Fatigue and fatigability in neurologic illnesses: proposal for a unified taxonomy

Pain and fatigue in Parkinson's disease: advances in diagnosis and management

Non-motor symptoms affect over 90% of people with Parkinson's disease at all stages, with pain and fatigue being among the most prevalent yet often neglected in clinical practice. Despite their significant impact, these symptoms are frequently underdiagnosed and inadequately treated, adding substantial burden to patients' lives. The lack of a clear definition and classification of these symptoms has led neurologists to underestimate their presence among people with Parkinson's disease and limited the ability to address them with mechanism-based care and effective treatments. Managing these symptoms is challenging because of the lack of robust, specifically designed, randomized-controlled trials on effective treatments. This review delves into the current understanding of diagnosing, assessing, and treating pain and fatigue in Parkinson's disease, highlighting critical knowledge gaps and suggesting future research directions. The framework emphasizes improving classification methods, deepening our understanding of the underlying pathophysiology, evaluating treatment impacts on pain and fatigue, and leveraging longitudinal data collection through consensus-based methodology. By addressing these critical areas, we strive to enhance the management of these debilitating non-motor symptoms and ultimately improve patients' quality of life.

Overnight changes in performance fatigability and their relationship to modulated deep sleep oscillations via auditory stimulation

Deep sleep oscillations are proposed to be central in restoring brain function and to affect different aspects of motor performance such as facilitating the consolidation of motor sequences resulting in faster and more accurate sequence tapping. Yet, whether deep sleep modulates performance fatigability during fatiguing tasks remains unexplored. We investigated overnight changes in tapping speed and resistance against performance fatigability via a finger tapping task. During fast tapping, fatigability manifests as a reduction in speed (or "motor slowing") which affects all tapping tasks, including motor sequences used to study motor memory formation. We further tested whether overnight changes in performance fatigability are influenced by enhancing deep sleep oscillations using auditory stimulation. We found an overnight increase in tapping speed alongside a reduction in performance fatigability and perceived workload. Auditory stimulation led to a global enhancement of slow waves and both slow and fast spindles during the stimulation window and a local increase in slow spindles in motor areas across the night. However, overnight performance improvements were not significantly modulated by auditory stimulation and changes in tapping speed or performance fatigability were not predicted by individual changes in deep sleep oscillations. Our findings demonstrate overnight changes in fatigability but revealed no evidence suggesting that this effect is causally linked to temporary augmentation of slow waves or sleep spindles. Our results are important for future studies using tapping tasks to test the relationship between sleep and motor memory consolidation, as overnight changes in objectively measured and subjectively perceived fatigue likely impact behavioural outcomes.

Development of self-report measures of physical, mental, and emotional fatigability: the michigan fatigability index (MIFI)

PURPOSE

To develop item banks and static short-forms for a patient reported outcome measure of perceived physical, mental, and emotional fatigability-the Michigan Fatigability Index (MIFI).

METHODS

Building on earlier qualitative work, this study utilized cognitive interviews in samples representing the general adult population across the lifespan, people with multiple sclerosis (MS), or people with fibromyalgia (FM) to develop initial item pools. A nationwide cross-sectional survey study in MS and FM samples was used to field test items to develop item banks.

RESULTS

Exploratory and confirmatory factors analyses indicated single underlying dimensions for each of the MIFI subdomains, and a graded response model (GRM) supported item fit of 42, 28, and 23 items to the physical, mental, and emotional fatigability items banks, respectively. Differential item functioning was not detected for age, condition (FM vs. MS), education level, ethnicity, race, or sex. Expert review and GRM calibration data was used to inform the selection of three 6-item short forms that assess physical, mental, and emotional fatigability and to program associated computer adaptive tests.

CONCLUSION

The MIFI shows initial evidence of good psychometric properties. Users can administer the MIFI as a static short form and efforts are underway to provide access to the measure as a computer adaptive test. T-Score scale conversion allows comparison of individual scores to a normative clinical sample with a wide range of fatigability.

Digital Biomarkers and AI for Remote Monitoring of Fatigue Progression in Neurological Disorders: Bridging Mechanisms to Clinical Applications

Digital biomarkers for fatigue monitoring in neurological disorders represent an innovative approach to bridge the gap between mechanistic understanding and clinical application. This perspective paper examines how smartphone-derived measures, analyzed through artificial intelligence methods, can transform fatigue assessment from subjective, episodic reporting to continuous, objective monitoring. The proposed framework for smartphone-based digital phenotyping captures passive data (movement patterns, device interactions, and sleep metrics) and active assessments (ecological momentary assessments, cognitive tests, and voice analysis). These digital biomarkers can be validated through a multimodal approach connecting them to neuroimaging markers, clinical assessments, performance measures, and patient-reported experiences. Building on the previous research on frontal-striatal metabolism in multiple sclerosis and Long-COVID-19 patients, digital biomarkers could enable early warning systems for fatigue episodes, objective treatment response monitoring, and personalized fatigue management strategies. Implementation considerations include privacy protection, equity concerns, and regulatory pathways. By integrating smartphone-derived digital biomarkers with AI analysis approaches, the future envisions fatigue in neurological disorders no longer as an invisible, subjective experience but rather as a quantifiable, treatable phenomenon with established neural correlates and effective interventions. This transformative approach has significant potential to enhance both clinical care and the research for millions affected by disabling fatigue symptoms.

Differences in frontal cortical brain function between individuals suffering from pathological mental fatigue following acquired brain injury and healthy individuals

Pathological mental fatigue (PMF) is a common health concern after acquired brain injuries, with tens of millions affected globally each year. Neuroimaging methods show promising results for establishing associations between PMF and brain function. The aim of this study was to investigate whether and how neural functional activity and connectivity differ during rest and cognitive tasks between people with PMF and healthy controls. Twenty participants suffering from PMF after an acquired brain injury (ABI; stroke or traumatic brain injury) and 19 healthy controls were recruited and underwent cognitive tests and functional near infrared spectroscopy (fNIRS) assessments. The results show that the PMF group and controls exhibited different functional brain activation in the frontal cortex, concerning both neural connectivity and activity. More specifically, the PMF group showed higher Global Efficiency and lower Modularity during resting state and when performing the cognitive tasks Digit Symbol Coding and Symbol Search. The groups also differed in peak oxygenated hemoglobin during the BASE task, with lower oxygenation in the PMF group. In addition, the PMF group was significantly slower than the control group in both neutral and incongruent Stroop trials. However, no group differences were observed in neural activity during the Stroop task, and nor were there differences in reactivity or proactivity as measured using the AX-CPT test. This study has developed the knowledge on the brain correlates of PMF. Future studies should explore the theoretical and practical implications of these results.

The Brain Fatigue Syndrome-Symptoms, Probable Definition, and Pathophysiological Mechanisms

Fatigue is a common consequence of traumatic brain injury, neurological diseases or developmental disorders, and systemic inflammatory diseases, including autoimmune conditions that affect the brain. This condition is characterized by reduced endurance for cognitive tasks, diminished quality of life, and impaired work capacity. In addition to cognitive difficulties, individuals often experience disproportionately long recovery times after demanding tasks, emotional instability, stress sensitivity, sensory sensitivity, impaired ability to initiate activities, and sleep disturbances. Tension headaches frequently occur when the brain is excessively activated by mental activity. In this paper, we propose the term "Brain Fatigue Syndrome" (BFS) as a collective name for the symptoms closely associated with this pathological fatigue resulting from brain impact. BFS can be identified through interviews and measured using the self-assessment instrument, the Mental Fatigue Scale (MFS). We suggest potential underlying mechanisms at the cellular level for the BFS symptom complex, including astrocyte dysfunction with impaired glutamate signaling and glucose uptake, mitochondrial dysfunction, blood-brain barrier dysfunction, and the activation of microglia and mast cells. In conclusion, BFS suggests a general brain impact. The symptoms associated with BFS typically resolve when the injury or disease heals. However, in some individuals, BFS persists even after the injury or illness has ostensibly healed.

A new mindfulness and psycho-educative program for treatment of brain fatigue, evaluated after an acquired brain injury and multiple sclerosis

Background: Fatigue is a common long-term problem after illnesses affecting the brain, having substantial impact on work ability, social activities, and quality of life. Treatment has been requested in the healthcare and by patients. The aim of this randomized pilot study is to evaluate a new Brain Fatigue and Mindfulness program (BF-M) for participants suffering from long-term fatigue after an acquired brain injury or Multiple Sclerosis. BF-M consists of six biweekly group meetings. Meditation is practiced, knowledge is imparted about fatigue and participants have time to share and discuss common issues. Methods: A mixed method research design is used with quantitative and qualitative methods. Sixteen participants completed BF-M and 16 controls on waitlist responded to questionnaires before and after the intervention. Results: After the program, the BF-M group had a significant reduction in BF and anxiety compared to the controls. The analysis of 13 interviews with BF-M participants suggested that: (1) BF-M became a space for the participants to exchange and share experiences associated with BF; (2) the participants felt more understood and less alone; and (3) they learned how to better understand and live with brain fatigue. Conclusions: This study showed that BF-M may reduce brain fatigue and help participants to better manage their difficulties. Based on this pilot study, we suggest that BF-M may be considered as a rehabilitation option for brain fatigue. However, more confirmatory research with larger and different patient groups is needed.

Effect of Orthostatic Tremor on Quality of Life - a Cohort Study

Background

Orthostatic tremor (OT) is characterized by a lower extremity tremor causing unsteadiness while standing, urging patients to lean, walk, or sit to ease symptoms. This severely disrupts daily life and reduces quality of life (QoL), though the extent of QoL impairment remains largely unknown. The objective of this cohort study was to evaluate the effect of OT on daily functioning and well-being over time.

