7) The hallmark criteria for the diagnosis are a confirmed prior history of paralytic poliomyelitis; evidence of residual functional deficits, specifically muscle weakness or atrophy, and signs of denervation on electromyography (EMG); a stable period (usually 15 years or more) after recovery from the acute illness; and "the gradual or sudden onset of progressive and persistent new muscle weakness or abnormal muscle fatiguability (decreased endurance).

ME has an incubation period of four to five days and leaves the patient with a chronic encephalopathy and symptoms that include a persistent loss of cognitive and muscular stamina, rapid fatiguability, and slow recovery.

Workers with a variety of chronic medical conditions have identified the need for scheduling flexibility due to fatiguability (Hopkins & Johnston, 1988).