Exercise intolerance Postexertional symptom exacerbation 2017-04-18T14:35:09Z Post-exertional symptom exacerbation (PESE), also referred to as post-exertional malaise (PEM), is defined as the worsening of symptoms that can follow minimal cognitive, physical, emotional, or social activity, or activity that could previously be tolerated. Symptoms typically worsen 12 to 72 hours after activity and can last for days or even weeks, sometimes leading to a relapse. Postexertional malaise Exercise-induced malaise PEM can be observed in individuals with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), as a post-acute sequela of SARS-CoV-2 infection (long COVID), and occasionally in individuals with mitochondrial disorders or cancer related fatigue. It is often accompanied by exacerabtion or new onset of exhaustion, cognitive impairment, muscle pain, muscle weakness, or other manifestations. The onset of PEM may occur hours or even days after exertion, and recovery from PEM is often slow, taking place over days or weeks or longer. PESE can contribute to the episodic nature of disability in post COVID-19 condition, often presenting as unpredictable fluctuations in symptoms and function.