Methods

In this prospective single-center and community based cohort study, OT patients annually completed self-report scales from 2018 to 2024, including the Dutch OT-questionnaire, Hospital Anxiety and Depression Scale (HADS), (instrumental) Activities of Daily Living, and the Short Form-36 (SF-36) to evaluate QoL.

Results

Fifty-three OT patients participated in the study. OT patients showed reduced well-being compared to the general population based on outcomes from the SF-36 and HADS, with 30 out of 53 patients experiencing potential or suspected depression and/or anxiety. Despite viewing OT as progressive, most patients saw no significant changes in overall well-being or daily functioning, although a significant difference was found between baseline and last follow-up for physical role limitation.

Discussion

Although OT patients report reduced well-being, both daily functioning and overall well-being remained stable over time, despite progressive symptoms. This is likely due to patients increased ability to adapt to OT symptoms. Additionally, a substantial portion had potential or suspected depression or anxiety.

Highlights

Orthostatic tremor (OT) patients report reduced quality of life, with worsened walking ability and increased weather sensitivity over time. Despite this, daily functioning and overall well-being remained stable throughout the study. A significant portion of patients also showed potential or suspected depression and/or anxiety.

Characterizing Patient-Reported Fatigue Using Electronic Diaries in Neurodegenerative and Immune-Mediated Inflammatory Diseases: Observational Study

Background

Fatigue is a prevalent and debilitating symptom in many chronic conditions, including immune-mediated inflammatory diseases (IMIDs) and neurodegenerative diseases (NDDs). Fatigue often fluctuates significantly within and between days, yet traditional patient-reported outcomes (PROs) typically rely on recall periods of a week or more, potentially missing these short-term variations. The development of digital tools, such as electronic diaries (eDiaries), offers a unique opportunity to collect granular, real-time data. However, the feasibility, adherence, and comparability of eDiary-based assessments to established PROs require further investigation.

Objective

This study aimed to evaluate the feasibility and acceptability of using a high-frequency eDiary to capture intraday variability in fatigue and to compare eDiary data with scores obtained from the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F), a validated weekly recall PRO.

Methods

Data were collected from 159 participants enrolled in the IDEA-FAST (Identifying Digital Endpoints to Assess Fatigue, Sleep and Activities in Daily Living in Neurodegenerative Disorders and Immune-Mediated Inflammatory Diseases) feasibility study; a 4-week prospective observational study conducted at 4 European centers. Participants included individuals with NDDs (n=39), IMIDs (n=78), and healthy volunteers (n=42). Participants used an eDiary to report their physical and mental fatigue levels up to 4 times daily on a 7-point Likert scale (0=low and 6=high). Adherence was calculated as the proportion of completed eDiary entries relative to the total expected entries. Correlations between averaged eDiary scores and weekly FACIT-F scores were analyzed.

Results

Adherence to the eDiary protocol was 5505/8880 (61.99%) overall, varying by cohort, with the highest adherence (1117/1200, 93.07%) observed in the primary Sjögren syndrome cohort and the lowest adherence in the Parkinson disease (410/960, 42.7%) and Huntington disease (320/720, 44.4%) cohorts. The average adherence was 430/1680 (43.45%) in the NDD cohorts and 3367/4560 (73.84%) in the IMID cohorts. Fatigue levels showed clear diurnal variation, with significantly higher fatigue reported in the evening compared to the morning (P<.001). A moderate correlation (Spearman=0.46, P<.001) was observed between eDiary fatigue scores and FACIT-F scores, with stronger cohort-specific associations for certain FACIT-F items. These results indicate that eDiaries provide complementary insights to weekly PROs by capturing intraday fluctuations in fatigue.

Conclusions

This study demonstrates the feasibility, acceptability, and validity of using high-frequency eDiaries to assess fatigue in chronic conditions. By effectively detecting intra- and interday fatigue variations, eDiaries complement traditional PROs such as FACIT-F, offering a more nuanced understanding of fatigue patterns. Future research should explore optimized eDiary protocols to balance participant burden with data granularity.

[Cross-sector Management of Medical Treatment and Integrated Forms of Therapy for Post-COVID-19 Patients with Fatigue and Sensorimotor Instability]

For the medical treatment of post-COVID-19 syndrome, only a few cross-sector medical treatment networks, such as the Post-COVIDLMU CONCEPT [1], are currently being implemented. However, no causal therapy can be reliably recommended based on evidence-based criteria. A cross-sector, doctor-led treatment management will be inaugurated for post-COVID-19, initially focusing on the syndrome of fatigue/immunometabolic depression (as a target for precision medicine) and sensorimotor instability as a cognitive parameter. The corresponding parameters will be recorded and analyzed in real time and at the same time become an important environmentally stable training object. The use of internet and mobile-based interventions represents an essential component here.Changes in the leading syndromes of fatigue and sensorimotor instability through stress-controlled standardized training therapy, intensified cognitive behavioral therapy and the process design of interdisciplinary therapy management in compliance with the guidelines of the Federal Joint Committee (G-BA) for cross-professional and cross-sector care for post-COVID-19 patients were the overarching goals of an intervention study at the post-COVID-19-Center Lausitz over a 3-year period (Q1-2021-Q2-2024). The results of a stress-controlled intervention study were integrated into the derivation, design and evaluation of a cross-sector management process. The outcome and management of the training therapy were assessed based on the post-COVID-19 key symptoms and motor fatigue parameters. A secondary psychosomatic syndrome that emerged during treatment was examined using cognitive fatigue parameters.With the stress-controlled sensorimotor intervention integrated into the designed management process as well as intensified cognitive behavioral therapy, improvements in post-COVID-19 key symptoms as well as in the parameters of motor and cognitive fatigability were achieved. The timing of the start of the process stages of the overall management had an influence on the outcome of the treatment path. Intensification of cognitive behavioral therapy also had positive effects, resulting in an increasing level of activity and self control in patients.

Lack of pre-movement facilitation as neurophysiological hallmark of fatigue in patients with Parkinson's disease: A single pulse TMS study

BACKGROUND

Fatigue is a debilitating symptom in Parkinson's disease (PD), significantly affecting quality of life. Despite its prevalence, the underlying neurophysiological mechanisms remain poorly understood. Recent evidence suggests that deficits in cortical motor preparation processes may contribute to PD-related fatigue.

METHODS

This study investigated premovement facilitation (PMF), a marker of corticospinal excitability during motor preparation, in 20 healthy subjects (HS) and 28 PD patients, subdivided into those with fatigue (PDwF, n = 14) and without fatigue (PDwoF, n = 14). Participants performed a reaction time (RT) task involving thumb abduction following a visual go signal, while transcranial magnetic stimulation (TMS) was applied over the primary motor cortex (M1) at intervals of 50, 100, and 150 ms before movement onset. Motor-evoked potentials (MEPs) were recorded from the abductor pollicis brevis (APB) and the task-irrelevant abductor digiti minimi (ADM).

RESULTS

In HS and PDwoF, MEP APB amplitude increased progressively when TMS was applied at 150, 100, and 50 ms before movement onset, reflecting intact PMF, with the greater MEP APB amplitude at the shorter interval (50 ms). However, in PDwF patients, PMF was absent on the most affected side, while it remained preserved on the less affected side. Furthermore, the absence of PMF correlated with fatigue severity (FSS scores) and rigidity subscores, highlighting a link between impaired motor preparation and clinical symptoms.

CONCLUSION

These findings suggest that cortical dysfunction in motor preparation contributes to PD-related fatigue, particularly in the most affected hemisphere. The observed PMF deficits provide a potential neurophysiological marker for fatigue in PD, supporting future investigations into targeted therapeutic interventions to restore motor excitability and alleviate fatigue symptoms.

Anti-central fatigue effects of myelophil in 5-HTergic hyperactivity mice model

BACKGROUND

Myelophil is a standardized ethanol extract of Astragali Radix and Salviae Miltiorrhizae Radix, which has been developed based on clinical experience in traditional Korean medicine practices for patients with unexplained chronic fatigue, including myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Our previous studies demonstrated Myelophil's clinical efficacy in ME/CFS, as well as its brain-related activities in animal models. However, the underlying pharmacological mechanisms remain unclear. Recently, we identified serotonergic hyperactivity as a key pathophysiological factor in central fatigue, such as ME/CFS. Therefore, in the present study, we aimed to investigate the mechanisms by which Myelophil exerts its effects, particularly in the context of a 5-HTergic hyperactivity model.

METHOD

To verify the action mechanisms of Myelophil on serotonergic hyperactivity condition, we herein assessed its anti-central fatigue properties using a fluoxetine-treated mice model. Male C57BL/6 N mice (9 weeks old) were subjected to periodic intraperitoneal (IP) injections of fluoxetine for 4 weeks and the mice were simultaneously oral administered Myelophil (0, 50, or 100 mg/kg) or ascorbic acid (100 mg/kg).

RESULT

Four-week injection of fluoxetine notably increased serotonin (5-hydroxytryptamine, 5-HT) activity, as evidenced by immunofluorescence staining and Western blot assays in the raphe nuclei (RN), and induced central fatigue-like behaviors in the nest building test, wheel running test, rota-rod test, plantar test, and open field test. Meanwhile, Myelophil (100 mg/kg) administration significantly ameliorated those fatigue-related behaviors including pain sensitivity. Furthermore, the anti-fatigue effects of Myelophil were corroborated by changes in serotonin-related parameters (serotonin transporter; 5-HTT and vesicular monoamine transporter 2; VMAT2), as well as neurotrophic markers including c-Fos and brain-derived neurotrophic factor (BDNF) in the RN.

CONCLUSION

These results provide experimental evidence suggesting the potential mechanisms by which Myelophil may alleviate central fatigue associated with hyper-5-HTergic activity.

CLINICAL TRIAL NUMBER

Not applicable.

