What are the mechanisms underlying fatigue?

Fatigue is a ubiquitous symptom commonly reported in people with acute and chronic illness. We do not know the specific underlying mechanisms of fatigue; some studies suggest inflammation, the hypothalamic pituitary adrenal (HPA) axis and the autonomic nervous system are implicated in fatigue. We propose longitudinal assessments of self-reported fatigue and inflammatory biomarkers monthly over 1 year to determine those underlying mechanisms of fatigue.