![]() It is the reduction of effort, resulting from perceived exertion (appraised by motor and sensory inputs) and motivational factors ( 15). Biologically, fatigue is first and foremost an adaptive physiological process. Consequently, central fatigue may depend on flawed integrations of motivational inputs and/or energy expenditure ( 13, 15).Īnother important aspect to take into account regarding central fatigue is the distinction between physiological and pathological fatigue. Hence, fatigue has been suggested to arise when the balance between the energy costs and the expected reward of an action is disrupted ( 16). Motivational inputs, such as expected rewards and benefits, modulate the effort exerted by the individual in any given situation ( 15). For these behaviors, motivational changes appear to be central. These distinctions reflect the behavioral outputs of central fatigue. ![]() Physical fatigue is characterized by a difficulty in performing physical activities, while mental/cognitive fatigue is described as difficulties concentrating and carrying out cognitive tasks ( 14). Central fatigue is further comprised of several dimensions, namely physical fatigue, mental/cognitive fatigue, and motivational changes. This distinction thus lies mainly in the origin of the feeling, with peripheral fatigue developing from peripheral physiological and neuronal systems (e.g., neuromuscular transmission, muscular metabolism, or the cardiovascular system), whereas central fatigue results from changes in the CNS. One distinction relates to peripheral and central fatigue ( 12), with peripheral fatigue described as “the inability to sustain a specified force output or work rate during exercise,” and central fatigue as “the failure to initiate and/or sustain attentional tasks and physical activities requiring self-motivation” ( 13). The multidimensional aspect of fatigue has been addressed in previous literature. Fatigue: A Multidimensional Perspective Definitions of Fatigue One of the reasons may be that fatigue is rarely assessed from a multidimensional perspective. However, despite reported associations between fatigue and circulating levels of inflammatory markers in populations of patients suffering from these diseases ( 10, 11), the specific role and biological mechanisms of inflammation in the development of fatigue symptoms remain elusive. Furthermore, alterations in inflammatory processes are found in patients suffering from medical conditions also characterized by high rates of fatigue, such as cancer survivors and patients with MS or diabetes ( 6). In these conditions, inflammation has been hypothesized as a possible contributor ( 5, 6), based on an extensive literature showing the capacity of inflammatory factors to act on the central nervous system (CNS) and induce behavioral changes, including fatigue ( 7– 9). In some cases, the origin of fatigue can be explained by alterations in muscle metabolism or the cardiovascular system, but for most clinical populations, such as cancer survivors and patients suffering from multiple sclerosis (MS) or chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME), fatigue pathophysiology remains hard to establish. We suggest that the multidimensional aspects of fatigue should be assessed in future studies of inflammation-induced fatigue and that this would benefit the development of effective therapeutic interventions.įatigue is a highly disabling symptom that is common in various medical and psychiatric conditions ( 1– 4). Additionally, the effect of inflammation on specific neuronal processes that may be involved in distinct fatigue dimensions is described. ![]() A description of the features of central fatigue is provided, and the current evidence describing the association between inflammation and fatigue in various medical conditions is reviewed. In this review, we propose that a better assessment of central fatigue, taking into account its multidimensional features, could help elucidate the role and mechanisms of inflammation in fatigue development. While inflammation has been suggested as a potential contributor to the development of fatigue, underlying mechanisms remain poorly understood. 4Institute of Medical Psychology and Behavioral Immunobiology, University Hospital Essen, Essen, Germanyįatigue is a highly disabling symptom in various medical conditions.3Department of Psychology, Stockholm University, Stockholm, Sweden. ![]()
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