As we know, the aerobic process doesn't function well with ME, so it's best to use the anaerobic process as much as possible.
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But what about lactic acid ? Where does it fit between the aerobic and anaerobic energy paths ? Does it happen in the aerobic pathway too ?
The short answer to your question is no, lactic acid is not created by aerobic energy production, only by anaerobic energy production. The long answer, which explains why, is as follows:
In human beings, when we use sugar for energy, there is a two-stage process that extracts the energy contained in sugar.
The first stage of the process is called glycolysis, and this occurs outside of the mitochondria; glycolysis is a separate system of energy production in the cell, that can if necessary function independently of the mitochondria in the cell.
The second stage of energy extraction from sugar occurs within the mitochondria.
Basically, glycolysis extracts a portion of the energy in the sugar, and then typically passes the job on to the mitochondria, which extracts the remaining energy from the sugar. That's the two stage process, with both glycolysis and the mitochondria working together in a sort of production line to produce energy.
In this two stage production line process, as glycolysis extracts energy from the sugar, it converts the sugar into pyruvate (and does not need oxygen to do this). The pyruvate created by the glycolysis process still contains further energy, and is passed on to the mitochondria in order to extract this energy; once the pyruvate enters the mitochondria, it is burnt with oxygen (aerobic process), which extracts the energy pyruvate contains. So that's the two stage process.
But if there are any blockages in the mitochondria (as studies have shown may exist in ME/CFS), then the handover of pyruvate from glycolysis to the mitochondria may not occur. Then instead, the pyruvate needs to be got rid of, and so is converted into lactic acid, and this lactic acid waste product is flushed out of the cell and into the blood (where ultimately the liver deals with it).
So in ME/CFS, this is probably how excess lactic acid arises: when the blocked mitochondria are unable to accept the pyruvate created by the glycolysis process.
When the pyruvate is not passed on to the mitochondria, and instead gets converted to lactic acid, this is termed
anaerobic glycolysis, because no oxygen is involved. By contrast, when the pyruvate from glycolysis is passed on to the mitochondria, this is termed
aerobic glycolysis, because in the mitochondria, oxygen is used to burn the pyruvate and extract the energy pyruvate contains.
Aerobic glycolysis produces energy more efficiently than anaerobic glycolysis, and aerobic glycolysis does not create the problematic lactic acid waste product that anaerobic glycolysis produces.
However, even in healthy people and athletes, you will get a degree of anaerobic glycolysis going on. This is because on a short term basis, in the first few minutes of vigorous exercise, anaerobic glycolysis can supply energy faster (it has a high power output) than aerobic glycolysis (which has a lower power output).
This is the one main advantage of anaerobic glycolysis: it has a high power output, and can supply energy faster than aerobic glycolysis can.
Though the high power output capabilities of anaerobic glycolysis quickly expire and exhaust themselves after 1 to 3 minutes of vigorous exercise, as a result of the lactic acid build up, and then in healthy people, they fall back on the aerobic glycolysis for energy (which utilizes the mitochondria and oxygen). Aerobic glycolysis can operate and supply energy for hours.
Because of its high power output, anaerobic glycolysis is also called fast glycolysis; and because of its lower power output, anaerobic glycolysis is termed called slow glycolysis.
Some athletes will specifically train certain parts of their energy metabolism, depending on their sport. For example, if the sport you compete in is a short duration exercise lasting only 1 or 2 minutes (eg, 400 m or 800 m sprints), then you'd really want to train your anaerobic glycolysis system (fast glycolysis), as this is where you will be getting most of your energy from.
To target and athletically train your anaerobic glycolysis energy system, you generally perform very short bouts of exercise, lasting no longer than say 60 to 90 seconds, and then take a rest for 5 to 10 minutes. That way, you engage the anaerobic glycolysis system, but not the aerobic glycolysis system, because the latter only really comes into play after the first 1 to 3 minutes of exercise is complete.
Anaerobic glycolysis and aerobic glycolysis are 2 out of the 4 energy systems that you use during exercise.
A good overview on these 4 different energy systems, and how to train each one, is given in
this article.
It has occurred to me that ME/CFS patients
might benefit from exercise training that specifically targets the anaerobic glycolysis energy system (which as explained above, involves short bouts of exercise no longer than 60 to 90 seconds, followed by 5 or 10 minutes rest). In ME/CFS, as
@Dechi mentions, the anaerobic glycolysis system is probably working fine; it is the aerobic glycolysis system that is likely blocked.
So it is possible that exercise which only targets and engages the fully functioning anaerobic glycolysis system may not cause ill effects; and by training this particular anaerobic glycolysis system, you might in principle be able to raise your PEM threshold.
On the other hand, such targeted exercise may be just as bad for ME/CFS patients as regular exercise, so I think one would need to be very cautious about trying any anaerobic glycolysis training. We don't know enough about ME/CFS to be certain about what causes PEM.
Lactic acid, though, is not the only factor thought to contribute to PEM. If you read about the
Myhill, Booth and McLaren-Howard Theory of PEM, lactic acid is just part of the PEM picture. But according to their theory, the main factor causing PEM is the temporary physical loss of ATP molecules that they propose occurs when ME/CFS patients exercise.
You may also be interested in some of the "PEM Buster" supplements detailed in
this thread. Many of these likely work by reducing exercise-induced lactic acid.