Symptom variability following acute exercise in myalgic encephalomyelitis/chronic fatigue syndrome: a perspective on measuring post-exertion malaise

ABSTRACTBackground: Consensus for an operational definition of post-exertion malaise (PEM) and which symptoms best characterize PEM has not been established and may be due to variability within and between studies.Purpose: Determine the magnitude of the effect of maximal and submaximal physical exertion on multiple myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) symptoms that are associated with PEM and explore variability among two studies in which mood, fatigue, and pain symptoms were measured before and after exercise.Methods: Symptoms were measured before, and 48 and 72 hours after exercise in study 1 (ME/CFS = 13; Controls = 11) and before and 24 hours after exercise in study 2 (ME/CFS = 15, Controls = 15). Between-study variability was examined by comparing Hedges d effect sizes (95% CI) from studies 1 and 2. Within-patient group variability was examined via inspection of dot density plots.Results: In study 1, large increases in general fatigue (Δ = 1.05), reduced motivation (Δ = 0.93), ...