Exercise Intolerance vs. PEM/Exertion Intolerance

Pyrrhus

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Exercise Intolerance vs. Exertion Intolerance vs. Post-Exertional Malaise

A common source of confusion are the terms "exercise intolerance" and "exertion intolerance", and how they relate to PEM. So here's a brief clarification:
  • Exercise Intolerance is a medical term that refers to the inability to perform aerobic exercise. Even though the patient is trying their best to exercise aerobically, a physiological problem is depriving the exercising muscles of sufficient oxygen, resulting in rapid muscle weakness/soreness.
  • Exertion Intolerance, on the other hand, is a general term that can refer to any bad reaction to any type of exertion, physical or cognitive.
  • Post-Exertional Malaise (PEM), also known as Post-Exertional Symptom Exacerbation (PESE), is a type of exertion intolerance where there is an exacerbation of symptoms (and maybe some new symptoms) after minimal exertion.
Hope this helps!
 

Pyrrhus

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but couldn't BOTH exist in some of us?
Yes, ME often involves both PEM (exertion intolerance) and Exercise Intolerance (due to dysautonomia).

For more on the Exercise Intolerance, see:

Insights from Invasive Cardiopulmonary Exercise Testing of Patients with ME/CFS (Joseph et al., 2021)​

For more on the PEM (exertion intolerance), see:

Post-Exertional Malaise, Fatigue, and Crashes
 
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borko2100

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I've always wondered how different people experience "Exercise Intolerance". I think it is safe to say almost everyone with ME experiences it, but how they do probably differs from person to person.

I think there are several possibilities:

- general symptoms, such as dizziness, nausea, etc.
- rapid fatiguability / premature cardiovascular and muscular failure - muscle pains, being out of breath, etc.
- both of the above
- none of the above, but delayed PEM as a reaction to the exercise.

I wonder which one is the most common.
 
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Heaviness taking over....
Air hungar- in the lungs but the whole body is reporting on it
You look at the coffee you might normally want to have, and the idea of being more alert sounds awful.
No coffee today.
The eyes are meanwhile reporting on the autoimmune issues with whole ditty...every day my eyes have differing issues to report on- eyes pouring today
Digestion is going off; energy disappeared in the gut.....leakage is starting up worse

etcetera
 

Pyrrhus

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@Pyrrhus How is atrial fibrillation triggered by exercise intolerance?
Great question, although you open a can of worms by mentioning atrial fibrillation. I am not in any position to give a definitive answer, so I'll simply make a few points:
  • The aerobic exercise intolerance observed in ME is due to dysautonomia of the autonomic nerves that control blood vessels. (the nerves that terminate in the endothelial layer of blood vessels)
  • Atrial fibrillation, from what I can tell, may be due to dysautonomia of the autonomic nerve that controls the heart rhythm. (the vagus nerve branch that terminates in the sinoatrial node of the heart)
  • Doctors often describe atrial fibrillation as a disorder of the heart tissue itself. (not a dysautonomia) They explain that the heart tissue itself suffers aberrant signaling that interferes with the proper electrical signaling from the sinoatrial node to the contracting heart muscles. Sometimes this aberrant signaling is described as emanating from the nerve roots of blood vessels, which I guess is a tacit acknowledgment of dysautonomia.
  • Because doctors often view atrial fibrillation as a disorder of the heart tissue itself, surgeons have devised techniques to try to correct the heart tissue, for example the Cox maze procedure. Sometimes these procedures work. Many times, as in the case of my mother, they have absolutely no effect on the atrial fibrillation, perhaps because the atrial fibrillation is actually a dysautonomia of the autonomic nerve that controls the heart rhythm, not due to some other problem with the heart tissue itself.
Hope this helps.
 
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Pyrrhus

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According to researcher Dr. Dane Cook, we still don't know what the scientific relation is between (aerobic) "exercise intolerance" and "PEM/exertion intolerance":


There is currently a theory circulating that tries to link (aerobic) "exercise intolerance" to "PEM/exertion intolerance", by invoking a phenomenon called "ischemia-reperfusion":
  • "Ischemia" simply means a restriction of blood to a tissue, such as a muscle.
  • "Reperfusion" simply means the restoration of blood flow to that tissue.
  • When blood flow is abnormally restricted to a tissue, such as a muscle, and then the blood flow is restored to that tissue, it results in an "ischemia-reperfusion injury".
  • An ischemia-reperfusion injury can have different effects on different tissues.

Specifically, the currently popular "ischemia-reperfusion hypothesis" proposes that PEM is caused by temporarily restricted blood flow to tissues, due to aerobic exercise intolerance (or other problems with blood circulation). Unfortunately, this "ischemia-reperfusion hypothesis" falls flat upon further inspection.

Specifically, the symptoms of PEM are nothing like the symptoms of ischemia-reperfusion injuries, which have been well-studied. Whereas PEM symptoms are generalized and varied, ischemia-reperfusion injuries tend to produce localized, well-defined symptoms.

For example, ischemia-reperfusion injuries in limbs can produce myalgia and paresthesias, which is something like Delayed-Onset Muscle Soreness (DOMS) with temporary Peripheral Neuropathy (PN). On the other hand, PEM presents with a profound muscle weakness called paresis. Inflammation markers in limb ischemia-reperfusion injuries may be elevated, whereas inflammation markers in PEM are not reliably elevated.

An ischemia-reperfusion injury to the brain would produce stroke-like symptoms, as it is essentially a Transient Ischemic Attack (TIA). Although cognitive exertion can trigger PEM, it is not at all clear how cognitive exertion could possibly produce a TIA.

Therefore, PEM/exertion intolerance is not at all similar to the effects of ischemia-reperfusion injuries.
 
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