Taxonomy and determinants of motor performance fatigability in multiple sclerosis

摘要

?Fatigue? has been defined differently depending on the field of research (e.g., neurology, psychology, exercise physiology), which has led to an inconsistent use of the term, limiting scientific progress. Therefore, this article proposes a taxonomy that promotes a better understanding of fatigue in people with multiple sclerosis (pwMS), allowing a clear characterization of the phenomenon and the application of effective interventions. First, a distinction should be made between trait and state fatigue. Trait fatigue describes the fatigue experienced by an individual over a longer period of time, e.g. weeks and months. State fatigue, on the other hand, describes the acute and temporary change in motor and/or cognitive performance, as well as various perceptual qualities that emerge in the context of a defined sustained motor and/or cognitive task. State fatigue, induced by sustained physical activity, can be defined as a disabling psychophysiological symptom characterized by a decrease in motor performance (motor performance fatigability) and/or an increased perception of fatigue (perceived fatigability). These two dimensions are interdependent, not separable, and should be quantified simultaneously. The magnitude of exercise-induced state fatigue depends on the rates of change in motor performance fatigability as well as perceived fatigability and is thus normalized to the demands of the motor task. Motor performance fatigability is determined by neural (muscle activation) and muscular (contractile function) factors, whereas perceived fatigability depends on the psychological status of the individual as well as the body’s homeostasis. By referring to the underlying mechanisms of exercise-induced state fatigue, analysis of the etiology of the activity-dependent changes can be optimized. This knowledge can be used to apply acute and chronic interventions that specifically influence these mechanisms.