Post-Exertional Malaise

(Post Exertional Malaise)

The NICE Guideline Oct 2021 defines post-exertional malaise or post-exertional symptom exacerbation as:

“The worsening of symptoms that can follow minimal cognitive, physical, emotional or social activity, or activity that could previously be tolerated. Symptoms can typically worsen 12 to 48 hours after activity and last for days or even weeks, sometimes leading to a relapse.”

Post-exertional exacerbation of symptoms or PEM:
• is often delayed in onset by hours or days
• is disproportionate to the activity
• has a prolonged recovery time that may last hours, days, weeks or longer.

The NICE Guideline also states that post-exertional malaise is one of four symptoms which must all be present to suspect a diagnosis of ME/CFS: debilitating fatigue, post-exertional malaise, unrefreshing sleep or sleep disturbance [or both], and cognitive difficulties –  for a minimum of 6 weeks in adults and 4 weeks in children and young people.

Understanding Post-Exertional Malaise (PEM)

A Brief Guide to PEM


• Dr Luis Nacul
Co-principal Investigator CureME London School of Hygiene and Tropical Medicine
Medical Director of the Complex Chronic Diseases Program at British Columbia Women’s Hospital in Vancouver, Canada.

• Dr Christopher Snell
former Chair CFS Advisory Committee to the US Secretary for Health.

• Staci Stevens
Founder the Workwell Foundation

• Prof Mark VanNess
Professor and Co-Chair, Health, Exercise & Sport Sciences,
University of the Pacific. Stockton. CA

• Prof Todd Davenport
Program Director Physical Therapy, University of the Pacific, Stockton. CA

• Dr Nina Muirhead
Dermatology surgeon Buckinghamshire NHS Trust
Chair CMRC Medical Education Working Group

• Dr Nigel Speight
Paediatric Consultant with a special interest in ME
Paediatric medical advisor  ME Association
Medical advisor  25% Group for the Severely Affected.

• Dr David Systrom
Pulmonary and Critical Care Physician at Brigham and Women’s Hospital.
Professor of Medicine, Harvard Medical School.

• Dr Charles Shepherd
Medical advisor for the ME Association.

• Grace, UK ME/CFS biobank patient


• MEA Summary Review: Assessing PEM (Post-exertional malaise)  Charlotte Stephens, March 2019. ME Association website.

Assessment of Post-Exertional Malaise (PEM) in Patients with Myalgic Encephalomyelitis (ME) and Chronic Fatigue Syndrome (CFS): A Patient-Driven Survey by Carly S. Holtzman, Shaun Bhatia, Joseph Cotler and Leonard A. Jason. Diagnostics 20199(1), 26;

Dissecting the nature of post-exertional malaise M Hartle, L Bateman, S D Vernon.Pub. Taylor & Francis online. March 2021

Deconstructing post-exertional malaise in myalgic encephalomyelitis/ chronic fatigue syndrome: A patient-centered, cross-sectional survey: Chu L, Valencia IJ, Gavert DW, Montoya JM.
Published: PLoS One 2018.

• Postexertional malaise in women with chronic fatigue syndrome.
VanNess JM1, Stevens SR, Bateman L, Stiles TL, Snell CR. Journal of  Womens Health  2010

Diminished Cardiopulmonary Capacity During Post-Exertional Malaise 2008
J. Mark VanNess, Christopher R. Snell & Staci R. Stevens  Journal of Chronic Fatigue Syndrome   2007

Characterization of Post–exertional Malaise in Patients With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Authors: B. Stussman, A Williams, J Snow, A Gavin, R Scott, A Nath, B Walitt.
Front. Neurol., 18 September 2020

Patients’ accounts of symptoms – Post Exertional Malaise

“ME/CFS patients describe post–exertional malaise as all-encompassing with symptoms affecting every part of the body, difficult to predict or manage, and requiring complete bedrest to fully or partially recover.”

Characterization of post-exertional malaise in patients with myalgic encephalomyelitis/ chronic fatigue syndrome.  Stussman B, Williams A, Snow J, et al. Frontiers in Neurology. Sept. 2020