Research Digest – May 2014: Post-Exertional Malaise

Post-exertional malaise (PEM) is characteristic of ME/CFS – considered a hallmark of the disease.  Despite this hallmark status, research has not defined what PEM is or how to measure it.  Patients describe PEM as a crash that occurs following physical or mental exertion.   In his comments to the IOM and in our May Guest Blog Post, Dr. Larry Baldwin refers to it as Post-Exertional Debility, finding that a more suitable name for what he experiences. Reading how patients described crash in “The Voice of the Patient” sounds similar to a phenomenon known as “hitting the wall” – where all energy stores are depleted and functional capacity is lost.

Because PEM is a hallmark of ME/CFS, studying it can provide clues to what is going awry and what could be causing it.  To do this PEM has to be induced using physical or mental challenges.  This month we highlight three recent publications that use exercise and cognitive challenge to study PEM in ME/CFS.


Dr. Betsy Keller and her team at Ithaca College used two cardiopulmonary exercise tests (CPET) 24 hours apart (test:retest) to determine if objective physiological measures such as oxygen consumption and heart rate could be reproduced on the second test.  Keller found that ME/CFS patients were unable to reproduce most physiological measures on the second CPET.  A better understanding of how these physiological measures could be related to PEM and assessed in a way (e.g., blood test) that could be more broadly used in the ME/CFS population may serve as an objective diagnostic marker.

Dr. Mira Meeus and her team Vrije Universiteit Brussel conducted randomized controlled trial to determine how exercise affected pain or analgesia in ME/CFS patients with fibromyalgia, rheumatoid arthritis (RA) patients and healthy controls.  Exercise had positive effects for the RA patients and healthy controls.  In the ME/CFS/FM patients, only when a pain killer (paracetamol) was used was there a positive effect seen and this was negligible.  An explanation for the lack of a positive effect was that the ME/CFS/FM patients were experiencing PEM after the exercise challenge.

Dr. Megan Arroll and her team at the Optimum Health Clinic in the UK published a paper in Fatigue: Biomedicine, Health & Behavior describing their results of a cognitive challenge to induce PEM.  Arroll used a test known as CANTAB as the cognitive challenge.  They measured fatigue using the multidimensional fatigue inventory (MFI) before and 2 days after the CANTAB challenge.  ME/CFS patients had significantly worse general, physical and mental fatigue 2 days after the challenge.  They describe this as the “delayed fatigue effect” and note that this is the first demonstration of PEM being induced with a cognitive challenge.