Molecular-Informed Network Analysis Unveils Fatigue-Related Functional Connectivity in Parkinson's Disease

BACKGROUND

Fatigue in Parkinson's disease (PD) is a prevalent and debilitating non-motor symptom. Despite its significant impact on quality of life, the underlying neurochemical and network-based mechanisms remain poorly understood.

OBJECTIVES

This observational study applied a multimodal imaging approach to explore potential links between the functional connectivity of neurotransmitter-specific circuits and fatigue in a sample of patients with PD.

METHODS

We acquired resting-state functional magnetic resonance imaging data in 35 patients with PD including 18 with clinically significant fatigue and 17 without. We applied the receptor-enriched analysis of functional connectivity by targets (REACT) pipeline to derive patients' specific molecularly enriched networks informed by the spatial distribution of the dopamine, noradrenaline, serotonin transporters, and metabotropic glutamate 5 receptors as assessed using molecular imaging data in independent samples of healthy controls. We then conducted whole-brain analyses inspecting both categorical differences between groups of patients with and without clinically significant fatigue, and associations exploring the full within-sample variation in symptom ratings.

RESULTS

We found a significant decrease in noradrenaline-enriched and glutamate-enriched functional connectivity in key regions, belonging to the sensorimotor, salience, and default mode network, with increasing fatigue severity. Notably, noradrenaline-enriched functional connectivity reductions were widespread, while glutamate-enriched functional connectivity reductions were more restricted to the supplementary motor area. No significant relationships between fatigue and dopamine or serotonin-enriched functional connectivity were found.

CONCLUSIONS

These findings offer supportive evidence for the putative involvement of the noradrenaline and glutamate systems in the genesis of fatigue in PD, opening new directions for treatment development exploring these neurochemical systems. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The Role of MAO-B Inhibitors in Fatigue in Parkinson's Disease: A Narrative Review

Background: Fatigue is a common and debilitating non-motor symptom (NMS) in Parkinson's disease (PD), significantly affecting patients' quality of life. MAO-B inhibitors are effective therapy for motor symptoms and fluctuations and may also play a role in fatigue management. Methods: We searched PubMed for English-language articles (January 1978-August 2024) using keywords including "selegiline", "rasagiline", "safinamide", "MAO-B", "fatigue", and "Parkinson's disease". Clinical trials, observational, and preclinical studies were included. Results: While the role of MAO-B inhibitors in fatigue remains unclear, evidence suggests potential benefits. Selegiline has shown effectiveness in improving fatigue in animal models, supporting its potential utility in treating fatigue and motivational impairments in PD patients. Rasagiline has been associated with reduced fatigue progression in early PD, with some studies showing significant improvements compared to placebo. Safinamide, with its dual action as an MAO-B inhibitor and glutamate modulator, may further enhance fatigue management. Its ability to reduce glutamate release is particularly relevant, given the role of glutamate overactivity in PD-related fatigue. Studies indicate safinamide can significantly reduce fatigue levels. Conclusions: Fatigue in PD is a complex symptom with multiple contributing factors. While MAO-B inhibitors may support fatigue management, their precise role and optimal use require further investigation.

Experimental autoimmune encephalomyelitis causes skeletal muscle dysfunction in mice

Multiple sclerosis (MS) is a neuroinflammatory disease affecting the brain and spinal cord and characterized by demyelination, neurodegeneration and chronic inflammation. More than 90% of people with MS present with peripheral muscle dysfunction and a progressive decline in mobility. Current treatments attenuate the inflammatory processes but do not prevent disease progression. Therefore, there remains an unmet medical need for new and/or additional therapeutic approaches that specifically improve muscle function in this patient population. The development of novel treatments targeting skeletal muscle dysfunction in MS will depend on suitable preclinical models that can mimic the human musculoskeletal manifestations of MS. Using a non-invasive approach to assess muscle function, we demonstrate in vivo that Experimental Autoimmune Encephalomyelitis (EAE) impairs skeletal muscle strength. Our data reveal a 28.3% (p < 0.0001) lower muscle force in animals with EAE compared to healthy control mice during electrically evoked tetanic muscle contractions that occur at intervals of 0.25 s and thus mimic fatiguing tasks. As we conduct force measurements by direct transcutaneous muscle stimulation in anesthetized animals, our setup allows for the repeated evaluation of muscle function, and in the absence of primary fatigue or reduced nerve input which constitute important confounding factors in MS. Taken together, our data highlight important similarities between MS in humans and EAE in mice with regards to skeletal muscle contractile impairments, and provide first evidence for a non-invasive in-vivo setup that will enable the preclinical profiling of novel drug candidates directed at specifically improving muscle function in MS.

Fatigue Is Associated With Perceived Effort and 2-Dimensional Reach Performance After Stroke

BACKGROUND AND PURPOSE

Poststroke fatigue (PSF) is prevalent and often manifests as high perceived effort during activities. Little is known about how PSF influences goal-directed reaching after stroke. The purpose of this study was 2-fold (1) to evaluate how perceived effort changed when individuals with stroke performed a reaching task with various demands and (2) to determine whether PSF was associated with perceived effort during reaching and reach performance.

METHODS

Thirty-six individuals with chronic stroke performed 2-dimensional reach actions under varied conditions with the more and less affected arms. Perceived effort during reaching was assessed using rating of perceived exertion (RPE) and Paas Mental Effort Rating Scale (MERS). Derived reach kinematics were used to quantify reach performance. The Fatigue Severity Scale (FSS) was administered to assess fatigue severity.

RESULTS

Perceived effort was higher when participants reached with the more affected arm, reached toward far and small targets, and performed memory-guided reaching. Both RPE and MERS significantly correlated with the FSS score ( r = 0.50 and 0.35, respectively, P < 0.05). Further, FSS correlated with movement time during the more affected arm reaching (ρ = 0.40, p < 0.05) and reach performance discrepancy between the fast and self-selected speed conditions when participants performed with the less affected arm (ρ = 0.36, P < 0.05). Exploratory analysis revealed that the relationship between fatigue and reach control appeared to be modulated by task demand.

DISCUSSION AND CONCLUSIONS

PSF is associated with perceived effort during reaching and reach performance after stroke. These relationships might offer insights into arm performance in the real world after stroke.

VIDEO ABSTRACT

for more insights from the authors Supplemental Digital Content available at http://links.lww.com/JNPT/A476.

Non-pharmacological treatment options for fatigue: A systematic review of RCTs in adults

OBJECTIVE

Fatigue is a significant contributor to the burden experienced by patients with chronic disorders. The development of standardized treatments is challenging due to the lack of consensus concerning the etiology of fatigue. The aim of this systematic review is to provide an overview of non-pharmacological interventions for fatigue. The efficacy and differences in fatigue treatment across conditions will be explored.

METHODS

A systematic literature search was conducted using the databases PubMed, Web of Science, PsycInfo and CINAHL. Trials were eligible when (1) adult patients (≥ 18 years old) with disorders causing fatigue were included, (2) non-pharmacological interventions performed, (3) treatment was compared to standard care, placebo or active control group, (4) fatigue was the only primary outcome assessed with a multidimensional tool, and (5) a randomized controlled trial (RCT) design was applied.

RESULTS

7592 papers were screened. 91 RCTs were eligible, with data reported in 95 papers. Specific fatigue interventions were present for a broad range of conditions. Findings demonstrated promising evidence for physical activity, CBT, online programs and multidimensional modules. Additional types of interventions were effective, but evidence was limited due to risk of bias and small sample sizes. Due to high heterogeneity concerning methodology, a meta-analysis was not possible.

CONCLUSION

Several non-pharmacological treatment options for fatigue are promising. No clear evidence was found that fatigue should be treated differently depending on the underlying condition. However, further research is necessary with a focus on a transdiagnostic approach to fatigue, high study quality and long-term follow-ups.

Theta-Burst Stimulation Modulates Exercise Performance by Influencing Central Fatigue and Corticospinal Excitability

PURPOSE

Theta-burst stimulation (TBS) over the primary motor cortex modulates activity of the underlying neural tissue, but little is known about its consequence on neuromuscular fatigue and its neural correlates. This study aimed to compare the effects of facilitatory versus inhibitory TBS on the neuromuscular fatigue and excitability/inhibition of the corticospinal pathway in an unfatigued/fatigued muscle.

METHODS

The effects of three TBS protocols (facilitatory/intermittent: iTBS; inhibitory/continuous: cTBS, and sham: sTBS) were tested on exercise performance, neuromuscular function, and corticospinal excitability and inhibition in 20 young healthy participants. Transcranial magnetic and peripheral electrical stimulations were used at baseline, following TBS (unfatigued state), and after a fatiguing sustained contraction (fatigued state) at 35% of the maximal voluntary isometric contraction (MVIC) of the elbow flexors.

RESULTS

Time-to-task failure was shorter for cTBS (142 ± 51 s) and longer for iTBS (214 ± 68 s) compared with sTBS (173 ± 65 s) ( P < 0.05). In an unfatigued state, cTBS reduced MVIC and voluntary activation (VA), increased motor-evoked potential, and silent period ( P < 0.05), whereas iTBS did not cause any change. In a fatigued state, MVIC and VA decreased in all TBS sessions ( P < 0.05). However, the reduction in VA was larger after cTBS (Δ -18 ± 18%) compared with iTBS (Δ-3 ± 5%), and sTBS (Δ-9 ± 9%) ( P < 0.001). Furthermore, the increase in motor-evoked potential and silent period were greater for cTBS ( P < 0.05), compared with iTBS and sTBS ( P < 0.05).

CONCLUSIONS

Facilitatory TBS augments exercise performance that is independent of central parameters and corticospinal mechanisms, whereas inhibitory TBS attenuates exercise performance through an exacerbation in the development of central fatigue and possibly intracortical inhibition.

