postexertion

Postexertion refers to the state or effects that follow physical or mental activity. In physiology, it describes the recovery period after exertion, including changes in heart rate, ventilation, energy substrate use, lactate clearance, and inflammatory signaling. In clinical contexts, the term is often linked to postexertional malaise (PEM), a hallmark feature of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). PEM is characterized by a disproportionate and prolonged worsening of multiple symptoms after additional exertion, with onset typically hours to a day or more later, lasting days to weeks, and can include profound fatigue, myalgia, cognitive impairment, headaches, unrefreshing sleep, sore throat, and orthostatic intolerance.

Postexertion responses are also studied in healthy individuals and patients with other conditions to understand recovery kinetics, such as tachycardia recovery, blood lactate clearance, and autonomic changes. Objective assessments include cardiopulmonary exercise testing and monitoring during the recovery period. In some conditions, postexertional complications such as syncope or chest pain may occur.

Management focuses on pacing and energy management to avoid PEM in susceptible individuals; exercise therapies are individualized, often emphasizing gradual, tolerable activity within the patient’s energy envelope, and careful monitoring by clinicians. Research aims to identify biomarkers of PEM, understand underlying mechanisms such as immune, metabolic, and autonomic dysregulation, and develop targeted interventions.