O2 (even called a anaerobic activity) - They just utilized O2 in a faster rate , give a Quick drop in O2 but never get w/o O2

So everytime i get confused when said anaerobic training (w/o oxygen), what really means if non training is anaerobic or w/o O2 in a muscle.

Could you please guys elaborate

1 Like

There are pathways that produce atp without using oxygen even in the presence of oxygen. I’ve seen it described and prefer to think of it as non-aerobic energy production.

Glycolysis => Krebs cycle => a&b. This all happens without using oxygen.

a. If there is sufficient oxygen the Krebs cycle’s electron carrier products will follow the electron transport chain and deliver electrons to oxygen producing way more atp.

B. If there isn’t enough oxygen to accept those electrons another anaerobic process, fermentation, takes up the electrons. This causes the decrease in ph (acidification) and the byproduct lactate.

We always have both aerobic and anaerobic processes happening. You can’t really have aerobic metabolism without anaerobic processes.

1 Like

Thanks for you answer. I dont get or dont make me understand.

The question is: Training and the muscle NEVER is without oxygen in the muscle. So basic NONE type of training is Anaerobic.

Why called some training anaerobic and others aerobic , every training has oxygen in the muscle , when decrease too much you stop! or died :grinning: ; but never is without oxygen.

I’d suggest ‘anaerobic exercise’ is like acknowledging the addition of anaerobic metabolic processes on top of continued aerobic processes. You’re right. Biological tissue doesn’t like anoxic conditions. Like @hammervalley said, it’s more referring that anaerobic metabolic processes are contributing a net addition to the work output (power/speed). ie. not all of the external mechanical work can be attributed to aerobic energy expenditure (oxidative phosphorylation).

It’s definitely an imprecise literal use of the term, but at this point it’s pretty commonly understood. Hope that helps!

Hi @Susigan, and thanks for your question! This can be a tricky one, and like @hammervalley and @SpareCycles said, it’s more about the processes that produce energy.

The anaerobic process occurs within the cytoplasm of the cell. This is used to help power the muscles when they are contracting by breaking down and resynthesizing ATP. The aerobic process occurs in the mitochondrion, which is separated from the cytoplasm of the cell. These work together to derive energy via the appropriate pathway based on the energy needs for muscular contraction. So like you said in your original post, the 100m sprinter will never really be without oxygen. In a 100m sprint, the energy requirements are so high for that short time, that glucose is the primary energy reserve we will tap into as this can be broken down quickly to generate ATP to power muscle contraction. We will also tap into phosphocreatine stores, but let’s leave that alone for now.

Because we need to generate a lot of ATP for this 100m sprint, the slower aerobic process will be unable to keep up with the demand for removal of H+ and electrons, but it will be active. Something called substrate level phosphorylation will be a big driver of ATP resynthesis during that sprint, and because of the rapid accumulation of H+ and e- (and the aerobic system being unable to transport all of them to the mitochondria), pyruvate (an end product of glycolysis) will accept them and convert to lactate. That substrate level phosphorylation is the strong driver of anaerobic metabolism, and hence why there is confusion with that terminology and those terms are sometimes used inaccurately to describe what is happening. See the chart below (reference below that). It’s a nice table from a study that estimated anaerobic and aerobic metabolic contributions to 100m sprinting. You’ll see there is a high aerobic component as well.

When we talk about “anaerobic” training, it’s more referring to the primary system we’re trying to train, so that might look very similar to sprint-type training, or the 100m dash you are referring to. There is still an aerobic component, but when applying this to training, we’re usually talking about the dominant energy system.

Duffield, R & Dawson, B & Goodman, C. (2004). Energy system contribution to 100-m and 200-m track running events. Journal of science and medicine in sport / Sports Medicine Australia. 7. 302-13. 10.1016/S1440-2440(04)80025-2.