Relationship among depression, fatigue, and sleep after traumatic brain injury: The role of physical exercise as a non-pharmacological therapy

Traumatic brain injury (TBI) is a burdensome condition frequently associated with an increased risk of psychiatric disorders. Although the exact molecular signaling pathways have not yet been fully defined, the compromised integrity of functional brain networks in regions such as the prefrontal cortex and anterior cingulate cortex has been linked to persistent symptoms, including depression, fatigue, and sleep disorders. Understanding how TBI affects neural physiology enables the development of effective interventions. One such strategy may be physical exercise, which promotes neural repair and behavioral rehabilitation after TBI. However, there are caveats to consider when interpreting the effects of physical exercise on TBI-induced mental health issues. This review will highlight the main findings from the literature investigating how different physical exercise protocols affect the progression of TBI-induced depression, fatigue, and sleep disturbances. Furthermore, we aim to explore potential neurobiological pathways that explain how physical exercise influences depression, fatigue, and sleep following TBI.

Evaluation of fatigue and fatigability in people with Duchenne muscular dystrophy using a dynamic arm support - a pilot study

BACKGROUND

Due to progressive muscle wasting and weakness in patients with Duchenne Muscular Dystrophy (DMD), physical fatigability increases, upper extremity function reduces, which negatively impacts quality of life. Assistive technology such as dynamic arm supports (DAS) may help reduce this fatigability. This study aims to assess whether the novel Yumen 'EXone' DAS can reduce upper extremity fatigue and fatigability in DMD patients and healthy controls (HC), both with and without the DAS. Additionally, longitudinal changes in DMD patients were evaluated.

METHODS

Five DMD patients from the Yumen Bionics pioneer program and five HCs participated. Two submaximal tests simulating drinking and reaching were performed for two minutes, each with and without DAS. DMD participants completed these tests twice, at baseline (T0) and after 6-9 months (T1), while HCs completed them once. Physical fatigability was measured by the number of repetitions and changes in surface electromyography (sEMG) amplitude. Subjective fatigue was assessed using the Borg Scale (6-20) Rate of Perceived Exertion (RPE).

RESULTS

DMD participants generally performed more repetitions with the DAS than without. HCs showed similar or increased repetitions with the DAS. Assessing fatigability with sEMG was difficult due to the compensatory mechanisms used for the tests. Subjective fatigue scores on the Borg Scale were lower with the DAS for both DMD patients and HCs.

CONCLUSION

The Yumen 'EXone' DAS effectively reduces both fatigue and fatigability in DMD patients and healthy controls. Despite the methodological shortcomings, this research is one of the first studies investigating the impact of DAS on fatigue and fatigability.

Perceived fatigue does not alter effort-based decision making but does undermine confidence in the ability to perform physical actions

Fatigue may affect the decision to deploy effort (cost) for a given rewarded outcome (benefit). However, it remains unclear whether these fatigue-associated changes can be attributed to simply feeling fatigued. To investigate this question, twenty-two healthy males made a series of choices between two rewarded options: a fixed, no effort option, where no physical effort was required to obtain a set, low reward vs. a variable, effortful option, in which both the physical effort requirements (i.e. different durations of a sustained contraction performed in the lower limbs) and rewards (i.e. greater monetary incentives) was varied. Effort-based choices were made under two conditions: (1) a rested (control) state, (2) a pre-induced state of perceived fatigue, evoked through physical exertion in the upper-limbs, thus controlling for the physical manifestation of fatigue (i.e. decline in muscular force production in the lower limbs) on the decision process. Though prior physical exertion increased the perception of fatigue, participants choices did not significantly differ between control and fatigue conditions. Across both conditions, participants demonstrated an anticipated aversion to effort, with greater effort requirements reducing the decision to engage in actions associated with higher rewards. However, in the fatigue state only, decision time was prolonged and self-reported confidence in individuals' ability to perform high effort actions was reduced. The findings suggest that a perceived state of fatigue does not necessarily alter cost/benefit comparisons within effort-based decisions, but may introduce greater uncertainty within choice and reduce self-confidence. These findings evidence altered evaluative processes during decision making under conditions of fatigue.

Fatigue in multiple sclerosis: still elusive after all these years

This scientific commentary refers to 'Fatigue in early multiple sclerosis: MRI metrics of neuroinflammation, relapse and neurodegeneration', by Meijboom et al. (https://doi.org/10.1093/braincomms/fcae278).

Exploring Fatigue in Parkinson's Disease: A Comprehensive Literature Review

Fatigue is one of the most prevalent and debilitating non-motor symptoms of Parkinson's disease (PD), affecting up to two-thirds of patients and significantly impacting quality of life. This review provides a comprehensive analysis of its complex pathophysiology, prevalence, clinical presentation, assessment methods, and current management strategies. Fatigue in PD is linked to dysfunction in dopaminergic and non-dopaminergic pathways, neuroinflammation, genetic predispositions, and metabolic dysregulation. Reported prevalence rates range from 36% to 60%, highlighting the need for standardized assessment tools and a universally accepted definition. Clinically, fatigue is characterized by an overwhelming and abnormal sense of exhaustion, often preceding motor symptoms by years. Distinguishing it from sleepiness, apathy, and depression is crucial for accurate diagnosis and treatment. Assessment primarily relies on patient-reported scales, such as the Fatigue Severity Scale and the Parkinson's Disease Fatigue Scale. Management includes both pharmacological and non-pharmacological approaches, with medications like methylphenidate and rasagiline showing potential, alongside physical exercise, cognitive behavioral therapy, and sleep disorder management. Further research is essential to unravel the underlying mechanisms, identify objective biomarkers, and develop more effective, targeted treatments for this burdensome symptom.

Persistent high levels of perceived fatigue are not associated with hypermetabolism in patients with amyotrophic lateral sclerosis

Objective: Fatigue is a common symptom in amyotrophic lateral sclerosis (ALS). Little is known about factors that contribute to fatigue, and whether levels of fatigue change throughout disease course. We aimed to determine associations between self-reported perceived fatigue and metabolic and clinical features of ALS, and perceived fatigue over the course of disease. Methods: This prospective study was conducted between July 2017 and March 2024. Baseline measures of self-reported perceived fatigue, metabolic rate, and clinical measures of disease were assessed in 117 participants with clinically definite or probable ALS. For comparison, fatigue and metabolic rate were collected from 107 control participants. Perceived fatigue was determined using the Fatigue Severity Scale (FSS). Metabolic rate was assessed using indirect calorimetry. Functional capacity and clinical progression were assessed using the ALS Functional Rating Scale-Revised (ALSFRS-R). Results: Baseline levels of perceived fatigue were greater in people living with ALS (plwALS) when compared to controls (5.44 vs. 2.55; p < 0.01). Perceived fatigue was higher in plwALS with lower ALSFRS-R scores and was not associated with measures of metabolism. For most plwALS, perceived fatigue remained high as functional capacity worsened. Conclusion: Our findings confirm higher prevalence of perceived fatigue in plwALS, with persistently high FSS scores reported by most patients during follow-up. High levels of fatigue were not associated with hypermetabolism, suggesting that metabolic rate is unlikely to be a primary contributor. Results highlight a need for further research to identify factors that contribute to fatigue in ALS, and options for improved fatigue management.

Treatments of fatigue after spinal cord injury: a systematic review and meta-analysis

STUDY DESIGN

Systematic Review and Meta-analysis.

SETTING

Canada.

OBJECTIVES

Fatigue is one of the most common consequences of spinal cord injury (SCI). In this systematic review and meta-analysis, we examined interventions for fatigue in SCI and evaluated their effectiveness.

METHODS

MEDLINE, EMBASE, CINAHL, and PsycINFO databases were searched up to January 2024 inclusive. Randomized controlled trials (RCTs) that assessed any intervention for at least one fatigue outcome in people with SCI were included. Study quality was assessed using the Cochrane Risk of Bias Tool.

RESULTS

Initial screening identified 282 studies from which six RCTs were included in the review (N = 249). One study found that moderate-intensity arm-crank exercise significantly improved fatigue compared to a control group (p = 0.036) with a large effect size (standard mean difference [SMD] = 1.05; 95% confidence interval [CI], 0.10-2.00). Two studies assessing behavioral interventions found a moderate effect on fatigue (SMD = 0.46; 95% CI, -0.00-0.92; p = 0.05). Two studies did not find an effect of massage therapy on fatigue (SMD = 0.06; 95% CI, -0.38-0.50; p = 0.80). The risk of bias was classified as High for all but two of the RCTs.

CONCLUSIONS

These findings suggest that exercise and behavioral interventions promoting an active lifestyle may have a positive effect on fatigue. More research with larger sample sizes, including controls for co-morbid conditions like pain and depression, is needed to establish evidence-based treatments for reducing fatigue in people with SCI.

Translation and Validation of the Portuguese Version of the Rating-of-Fatigue Scale

BACKGROUND

The Rating-of-Fatigue (ROF) scale is a validated tool to measure changes in perceived fatigue in sports and everyday contexts; thus, this study aimed to translate and validate the Portuguese version of the ROF scale. For this, the study was composed of three phases. Phase 1 involved a comprehensive translation of the ROF scale into Portuguese, followed by a back-translation and a consolidation process to obtain the final version of the ROF scale in Portuguese. In phase 2, the face validity of the scale was assessed. Seventy-three native Portuguese speakers responded to a series of Likert scale items designed to evaluate the purpose of the scale and assess whether it accurately measured the intended construct. In the final phase, the convergent and divergent validity of the scale was assessed during an incremental cycling test to exhaustion, followed by 10 min of passive recovery and a subsequent repetition of the initial 5 min of the test. The study was conducted between October 2023 and June 2024 in Portugal.

