Learning to feel tired: A learning trajectory towards chronic fatigue.

Chronic fatigue complaints are frequently reported in the general population and fatigue ranks among the most commonly reported symptoms in chronic disease. In contrast to its high prevalence and impact on quality of life, relatively little is understood about the etiology of chronic fatigue. We present a cognitive-behavioral framework, the 'ALT+F' model, that conceptualizes fatigue from an associative learning perspective, and we will evaluate the current evidence for this position. Central to this framework is the notion that interoceptive and exteroceptive stimuli can become associated with the fatigue experience. Consequently, these stimuli may acquire the capacity to elicit fatigue as well as anticipatory fear-related avoidance behavior. We will argue that associative learning processes may contribute to the development of chronic fatigue, fear of fatigue, avoidance of fatigue and activity, and eventually, functional disability. The extent to which associative learning processes give rise to chronic fatigue and fear-related avoidance behavior may depend on a number of risk factors, including perceptual-cognitive biases, sensitization, fatigue catastrophizing, and excessive generalization. The presented framework offers a new window on treatment and intervention options for chronic fatigue.