Thanks for response @ryan @SpareCycles @hammervalley

I based my question in in contemporary model of bioenergetics, where these events u describe, phosphogen, glycolytic, and oxidative pathways that all of them are overlapping, and the time frame is 0 to 100 milliseconds

So a 100m sprinter will not stop because running out of Pcr or creatine phoysphate. its because the levels of O2

the oxidative and non-oxidative ‘energy systems’ all work to bolster PCr and ATP levels between muscle contractions. If we break down the 0-100 millisecond time window listed what we have is

  1. Within 0-15 msec of muscle contraction PCr is broken down to resynthesize ATP to fuel contractions

  2. Within 15-100 msec PCr is resynthesized from glycogen breakdown and glycolysis (ATP from glycogen breakdown and glycolysis restore PCR)

  3. Glycogen lost during #2 is resynthesized during relaxation period (Resynthesis of glycogen from ATP produced by lactate oxidation)

This model is referred to as the glycogen shunt, and it’s physiological function is to provide a rapid release of energy needed to support muscle contractions on an order of 20-100 msec. The conventional view of energetics is that PCr supplies all the energy for short bursts of 10 seconds or less, but that is not supported by experimental research.

The oxidative and PCr systems are entangled with one another, meaning that reoxygenation and de-oxygenation are closed linked to rates of PCr depletion / repletion
(1,2). This is contrary to the outdated model where PCr is utilized first prior to the
initiation of oxygen consumption. However, when we pair max strength with high
energetic demand ‘aerobic’ work (dubious term) these rates may uncouple from oneanother. This is partly due FT fibers being poor when it comes to oxidation,

  1. McCully, K.K., Lotti, S., Kendrick, K., Wang, Z., Posner, J.D., Leigh, J., et al.
    “Simultaneous in vivo measurements of HbO2 saturation and PCr kinetics after
    exercise in normal humans.” Journal of Applied Physiology.
  2. Shulman RG, Rothman DL. The “glycogen shunt” in exercising muscle: A role for
    glycogen in muscle energetics and fatigue. Proc Natl Acad Sci U S A

So we are creating this aerobic/anaerobic training , will be more produtive if we create based on how the athelete deal with oxygen delivery ouldn’t it be better to create the training and intervals for the athletes or instead of thinking that he needs more aerobic or anaerobic training, and to separate the training based on that?

Of course, I believe that great coaches like you, and with experience, know and have the feeling to give something that the athlete needs and manages to adapt.

1 Like

I’m not quite sure how to put an answer together for your point broadly, because - and please take this as constructive criticism - I feel like you might be overcomplicating one side of the question, and oversimplifying the other side. But you’re definitely hitting on some really interesting areas of bioenergetics, so let’s see if I can add to the discussion. Let’s start by overcomplicating, then finish by oversimplifying! Afterall, there is always more nuance :nerd_face:

You are totally correct that the ‘old model’ of energy provision being ‘exclusively’ one thing or another is outdated. All systems (ATP-PCr, glycolysis, OXPHOS) are always working together.

A 100m sprinter will have to slow down (but not stop*) when they have neither enough PCr nor enough O2 to meet the energy demands of locomotion at their desired work rate. You’re right, this is primarily due to a limitation to DO2 (O2 delivery) as the rate-limiting step to PCr resynthesis. But the demand is so much higher than what O2 can possibly provide, it is the PCr that acts as the functional limiter to performance in this example.

To think about it another way: training to improve a 100m sprinter’s VO2max is probably far less productive than training their ‘anaerobic capacity’ (handwavy term which includes a lot more than just PCr, but for which net PCr depletion rate is probably as good a proxy as any). I’ll touch on this again at the end.

*Task failure’ constitutes not being able to meet the energy demands to sustain the external work rate, but the options are not binary either 1) continue, or 0) stop. The athlete will just have to involuntarily slow down until metabolic energy production rate (net of aerobic + anaerobic) is able to match external work rate. Task failure will constitute stopping completely in a contrived activity like an incremental ramp test, where the nature of the task does not allow for slowing down.