RESULTS

The results from phase 1 indicated a high level of comparability and interpretability between the original and back-translated versions, with only minor adjustments made to finalize the Portuguese version of the ROF scale. In phase 2, a high level of face validity was observed. The median score for the item "measures fatigue" was (median [IQR]) was 3.0 [3.0, 4.0] out of 4. After participants were provided with the scale instructions, the face validity score improved significantly (4.0 [3.0, 4.0]; p = 0.001). In phase 3, during the incremental test, very large correlations were observed between ROF, and key physiological and performance indicators, including rating of perceived exertion (RPE), heart rate, oxygen consumption, and power output. Discriminant validity between ROF and RPE was found during the recovery.

CONCLUSIONS

The present study indicates that the Portuguese version of the ROF maintains the properties of the original version and can be used effectively in the Portuguese language.

Mindfulness-based stress reduction as perceived by individuals with pathological mental fatigue after an acquired brain injury

After acquired brain injury (ABI), some individuals suffer from long-term fatigue and emotional distress, which affects their work ability and daily life. Mindfulness-based stress reduction (MBSR) has shown promising results in quantitative studies as a complementary treatment for pathological mental fatigue (PMF) after ABI. This study aims to explore how people suffering from lasting PMF after ABI experience MBSR in relation to their PMF, with the intention of better meeting the rehabilitation needs of those affected. Seven individuals (mean age 42 years) who had suffered from long-lasting PMF after ABI took part in the study. None of them had resumed work due to their PMF, but all had recovered from neurological impairments. They were interviewed after completing an MBSR course. Thematic analysis of the participants' perspectives suggested that the MBSR program provided them with coping techniques for living with PMF. They gained a deeper understanding of their condition becoming more self-compassionate, and the treatment provided them with a forum for meeting and sharing experiences with others with similar problems. The qualitative results strengthen the evidence for MBSR as a feasible psychoeducative complementary treatment for PMF after ABI.

Smartphone-based gait analysis in the assessment of fatigue and fatigability in people with multiple sclerosis: a supervised cohort study

BACKGROUND

Gait impairments and fatigue are the most common and disabling symptoms in people with multiple sclerosis (PwMS). Objective 6-min walk test (6MWT) gait testing can be improved through body-worn accelerometers, but its association to subjective fatigue and objective fatigability is contradictory. This study aims to validate an algorithm using smartphone sensor data for spatial-temporal gait parameters in PwMS and healthy controls, and evaluate its accuracy in detecting fatigability, and quantify its association with fatigue in PwMS.

METHODS

We recruited PwMS with mild to moderate disability (EDSS 0.0-6.5) and healthy controls in a supervised, lab-based cohort study. All participants performed the 6MWT while wearing a smartphone at the hip, which collected acceleration data of step count, cadence and walking speed. Algorithm validation included the mean absolute percentage error (MAPE) and Bland-Altman analysis. Fatigability and fatigue were measured in PwMS, with fatigability defined as a 10% decline in gait performance, and fatigue using the fatigue scale for motor and cognitive functions (FSMC). Further, correlations between gait parameters and FSMC were assessed.

RESULTS

A total of 38 PwMS and 24 healthy controls were included. The algorithm demonstrated high validity for step count (MAPE < 3%) and cadence (MAPE < 10%). Gait analyses revealed fatigability in between 2.6 and 15.8% of PwMS, with large differences between the gait parameter assessed. Significant correlations were found especially between FSMC motor fatigue scores and step count (r = - 0.50), cadence (r = 0.51) and walking speed (r = 0.50).

CONCLUSION

Smartphone-based gait analysis provides an accessible and valid method for detecting steps and cadence. There are major differences in the assessment of fatigability, but an allover association to subjective motor fatigue.

Adaptogens in Long-Lasting Brain Fatigue: An Insight from Systems Biology and Network Pharmacology

Long-lasting brain fatigue is a consequence of stroke or traumatic brain injury associated with emotional, psychological, and physical overload, distress in hypertension, atherosclerosis, viral infection, and aging-related chronic low-grade inflammatory disorders. The pathogenesis of brain fatigue is linked to disrupted neurotransmission, the glutamate-glutamine cycle imbalance, glucose metabolism, and ATP energy supply, which are associated with multiple molecular targets and signaling pathways in neuroendocrine-immune and blood circulation systems. Regeneration of damaged brain tissue is a long-lasting multistage process, including spontaneously regulating hypothalamus-pituitary (HPA) axis-controlled anabolic-catabolic homeostasis to recover harmonized sympathoadrenal system (SAS)-mediated function, brain energy supply, and deregulated gene expression in rehabilitation. The driving mechanism of spontaneous recovery and regeneration of brain tissue is a cross-talk of mediators of neuronal, microglia, immunocompetent, and endothelial cells collectively involved in neurogenesis and angiogenesis, which plant adaptogens can target. Adaptogens are small molecules of plant origin that increase the adaptability of cells and organisms to stress by interaction with the HPA axis and SAS of the stress system (neuroendocrine-immune and cardiovascular complex), targeting multiple mediators of adaptive GPCR signaling pathways. Two major groups of adaptogens comprise (i) phenolic phenethyl and phenylpropanoid derivatives and (ii) tetracyclic and pentacyclic glycosides, whose chemical structure can be distinguished as related correspondingly to (i) monoamine neurotransmitters of SAS (epinephrine, norepinephrine, and dopamine) and (ii) steroid hormones (cortisol, testosterone, and estradiol). In this narrative review, we discuss (i) the multitarget mechanism of integrated pharmacological activity of botanical adaptogens in stress overload, ischemic stroke, and long-lasting brain fatigue; (ii) the time-dependent dual response of physiological regulatory systems to adaptogens to support homeostasis in chronic stress and overload; and (iii) the dual dose-dependent reversal (hormetic) effect of botanical adaptogens. This narrative review shows that the adaptogenic concept cannot be reduced and rectified to the various effects of adaptogens on selected molecular targets or specific modes of action without estimating their interactions within the networks of mediators of the neuroendocrine-immune complex that, in turn, regulates other pharmacological systems (cardiovascular, gastrointestinal, reproductive systems) due to numerous intra- and extracellular communications and feedback regulations. These interactions result in polyvalent action and the pleiotropic pharmacological activity of adaptogens, which is essential for characterizing adaptogens as distinct types of botanicals. They trigger the defense adaptive stress response that leads to the extension of the limits of resilience to overload, inducing brain fatigue and mental disorders. For the first time, this review justifies the neurogenesis potential of adaptogens, particularly the botanical hybrid preparation (BHP) of Arctic Root and Ashwagandha, providing a rationale for potential use in individuals experiencing long-lasting brain fatigue. The review provided insight into future research on the network pharmacology of adaptogens in preventing and rehabilitating long-lasting brain fatigue following stroke, trauma, and viral infections.

Exploring rest advice in fatigue interventions in rehabilitation among adults with long-term conditions: a systematic scoping review of the reporting of rest in randomised controlled trials

OBJECTIVE

To explore how rest is described or included as part of rest advice in fatigue interventions within rehabilitation for adults with Long-term conditions (LTC).

DATA SOURCES

This scoping review identified fatigue interventions through PubMed, the Cumulative Index to Nursing and Allied Health Literature, the Allied and Complementary Medicine Database, and the Physiotherapy Evidence Database, from inception to July 2024.

STUDY SELECTION

Two independent reviewers screened and selected the articles. Studies were included if they: (1) involved adults with LTC, (2) used non-pharmacological fatigue interventions, (3) had fatigue as the primary outcome, and (4) were randomised controlled trials (5). Only randomised controlled trials that include rest advice in the interventions were selected.

DATA EXTRACTION

Extracted data included the first author's name, year of publication, country, type of LTC, intervention category, specific interventions, how rest was reported in all interventions. Furthermore, rest was reported using the FITT principle, focusing on the frequency, intensity, duration, and type of rest in the exercise interventions and key conclusions.

DATA SYNTHESIS

Results were summarised, tabulated, and reported descriptively. Out of 13,645 initial records, 56 studies were included in the review. Of the total interventions analysed, 55.4% (31/56) were classified as physical activity interventions, 14.3% (8/56) as psychological interventions (e.g., cognitive behavioural therapy), 12.5% (7/56) were identified as energy management strategies, 8.9% (5/56) as educational interventions, and 8.9% (5/56) as activity pacing strategies. A disparity was observed in the instruction of rest advice between exercise interventions and daily fatigue management strategies. Specifically, physical activity interventions tended to adopt a more prescriptive approach to rest, whereas rest in daily fatigue management strategies was primarily instructed through education on the importance of rest in daily life. Notably, the level of detail provided in reporting rest parameters was generally limited.

CONCLUSIONS

This review found insufficient reporting of rest, highlighting a significant gap and indicating the need for improved documentation and standardisation of rest in fatigue interventions. Future research is necessary to better understand the role of rest in the rehabilitation of LTC.

Post-stroke fatigue - a multidimensional problem or a cluster of disorders? A case for phenotyping post-stroke fatigue

Post-stroke fatigue is a chronic problem with significant impact on morbidity and mortality, which urgently needs effective treatments. The last decade has seen a considerable increase in interest in understanding the pathophysiology of fatigue and developing treatments. In this review, following a summary of theoretical frameworks to understand chronic fatigue, I make a case for why phenotyping fatigue is a necessary step to fully understand pathophysiology, which in turn is essential for the development of robust treatments. I then appraise current post-stroke fatigue literature with the view of identifying post-stroke fatigue phenotypes.

From "invisible" to "audible": Features extracted during simple speech tasks classify patient-reported fatigue in multiple sclerosis

BACKGROUND

Fatigue is a major "invisible" symptom in people with multiple sclerosis (PwMS), which may affect speech. Automated speech analysis is an objective, rapid tool to capture digital speech biomarkers linked to functional outcomes.

OBJECTIVE

To use automated speech analysis to assess multiple sclerosis (MS) fatigue metrics.

METHODS

Eighty-four PwMS completed scripted and spontaneous speech tasks; fatigue was assessed with Modified Fatigue Impact Scale (MFIS). Speech was processed using an automated speech analysis pipeline (ki elements: SIGMA speech processing library) to transcribe speech and extract features. Regression models assessed associations between speech features and fatigue and validated in a separate set of 30 participants.

