Image description.The picture shows a scientist using test tubes and a microscope. The title reads ME Association Research Review: Post-Exertional Malaise (PEM) in ME/CFS and Long Covid

ME Association Research Review: Post-Exertional Malaise (PEM) in ME/CFS and Long Covid


There are key biological changes that occur during PEM in many different systems of the body. Research evidence shows that the presence of PEM cannot be disputed and is not due to inactivity or deconditioning.

A brief summary of some of the key findings reveal:

  • different areas of brain activation during and after exertion have been demonstrated with neuroimaging.
  • impaired cardiac function, with orthostatic stress being a significant stressor to induced PEM.
  • gut studies that found an insufficient acute-phase innate immune response following maximal exercise.
  • numerous changes in blood, plasma and urine following exercise, for example: higher blood lactate levels following exercise with more elevated levels resulting in more severe PEM.
  • disturbed metabolic pathways (a series of chemical reactions which start with a substrate and finish with a product) after exercise, that demonstrate a lack of adaption to physical exercise and suggest insufficient energy is being produced to meet demands (2 of these studies are reviewed in detail below).
  • gene expression changes, showing distinct profiles in ME/CFS as well as sex-related differences. These studies also demonstrated that participants were unable to facilitate the transcriptomic changes (gene expression for molecules which help make proteins) that are needed for bodies to recover effectively from exercise (a detailed review of this evidence is presented below).

The evidence from the studies reviewed shows that people with ME/CFS have a different response to exercise than healthy controls, and the findings could be the reasoning behind experiencing PEM and exercise intolerance…


IntroductionResearch: PEM in Long Covid
What is post-exertional malaise (PEM)?Studying PEM and alternatives to CPET
How can we measure PEM?PEM Treatments
What is cardiopulmonary exercise testing (CPET)?Conclusions
Research: PEM in ME/CFSReferences

Audio summary by Dr Katrina Pears

Dr Katrina Pears,
Research Correspondent.
The ME Association.

Dr Katrina Pears - MEA Research Correspondent
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