Post-exertional malaise  (PEM) is a feature of Chronic fatigue syndrome, fibromyalgia, long COVID, Epstein-Barr and Herpes infections, and other conditions. PEM is characterized by malaise following effort and lasting more than 24 hours.

It is not the same as muscle recovery, but may share some features such as nutrient depletion, toxicity, and hormonal dysfunctions.