RESULTS

Cohort characteristics were as follows: mean age 49.8 (standard deviation (SD) = 13.6), 71.4% female, 85% relapsing-onset, median Expanded Disability Status Scale (EDSS) 2.5 (range: 0-6.5), mean MFIS 27.6 (SD = 19.4), and 30% with MFIS > 38. MFIS moderately correlated with pitch (R = 0.32, p = 0.005), pause duration (R = 0.33, p = 0.007), and utterance duration (R = 0.31, p = 0.0111). A logistic model using speech features from multiple tasks accurately classified MFIS in training (area under the curve (AUC) = 0.95, R2 = 0.59, p < 0.001) and test sets (AUC = 0.93, R2 = 0.54, p = 0.0222). Adjusting for EDSS, processing speed, and depression in sensitivity analyses did not impact model accuracy.

CONCLUSION

Fatigue may be assessed using simple, low-burden speech tasks that correlate with gold-standard subjective fatigue measures.

Coping is a moderator of relationships between cognitive fatigue and cognitive variability in multiple sclerosis

OBJECTIVE

Mean levels of cognitive functioning typically do not show an association with self-reported cognitive fatigue in persons with multiple sclerosis (PwMS), but some studies indicate that cognitive variability has an association with cognitive fatigue. Additionally, coping has been shown to be a powerful moderator of some outcomes in multiple sclerosis (MS). To date, however, coping has not been considered as a possible moderator of the relationship between cognitive fatigue and cognitive variability in MS. The current study examined this relationship.

METHOD

We examined 52 PwMS. All participants were administered the Fatigue Impact Scale, the Coping Orientation to Problems Experienced Questionnaire, and cognitive tests. Indices of variability for memory and attention/executive functioning tests were used as outcome variables. Avoidant coping, active coping, and composite coping indices were used as moderators.

RESULTS

The interaction analyses for the avoidant coping and composite coping indices were significant and accounted for 8 and 11% of the attention/executive functioning variability outcome, respectively. The interactions revealed that at low levels of cognitive fatigue, attention/executive functioning variability was comparable between the low and high avoidant and composite coping groups. However, at high levels of cognitive fatigue, PwMS using lower levels of avoidant coping (less maladaptive coping) showed less variable attention/executive functioning scores compared with those using higher levels of avoidant coping. We found a similar pattern for the composite coping groups.

CONCLUSION

At high levels of cognitive fatigue, PwMS using adaptive coping showed less attention/executive functioning variability. These findings should be considered in the context of treatment implications.

Dual-Task Resistance Training Improves Strength and Reduces Pain More Than Resistance Exercise Alone in Elbow Fracture Rehabilitation: A Randomized Controlled Trial

OBJECTIVE

To examine the effects on strength, pain intensity, range of motion (ROM), and functionality of a 12-week dual-task resistance exercise program in patients undergoing rehabilitation from elbow fractures.

DESIGN

Randomized controlled trial.

SETTING

Rehabilitation hospital.

PARTICIPANTS

Individuals undergoing elbow fracture rehabilitation (N=32).

INTERVENTION

Randomization was performed sequentially using numbered envelopes containing assignments to either an intervention group (dual-task resistance training using a mathematical task with self-regulation, N=18) or a control group (traditional resistance training, N=14) for 12 weeks.

MAIN OUTCOME MEASURES

The primary outcomes were muscle strength for elbow flexors and extensors and pain assessed by the visual analog scale from 0 to 100 mm. The secondary outcomes were kinesiophobia assessed by the Tampa Scale-11 and disability using the Disabilities of the Arm, Shoulder, and Hand questionnaire and passive ROM.

RESULTS

Dual-task resistance training improved strength and reduced pain more than resistance training alone (P<.05), and only the dual-task group improved in kinesiophobia (P<.05). The linear regression showed a significant negative association between kinesiophobia and increased elbow strength in the dual-task group (flexion, r=-0.53, P=.024; extension, r=-0.65, P=.004) but not in the control group (P>.05). No significant differences were observed between the group for disability and passive ROM (P>.05).

CONCLUSIONS

Dual-task resistance training and traditional resistance training both enhance strength, reduce pain, improve functionality, and increase ROM after 12 weeks of elbow fracture rehabilitation. However, dual-task resistance training is superior to resistance training alone in enhancing strength and reducing pain.

Age-specific effects of a sustained cognitive activity on perceived cognitive fatigue as well as single- and dual-task treadmill walking performance

During their daily lives humans are often confronted with sustained cognitive activities (SCA) leading to state fatigue, a psychobiological state characterized by a decrease in cognitive and/or motor performance and/or an increase in perception of fatigue. It was recently shown that performing SCA can impair overground dual-task gait performance in older adults, but it is currently unknown whether there is a task- and/or age-specific modulation in gait performance during treadmill walking. Therefore, the effect of a SCA on single- and dual-task treadmill walking performance was investigated in young and old adults. Using a crossover design, spatio-temporal gait parameters of 24 young and 23 older healthy participants were measured using motion capturing during single- and dual-task (including three cognitive interference tasks: word list generation, arithmetic, and Stroop-task) treadmill walking before and after SCA (30 min Stroop-task) and a control task (reading). Moreover, cognitive fatigue, wakefulness, mood, and arousal were assessed. Although the SCA induced age-specific perceptual responses, no difference was found for cognitive performance during the Stroop-task. The cognitive interference task performance (word list generation, arithmetic, and Stroop-task) during walking on the treadmill did not decrease after the SCA. Single- and dual-task gait performance (e. g., step width and step length) specifically changed after the SCA and after the reading control task in both groups. Data indicate that perceived cognitive fatigue has an impact on single- and dual-task treadmill walking performance, with task- and age-specific differences. Although no general age-specific changes in single- and dual task gait performance following SCA were identified, perceived cognitive fatigue should be considered as an intrinsic risk factor for falls.

Effect of fatigability on sprint time performance and force-velocity profile according to maturity status in young rugby players

Little is known about the influence of fatigue in repeated overground sprinting on force-velocity properties in children and adolescents, while this ability to repeat sprints is important for future progress in rugby union. Sprint time decline is commonly used to assess fatigability. However, it does not provide data on biomechanical aspects of sprint performance such as maximal power, force, and velocity production. As sprint time performance and force-velocity properties do not linearly change during adolescence, considering maturity status is important. This study aimed to assess the effect of fatigue on sprint time performance fatigability, force-velocity parameters, and mechanical effectiveness according to maturity status. A group of fifteen boys (12.5 ± 0.5 years) children and a group of seventeen boys (15.1 ± 0.6 years) adolescent rugby players completed seven blocks, consisting of a 30-meter sprint followed by five minutes of high-intensity exercise with one minute of passive recovery. The force-velocity parameters were calculated at each sprint, and performance decrement was assessed using a fatigue index. A main effect of block repetition was found for maximal power output, maximal force, maximal velocity, 30-meter sprint time, fatigue index and mechanical effectiveness parameters with large effect sizes (p <0.001; [Formula: see text] = 0.19 to 0.47) and without a main effect of maturity status (p = 0.37 to 0.99; [Formula: see text] = 0.00 to 0.05). This could be explained by the modalities (duration, intensity, recovery) of the protocol and the training level of the adolescent group. For both groups, the decrease in maximal power output was due more to a reduction in maximal velocity than force, and mechanical effectiveness was negatively impacted. Coaches could prioritize the training of horizontal force at high velocity under fatigue conditions, as this ability tends to be the most affected. They could also incorporate training on mechanical effectiveness as this is a determinant in team sports.

Does muscle fatigue change motor synergies at different levels of neuromotor control?

We investigated the effects of static and dynamic fatigue on motor synergies, focusing on their hierarchical control. Specifically, we examined whether changes in fatigue influence the central nervous system's ability to preserve movement stability. In addition to exploring the direct impact of fatigue on motor synergies, we also analyzed its effects at two distinct levels of hierarchical control, aiming to elucidate the mechanisms by which fatigue alters motor coordination and stability. Thirteen healthy, young and right-handed male participants took part in the study. Participants performed a bilateral accurate force production task under static and dynamic fatigue conditions at 30% of maximal voluntary contraction level with elbow flexors. Muscle activity level were collected from five muscles of each limb: biceps brachii, brachialis, brachioradialis, flexor carpi radialis, and flexor carpi ulnaris. The results revealed distinct effects of fatigue on isometric force production in the elbow joint tasks. On the higher level of hierarchy control of synergies, there were non-significant effects of different types of fatigue on movement performance, however, on the lower level we observed a strong effect of fatigue on forming motor synergies. There was no significant difference between the type of applied fatigue protocol on force and muscle activity data, nevertheless, the contribution of involved muscles to the task has changed. Our findings indicate that the central nervous system employs specific strategies to counteract fatigue and preserve movement stability during performance. However, the precise mechanisms by which variability at lower levels of hierarchical control influence higher levels remain unclear, highlighting a critical gap in our understanding of motor coordination under fatigue. Future studies should explore how these interactions across hierarchical levels contribute to movement stability under different fatigue conditions.

Association of real life postural transitions kinematics with fatigue in neurodegenerative and immune diseases

Fatigue is prevalent in immune-mediated inflammatory and neurodegenerative diseases, yet its assessment relies largely on patient-reported outcomes, which capture perception but not fluctuations over time. Wearable sensors, like inertial measurement units (IMUs), offer a way to monitor daily activities and evaluate functional capacity. This study investigates the relationship between sit-to-stand and stand-to-sit transitions and self-reported physical and mental fatigue in participants with Parkinson's, Huntington's, rheumatoid arthritis, systemic lupus erythematosus, primary Sjögren's syndrome and inflammatory bowel disease. Over 4 weeks, participants wore an IMU and reported fatigue levels four times daily. Using mixed-effects models, associations were identified between fatigue and specific kinematic features, such as 5th and 95th percentiles of sit-to-stand performance, suggesting that fatigue alters the control and effort of movement. These kinematic features show promise as indicators for fatigue in these patient populations.

