Fatigue has been defined differently in the literature depending on the field of research. The inconsistent use of the term fatigue complicated scientific communication, thereby limiting progress towards a more in-depth understanding of the phenomenon. Therefore, Enoka and Duchateau (Med Sci Sports Exerc 48:2228–38, 2016, [3]) proposed a fatigue framework that distinguishes between trait fatigue (i.e., fatigue experienced by an individual over a longer period of time) and motor or cognitive task-induced state fatigue (i.e., self-reported disabling symptom derived from the two interdependent attributes performance fatigability and perceived fatigability). Thereby, performance fatigability describes a decrease in an objective performance measure, while perceived fatigability refers to the sensations that regulate the integrity of the performer. Although this framework served as a good starting point to unravel the psychophysiology of fatigue, several important aspects were not included and the interdependence of the mechanisms driving performance fatigability and perceived fatigability were not comprehensively discussed. Therefore, the present narrative review aimed to (1) update the fatigue framework suggested by Enoka and Duchateau (Med Sci Sports Exerc 48:2228–38, 2016, [3]) pertaining the taxonomy (i.e., cognitive performance fatigue and perceived cognitive fatigue were added) and important determinants that were not considered previously (e.g., effort perception, affective valence, self-regulation), (2) discuss the mechanisms underlying performance fatigue and perceived fatigue in response to motor and cognitive tasks as well as their interdependence, and (3) provide recommendations for future research on these interactions. We propose to define motor or cognitive task-induced state fatigue as a psychophysiological condition characterized by a decrease in motor or cognitive performance (i.e., motor or cognitive performance fatigue, respectively) and/or an increased perception of fatigue (i.e., perceived motor or cognitive fatigue). These dimensions are interdependent, hinge on different determinants, and depend on body homeostasis (e.g., wakefulness, core temperature) as well as several modulating factors (e.g., age, sex, diseases, characteristics of the motor or cognitive task). Consequently, there is no single factor primarily determining performance fatigue and perceived fatigue in response to motor or cognitive tasks. Instead, the relative weight of each determinant and their interaction are modulated by several factors.

Many established technologies are limited in analyzing the executive functions in motion, especially while walking. Functional near-infrared spectroscopy (fNIRS) fills this gap. The aim of the study is to investigate the inter-session reliability (ISR) of fNIRS-derived parameters at the prefrontal cortex while walking in people with multiple sclerosis (MS) and healthy control (HC) individuals. Twenty people with MS/HC individuals walked a 12 m track back and forth over 6 min. The primary outcomes were the absolute and relative reliability of the mean, slope coefficient (SC), and area under the curve (A) of the oxy-/deoxyhemoglobin concentrations (HbO/HbR) in the Brodmann areas (BA) 9/46/10. The SC and the A of HbO exhibited a fair ISR in BA10 in people with MS. For the mean and A of the HbR, almost all areas observed revealed a fair ISR. Overall, the ISR was better for HbR than HbO. A fair to excellent ISR was found for most BA of the prefrontal cortex in HC individuals. In total, the ISR of the analyzed fNIRS-derived parameters was limited. To improve the ISR, confounders such as fatigue and mind wandering should be minimized. When reporting the ISR, the focus should be on the mean/A rather than SC.

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Chronic low-back pain is a major individual, social, and economic burden. The impairment ranges from deterioration of gait, limited mobility, to psychosocial distress. Due to this complexity, the demand for multimodal treatments is huge. Our purpose is to compare the effects of a multimodal movement intervention (MI) (coordinative–cognitive exercises and dancing program) with standard physical therapy (PT) on gait, physical function, and quality of life in patients with lumbar spinal stenosis (LSS). The study design is based on a 6-week intervention with a two (group: MI/PT) by two (measurement time points: pre-/post-test) parallel group design with random assignment. Twenty-four subjects (18 female/6 male, 70.8 ± 10.6 years old) diagnosed with LSS were included and randomly allocated to the MI or PT group. The primary outcomes are minimum toe clearance (MTC) and double step length (DSL) variability and the Timed “Up & Go” test (TUG). Secondary outcomes are the Brief Pain Inventory, the short Fall Efficacy Scale–International (sFES-I), and the Oswestry Disability Index. Nine subjects for each group could be analyzed. The MTC variability revealed a significant between-group difference in the posttest (p = 0.008) showing a lower MTC variability for the MI compared to the PT group. The MI group displayed an improved TUG (p = 0.031) and a reduced sFES-I (p = 0.044). The decreased MTC variability and fear of falling as well as the improved functional mobility may contribute to a reduced risk of falling. For the subsequent study, further kinematic and cognitive parameters should be analyzed, and the number of participants has to be increased.Clinical Trial Registration: German Clinical Trial Register (ID: DRKS00021026/URL: https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00021026).