Continued from above, during continuous exercise above Threshold (FTP/CP/MLSS/whatever you want to call it) in the severe intensity domain, PCr cannot be net* reconstituted, no matter the rate of aerobic energy provision. By definition, because severe domain work rate exceeds the maximal rate of “wholly oxidative energy provision”, which is CP.

Severe domain exercise will continuously deplete ATP, PCr, and other substrate resources, and accumulate ADP, Pi, H+, lactate, and other metabolites. Meanwhile mVO2 (muscle O2 uptake) will continuously increase toward mVO2max, through trying to meet the ongoing energy demands of both A) locomotion, and B) restoring that metabolic milieu, while C) that disturbed milieu progressively decreases contractile and mitochondrial efficiency, therefore mVO2 is driven toward mVO2max, which contributes significantly toward the body reaching systemic/pulmonary VO2max and task failure.

*‘net’ because there might be fiber-specific reconstitution going from higher workload where more fibers are activated, to lower workload, where fewer fibers are activated, but both within severe domain. I’m not sure if this has been investigated. But exercise to failure within severe or extreme domains will almost by definition (there may be some exceptions around the margins of the intensity zone) deplete PCr to a physiological minimum which will not literally be zero, while simultaneously reaching mVO2max and VO2max.

Yes, part of this relationship is called the ‘phosphocreatine shuttle’, which describes how PCr is used as an intermediate transport molecule for energy alongside ATP, between mitochondria (energy production from combustion of CHO/fat & O2) and contractile elements (energy consumption to produce mechanical work). So talking about ‘PCr depletion’ or ‘reconstitution’ is really just describing the net change - the flux - in PCr.

Alongside the PCr shuttle there is also free ATP moving directly-ish from mitochondria to contractile elements going toward locomotion. Hence the double-demand for energy, as mentioned above.


Ok, let’s see if I can oversimplify now!

All that being said, I would argue it’s totally acceptable from a functional and ‘common language’ perspective to talk about ‘aerobic and anaerobic training’. Like @ryan said, it’s more like an intention to prioritize training toward improving one system or the other, depending on which system has a more important contribution to the demands of the target event, and knowing that both systems are always working together.

There are certainly training methods that will prioritize one over the other, and in my opinion the trade-off is (typically? always? often?) zero-sum: choosing to prioritize one may inhibit or diminish the other. ie. in the case of the 100m sprinter, they may (may) perform worse through training their max aerobic capacity, if there is a compensatory trade-off in anaerobic capacity.

The question of which energy system is the predominant limiter to performance is another great question that depends on the demands of the event, and the athlete’s relative physiological strengths and limiters to meeting those demands. So I don’t think we need to dive into the biochemistry (although I love doing so!) to understand at a functional level A) the athlete’s current capabilities, B) the demands of the task, and C) the training methods that will best get the athlete from A to B.

Some papers that might be of interest:

That was fun! Thanks for stimulating some deeper thinking on the topic!


I’ve just incidentally come across this 2015 opinion article arguing in favour of your position @Susigan, and I can absolutely appreciate that side of the debate. It’s freely available. Very worth the brief read.

Imprecise language is literally the worst, so maybe I should play devil’s advocate and come around to your side, and we can all start using more precise terminology :slight_smile:

1 Like

Thanks for you response @SpareCycles i really aprecciated.

i don’t argue against biology :slight_smile: But on a limiter of performance is because the demand of a metabolic energy production rate - On A Critical Power related and the limiter in performance; W’ was initially described as an anaerobic work capacity but has subsequently been shown to be associated with the depletion of intramuscular energy stores is sensitive to alterations in oxygen delivery

[(The work capacity of a synergic muscular group)]

Influence of hyperoxia on muscle metabolic responses and the power-duration relationship during severe-intensity exercise in humans: a 31P magnetic resonance spectroscopy study

1 Like

Sweet topic

The sprinter will stop when 100 m is finished

But the sprinter will slow down because decreased PCR levels decrease the maximum force and therefore power production and therefore speed

1 Like