Development of the SMA EFFORT: A new approach to characterize perceived physical fatigability in spinal muscular atrophy

BACKGROUND

Fatigue and fatigability are commonly reported in spinal muscular atrophy (SMA). Physical fatigability, proposed to be the most relevant to SMA pathophysiology, encompasses performance-based and perceived physical fatigability (PPF) assessments. While performance-based measures have highlighted physical fatigability as an SMA hallmark, PPF is not well characterized due to the lack of disease- and construct-specific scales.

OBJECTIVE

Our aim was to create a patient-reported outcome measure tailored for SMA, named the SMA EFFORT, to improve PPF assessment. Here, we describe the scale development process, assess scale properties, and discuss future research and application.

METHODS

SMA and scale development experts organized a comprehensive physical activity item bank, relevant across the SMA phenotypic spectrum. Activities were systematically categorized by varying intensities and durations. The SMA EFFORT was completed by an international cohort of individuals with all types of SMA. To compare PPF across demographic and clinical variables, SMA EFFORT PPF percent (PPF%) composite scoring was established.

RESULTS

One hundred eighteen participants completed the SMA EFFORT. Total PPF% scores were broadly distributed within functional groups, with differences between non-sitters (35.1 ± 21.0) and sitters (24.9 ± 15.1) (p = 0.006), and those with (34.4 ± 18.1) and without respiratory support (26.4 ± 17.8) (p = 0.02). Participants treated with disease modifying therapy (DMT) showed similar scores to those without treatment (p = 0.70). Further, no differences in scores were observed in participants with scoliosis surgery and those without (p = 0.71). Subscale analyses revealed differences in mean PPF% subscale scores by functional group.

CONCLUSIONS

The novel SMA EFFORT standardizes PPF ratings by anchoring activity to intensity and duration. Item and scale data insights will inform the next iteration, which will undergo additional investigation. The SMA EFFORT aims to improve upon current measures to better assess treatment impact on physical well-being across the SMA spectrum.

The role of fatigue in attentional processing in multiple sclerosis: data from event-related potentials

Fatigue is an extremely common symptom in in people with multiple sclerosis (PwMS) and has a severe impact on quality of life. The purpose of the present study was to verify whether fatigue in PwMS is associated with a selective covert attention impairment, as measured by event-related potentials and to assess whether it is more associated with an impairment of top-down or bottom-up attentional control. Twenty-two PwMS and fatigue-MSF, 17 without fatigue-MSnF and 35 healthy volunteers underwent a three-stimulus P300 novelty task that elicits both the P3a and the P3b components. P3b latency was comparable between groups, but PwMS, independently from the presence of fatigue displayed significantly greater P3b amplitudes. P3a latency was significantly prolonged in MSF alone, while P3a amplitude in MSnF group was greater than controls. MSF were able to categorize the task-relevant target stimulus but the orienting response to a novel salient stimulus was delayed, indicating an impairment in bottom-up attentional control mechanism related to ventral attention network. Fatigue is selectively associated with a covert attentional deficit related to the ability to reallocate attentional resources to salient stimuli, a crucial function of adaptive decision-making behaviour.

The effects of chronic fatigue and chronic stress on alterations in immune cell responses to acute psychosocial stress

Fatigue is a common and debilitating symptom of a broad spectrum of diseases. Previous research has shown that individuals suffering from chronic forms of fatigue experience significantly more stress compared to healthy individuals, suggesting that stress is a potential pathophysiological factor in the onset and maintenance of chronic fatigue. Individually, chronic experiences of fatigue and stress have been associated with disruptions in adaptive immunity. However, how chronic fatigue and chronic stress together affect immune regulation is not fully understood. Here, we investigated the unique and combined contribution of chronic fatigue and chronic stress on immune cell redistribution in response to, and recovery from, acute psychosocial stress. Eighty women with high or low levels of chronic fatigue and varying levels of chronic stress were exposed to a psychosocial laboratory stressor. Blood samples were collected 10 min before and then at 10, 40, and 100 min after the end of stress. The main lymphocyte subpopulations (CD3+, CD3 + CD4+, CD3 + CD8+, CD16 + CD56+, and CD19 + cells) were enumerated via flow cytometry. Acute stress resulted in an increase in CD8 + and CD16+/CD56 + cells, a decline in CD4 + cells, and no effects on CD19 + B lymphocytes. Importantly, the magnitude of immune cell redistribution during stress reactivity (CD3+, CD4+, CD16+/CD56 + ) and recovery (CD3 + ) was contingent on fatigue and chronic stress levels of individuals. Notably, in contrast to low-fatigued individuals, who showed steeper changes in cell populations, increasing levels of chronic stress did not impact immune cell migration responses in high-fatigued individuals. Our findings demonstrate the compounded blunting effects of fatigue and chronic stress on adaptive immune functioning, highlighting a potential pathway for vulnerability and detrimental effects on long-term health.

Longitudinal relationships between free-living activities, fatigue, and symptom severity in myasthenia gravis using cohort and individualized models

INTRODUCTION/AIMS

Fluctuating symptoms and fatigue are common issues in myasthenia gravis (MG), but it is unclear if these symptoms are related to physical activity or sleep patterns. This study sought to determine the day-to-day relationship between patient-reported symptoms and physical activity and sleep over 12 weeks.

METHODS

Sixteen participants with generalized MG wore a wrist-mounted accelerometer continuously for the study duration and reported their symptoms and fatigue each evening. Cumulative link mixed models were used to analyze whether clinical and demographic characteristics, physical activity, and sleep were related to symptom severity and fatigue over the study period. Three types of models were constructed: a cohort model, a model in which data was scaled to each participant, and individual models.

RESULTS

The cohort model indicated that higher disease severity, female sex, more comorbidities, less physical activity, more inactive time, and lower quantity of sleep were significantly associated with increased symptom severity and fatigue (p < .05). However, in the within-participant scaled model, there were almost no significant associations with physical activity or sleep. In the individual models, some participants showed similar results to the cohort model, but others showed no associations or the opposite response in some variables.

DISCUSSION

While physical activity and sleep were associated with self-reported symptoms and fatigue within this population, this was not necessarily applicable to individuals. This demonstrates the importance of an individualized analysis for determining how physical activity and sleep may impact outcomes in MG, with implications for clinical and self-management.

Interaction between the leg recovery test and subjective measures of fatigue in handball players: short-, mid-, and long-term assessment

Background

The physical and mental demands of handball during training or competition often lead to fatigue which can impair performance. Many attempts have been made to assess the level of fatigue in athletes either by objective (neuromuscular performance) or subjective (questionnaires) measures, however, their interplay over short-, mid-, and long-term periods is currently unknown. Knowledge about both types of assessments is important as load management by coaches is traditionally based on direct adjustments following a training session, adjustments of content structure of training weeks between games, as well as adjustments of load management over the entire competitive season. Thus, this study aimed to investigate the interplay between objective and subjective fatigue measures at multiple test times throughout a handball season.

Methods

A total of 100 highly trained (Tier level 3) adolescent or young adult team handball players (23 females) took part in the study. The parameters tested were the Leg Recovery Test (LRT score) which is based on the countermovement jump height (CMJ) and was assessed by a commercial wristwatch (Polar Vantage V2) as an objective measure of neuromuscular fatigue. Additionally, on a subjective level, questionnaire-based athlete self-report measures, specifically the Perceived Recovery Status Scale (PRSS) and the Short Scale of Recovery and Strain (KEB) were assessed. We used non-parametric tests to detect differences between relevant test time points (short-term: immediately following one handball-specific training session, i.e., from T0 to T1; mid-term: over the course of three consecutive training days, i.e., from T0 to T2; long-term: over the course of 8 months of training, i.e., from T0 to T12) and linear mixed models to evaluate the interplay between objective (LRT score) and subjective (KEB score and PRSS score) measures of fatigue across one season.

Results

Non-parametric tests showed that CMJ height (p = .012) and the KEB (p < .001) were higher at T1 compared to T0 for the short-term assessment. Over the course of three consecutive training days (i.e., mid-term assessment), the CMJ height score decreased (T0 to T2: p < .001; T1 to T2: p = .018) and the PRSS score (T0 to T2: p < .001; T1 to T2: p = .003) increased. Linear mixed models revealed no significant effects of KEB or PRSS score on LRT score (i.e., CMJ height) for the short- and mid-term assessments. In terms of the long-term assessments, we detected no general direct or interaction effects of PRSS score, workload, and test time point on LRT score, except for an interaction between PRSS score and workload on LRT score (p = .032), which indicates a workload-dependent association between PRSS and the objective fatigue measure (LRT score).

Conclusion

Athlete self-reported measures of fatigue indicated significantly higher cumulative fatigue after both short- and mid-term periods, whereas this increase was observed in the LRT score only during the mid-term period. Furthermore, the absence of a relationship between the objective and subjective measures of fatigue during short- and mid-term periods suggests that these measures assess distinct types of fatigue. In the long-term assessments, the significant interaction between the PRSS score and workload on the LRT score suggests that higher workloads are associated with an increased correlation between subjective (PRSS score) and objective (LRT score) measures of fatigue. This indicates that perceived fatigue may be a more sensitive indicator of fatigue, which can be managed to maintain high levels of neuromuscular performance (LRT score). However, with higher workloads (>10 h per week), associations between the objective and subjective measures become apparent, suggesting that workload serves as a common factor influencing overall fatigue.