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Background Chronic low back pain (CLBP) is a common medical condition in adults over the age of 50. It is associated with severe disability, ranging from physical impairments to psychosocial distress. Since current treatments provide only small to moderate short-term effects, alternative interventions are required, whereby guidelines recommended multimodal approaches. Dancing can be considered as an inherently multimodal approach, as it requires a combination of physical and cognitive functions. Furthermore, it has already been applied effectively in neurorehabilitation. Therefore, it seems promising to merge a dance-therapeutic component together with motor-cognitive, strength and flexibility exercises in a novel multimodal treatment (MultiMove) to target the impaired everyday mobility and cognition of CLBP patients. The aim of this study is to analyse specific physical, cognitive and psychosocial effects of MultiMove in CLBP patients. Methods A prospective, two-arm, single-blinded, randomized controlled trial will be conducted with an estimated sample size of 100 CLBP patients, assigned to either the MultiMove group or a control group. The intervention group will receive MultiMove twice a week for 60 min each over a period of 12 weeks. The primary outcome will be the mobility and function of the lower extremities assessed by the Timed Up-and-Go Test. Secondary outcomes comprise further physical and physiological functions (e.g. gait variability and haemodynamic response in the prefrontal cortex during motor-cognitive dual tasks), subjective health state (e.g. disability in daily life), executive functions (e.g. cognitive flexibility) and psychosocial aspects (e.g. kinesiophobia). Measures will be taken at baseline, after the intervention and at a 12-week follow-up. It is assumed that MultiMove improves the mentioned outcome parameters. Discussion The combined assessment of changes in physical and cognitive functions as well as neuropsychological aspects in response to MultiMove will allow a better understanding of the motor-cognitive adaptations induced by multimodal exercises in CLBP patients. The specific conclusions will lead to recommendations for the conservative treatment approach in this clinically relevant patient group. Trial registration German Clinical Trial Register (ID: DRKS00021696 / 10.07.2020), https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00021696

Fatigue wurde in Abhängigkeit vom Forschungsfeld (z. B. Neurologie, Psychologie, Bewegungswissenschaft, Physiologie) unterschiedlich definiert. Das führte zu einer uneinheitlichen Verwendung des Begriffes, die den wissenschaftlichen Fortschritt einschränkt. Deshalb wird in diesem Beitrag eine Taxonomie vorgeschlagen, die ein besseres Verständnis von Fatigue bei Personen mit Multipler Sklerose (PmMS) befördert und somit eine eindeutige Charakterisierung des Phänomens und die Applikation effektiver Interventionen zulässt. Zunächst sollte zwischen Trait Fatigue und State Fatigue unterschieden werden. Trait Fatigue beschreibt die Ermüdung/Erschöpfung eines Individuums über einen längeren Zeitraum, z. B. Wochen und Monate. State Fatigue hingegen bezeichnet die akute und transiente Veränderung der motorischen und/oder kognitiven Leistungsfähigkeit sowie verschiedener Wahrnehmungsqualitäten, die im Rahmen einer definierten anhaltenden motorischen und/oder kognitiven Aufgabe auftreten. Die in diesem Beitrag thematisierte motorisch induzierte State Fatigue kann als ein beeinträchtigendes psychophysiologisches Symptom definiert werden, das durch die Abnahme der motorischen Leistungsfähigkeit (motorische Performance Fatigability) und/oder die erhöhte Wahrnehmung von Ermüdung/Erschöpfung (Perceived Fatigability) charakterisiert ist. Diese beiden Dimensionen sind interdependent, nicht separierbar und sollten deshalb simultan quantifiziert werden. Das Ausmaß der motorisch induzierten State Fatigue hängt von den Änderungsraten der motorischen Performance Fatigability sowie Perceived Fatigability ab und wird dadurch auf die Anforderungen der motorischen Aufgabe normalisiert. Die motorische Performance Fatigability wird durch neuronale (Muskelaktivierung) und muskuläre Faktoren (kontraktile Funktion) determiniert, während die Perceived Fatigability vom psychologischen Status des Individuums sowie der Homöostase abhängig ist. Durch den Bezug auf die zugrundeliegenden Mechanismen der motorisch induzierten State Fatigue kann die Analyse der Ursachen der belastungsinduzierten Veränderungen sowie die gezielte Beeinflussung der Mechanismen durch verschiedene Interventionen bei PmMS optimiert werden. Schlüsselwörter: Fatigue, MS, Erschöpfung, Ermüdung, Perceived Fatigability Abstract »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 bodyʼs homeostasis. By referring to the underlying mechanisms of exerciseinduced 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. Keywords: fatigue, perceived fatigability, MS

There are conflicting results regarding the changes in spatio-temporal gait parameters during the 6-min walk test (6MWT) as indicators of gait-related motor performance fatigability (PF) in people with Multiple Sclerosis (pwMS). To further analyze if gait-related motor PF can be quantified using instrumented gait analysis during the 6MWT, we investigated: (i) whether gait parameters recorded during the first or second minute were more stable and thus the better baseline to assess motor PF and (ii) if the minimum toe clearance (MTC) together with “classical” spatio-temporal gait parameters can be used to quantify motor PF in pwMS. Nineteen mildly affected pwMS [12 women/7 men; 47.8 ± 9.0 years; the Expanded Disability Status Scale (EDSS): 2.7 ± 1.0] and 24 healthy controls (HC; 15 women/9 men; 48.8 ± 7.6 years) completed the 6MWT equipped with inertial measurement units. Data were analyzed using the attractor method to compare the stability of gait parameters and, besides “classical” spatio-temporal gait parameters, the MTC was calculated as a potential new marker for motor PF in pwMS as this was shown in healthy older adults. It was found that (i) gait parameters were more stable in the second than in the first minute and (ii) gait-related motor PF could not be detected based on spatio-temporal gait parameters, including the MTC. Descriptive analysis indicated a decrease in MTC variability, which is assumed to be indicative for motor PF, toward the end of the 6MWT in some pwMS. Future studies should investigate gait parameters for the assessment of motor PF in pwMS recorded during more intense and/or longer walking protocols, taking the level of disability into account. Furthermore, using gait parameters recorded in the first minute of the 6MWT as a baseline for the assessment of motor PF should be avoided.