If only I were paramecium too! A case for the complex, intelligent system of anticipatory regulation in fatigue

Abstract

Background: Fatigue is a common term used to describe feelings of tiredness along with observations of reduced physical effort in both health and disease. The study of fatigue has centered mainly on understanding its putative causes. Recently (1990s), fatigue has been researched with an expanded view encompassing its potential origins and purposes in human physiology. Purpose: This review will explore and consider different fatigue models which could assist in the evolving understanding of this human condition. Methods: In this narrative review, Medline and Google Scholar were initially utilized to identify studies and texts documenting the developing understanding of fatigue. Following this, key words were used to locate investigations describing reactions to external stimuli in basic and complex organisms. The term anticipatory regulation was entered to locate studies which evaluated this construct in both health and disease. Results: This review shifts the focus of the fatigue paradigm from the catastrophe model, which emphasizes peripheral energy supply and demand, to the anticipatory regulation model, which focuses on a central regulatory process that anticipates energy demands and makes adjustments to accommodate future demand. The potential for this model to be used to explain the fatigue process in both health and disease is also discussed with respect to specific pathologies. Conclusion: There is now a body of evidence indicating that fatigue may represent a process of anticipatory regulation for maintaining homeostasis.