Cross-cultural translation, validation, and responsiveness of the Pittsburgh Fatigability Scale - Italian version (PFS-I) in a mixed-sample of older adults

INTRODUCTION

Older adults experience fatigue which impacts health-related quality of life. The Pittsburgh Fatigability Scale (PFS) was specifically designed to assess perceived physical and mental fatigability in older adults. The aim of this study was to translate the PFS into Italian (PFS-I) and to investigate its psychometric properties.

METHODS

The PFS-I was translated in accordance with international standards. The following properties were evaluated: structural validity, internal consistency, hypotheses testing for construct validity, test-retest reliability using intraclass correlation coefficients (ICC), and minimal clinically important difference (MCID) for responsiveness.

RESULTS

The study included 87 older adults with cardiovascular/respiratory diseases (CVRD), 46 with Parkinson disease (PD), and 67 healthy controls (HC). The PFS-I Physical and Mental subscales scores were significantly different in these populations, with HC reporting the lowest fatigability. Exploratory and confirmatory factor analysis showed a two-factor structure for both subscales, with good internal consistency (Cronbach's alpha: 0.86 and 0.89, respectively). The PFS-I Physical subscale showed weak goodness-of-fit of the confirmatory factor analysis models, whereas the PFS-I Mental subscale was deemed acceptable. Construct validity of the PFS-I was excellent with 75% (18 out of 24) of hypotheses accepted. Test-retest reliability was analyzed in a subset of 23 patients with CVRD and showed excellent results for both the PFS-I Physical and Mental subscales (ICC = 0.93 and 0.92, respectively). MCID ranged between 6 and 7 points for the Physical and 7-9 points for the Mental subscale.

CONCLUSIONS

The PFS-I is a valid, reliable, and responsive instrument to assess perceived fatigability for healthy older adults as well as those with CRVD and PD.

Effects of a symptom-titrated exercise program on fatigue and quality of life in people with post-COVID condition - a randomized controlled trial

Fatigue is the most prevalent symptom within the post-COVID condition (PCC). Furthermore, many patients suffer from decreased physical performance capacity and post-exertional malaise. Although exercise has been proposed as an effective therapeutic strategy for PCC, there is limited evidence on individualised and symptom-titrated exercise interventions in patients with fatigue and PEM. Therefore, we conducted a multi-centre randomised controlled trial to investigate the effectiveness of an individualised and symptom-titrated exercise program. We measured fatigue, health-related quality of life, hand-grip strength, endurance capacity and PEM before and after the 10-week intervention. A total of 118 individuals with PCC were included in the final intention-to-treat analysis. All tests and training sessions took place in commercial fitness and health facilities. We found significant effects on fatigue severity, health-related quality of life and physical performance capacity. Adjusting the individual exercise load to daily fatigue has proven to be an effective and safe strategy in PCC patients with fatigue. Under the guidance of qualified professionals and by utilising symptom-titrated training recommendations, commercial fitness and health facilities present an appropriate setting for outpatient exercise rehabilitation in PCC.

Defining and measuring long COVID fatigue: a scoping review

OBJECTIVE

Long COVID encompasses a range of symptoms in which fatigue is one of the most prevalents. It is clear from other conditions that the definition and measurement of fatigue can be complex, but it is not clear how fatigue is defined and measured in long COVID. To advance our understanding, this review summarises the definitions and measures of long COVID fatigue being used by researchers.

DESIGN

Scoping review following JBI methodology and reports using the Preferred Reporting Items for Systematic Reviews and Meta-analyses extension for scoping reviews.

DATA SOURCES

Medline, Scopus, CINAHL, PsycINFO, EMCARE, Web of Science, Epistemonikos, Cochrane Central Register of Controlled Trials, Dimensions, Overton and ProQuest Dissertation & Theses Database were searched from January 2020 to May 2023.

ELIGIBILITY CRITERIA

This review included quantitative and qualitative studies that included any definition of long COVID and/or measurement tool that purported to quantify either the impact, severity or symptoms of long COVID fatigue.

DATA EXTRACTION AND SYNTHESIS

Two independent reviewers screened the title, abstracts and full texts of the selected studies based on the inclusion criteria. Data extraction was performed by two independent reviewers. The data were summarised in tabular format and a narrative summary.

RESULTS

The search retrieved 9839 studies, of which 57 met the inclusion criteria. Only 21 (37%) provided a definition of fatigue. Definitions ranged across physical, mental, cognitive, emotional, psychosocial, central, peripheral, postexertional symptom exacerbation and general dimensions of fatigue. Fifty-five (96%) used a measurement or assessment of fatigue. Twenty-six measures of fatigue were identified: 21 self-report measures (eg, Fatigue Assessment Scale) and five fatigability measures that purport to reflect changes in physiological processes that contribute to or reflect fatigue (eg, change in force generating capacity of a muscle).

CONCLUSIONS

The definitions identified demonstrate considerable diversity, each highlighting different dimensions of long COVID fatigue. Long COVID fatigue was predominantly measured through self-report methods, which were problematic. There is an urgent need to better understand long COVID fatigue and to identify the different mechanisms involved. In order to do this, we need consistency with the language around fatigue and its measurement within research and across disciplines.

REVIEW REGISTRATION

The protocol has been registered on open science framework (https://doi.org/10.17605/OSF.IO/HNF8Z).

[Fatigue and sensorimotor instability : Neurologically controlled conversion of post-COVID-19 patients]

BACKGROUND

For the treatment of the symptoms of post-COVID-19 syndrome, no causal therapy is currently widely recommended according to evidence-based criteria. The overarching goal of the intervention study over a 3-year period (Q1-2021-Q4-2023) was to evaluate the changes in the key symptoms of fatigue and sensorimotor instability through individualized stress-controlled training therapy and through intensified cognitive behavioral therapy.

MATERIAL AND METHODS

In the 3‑year period 407 vaccinated nucleocapsid positive patients were treated at the Post-COVID-19 Center Lausitz (Senftenberg). In 78 (around 19%) fatigue/immunometabolic depression and sensorimotor instability were identified as the leading syndromes. The evaluation of the individualized stress-controlled training therapy was based on the specific post-COVID-19 syndrome and motor fatigue parameters. The secondary psychosomatic syndrome was assessed using cognitive fatigue parameters and cognitive behavioral therapy instruments. The investigation of -parameters influencing behavior took place in Q2-2023-Q4-2023 with a guide-supported qualitative interview among the participants.

RESULTS

The post-COVID-19 key symptoms "fatigue," "sensorimotor instability," "neuropsychiatric symptoms," "cardiac/autonomic dysfunction," and "pain" improved significantly in the overall cohort and in the gender-specific analysis. A deterioration occurred in "secondary psychosomatic symptoms". A therapeutic effect was demonstrated for all motor fatigue parameters for the entire cohort using the Cohen's d value. An intensification of cognitive behavioral therapy achieved positive effects through an increasing development of the patients' own activity and their self-control using persuasion and gamification.

Muscle contractile properties and perceived fatigue in the general and diseased population

Knowledge of muscle contractile properties, physical fitness, and their associations with perceived fatigue may provide insights into mechanisms inducing fatigue and treatment targets. We aimed to identify differences in contractile properties and physical fitness between populations, and examine associations with perceived fatigue. We pooled data on perceived fatigue, physical fitness, and contractile properties from six studies, including a control group (n = 90), cancer survivors (n = 27), patients with chronic obstructive pulmonary disease (COPD; n = 16), chronic myeloid leukemia (CML; n = 20), and statin users (n = 64). We evaluated differences between populations, and associations of contractile properties and physical fitness with perceived fatigue. Compared with the control group, we found differences in contractile properties of patients with COPD (larger muscle force decline: β = -10.5%, 95% CI = -16.7; -4.2, increase in early relaxation time (Rt): β = 84.4%, 95% CI = 51.7; 117.0, increase in half Rt: β = 83.1%, 95% CI = 45.5; 120.7, muscle force rise (MFR): β = 0.2%/ms, 95% CI = 0.1; 0.3, and decrease in MFR: β = -24.3%, 95% CI = -35.7; -13.0) and statin users (early Rt: β = -5.4 ms, 95% CI = -10.0; -0.8, increase in early Rt: β = 19.8%, 95% CI = 2.5; 37.1). Associations between contractile properties and perceived fatigue varied across populations. Longer relaxation times were associated with higher perceived fatigue in hemato-oncological populations. To conclude, contractile properties were impaired in patients with COPD and statin users. Associations between contractile properties and perceived fatigue varied across populations. In hemato-oncological populations, impaired muscle relaxation was associated with higher perceived fatigue.

Dynamic causal modelling highlights the importance of decreased self-inhibition of the sensorimotor cortex in motor fatigability

Motor fatigability emerges when challenging motor tasks must be maintained over an extended period of time. It is frequently observed in everyday life and affects patients as well as healthy individuals. Motor fatigability can be measured using simple tasks like finger tapping at maximum speed for 30 s. This typically results in a rapid decrease of tapping frequency, a phenomenon called motor slowing. In a previous study (Bächinger et al, eLife, 8 (September), https://doi.org/10.7554/eLife.46750 , 2019), we showed that motor slowing goes hand in hand with a gradual increase in blood oxygen level dependent signal in the primary sensorimotor cortex (SM1), supplementary motor area (SMA), and dorsal premotor cortex (PMd). It is unclear what drives the activity increase in SM1 caused by motor slowing and whether motor fatigability affects the dynamic interactions between SM1, SMA, and PMd. Here, we performed dynamic causal modelling (DCM) on data of 24 healthy young participants collected during functional magnetic resonance imaging to answer this question. The regions of interest (ROI) were defined based on the peak activation within SM1, SMA, and PMd. The model space consisted of bilateral connections between all ROI, with intrinsic self-modulation as inhibitory, and driving inputs set to premotor areas. Our findings revealed that motor slowing was associated with a significant reduction in SM1 self-inhibition, as uncovered by testing the maximum à posteriori against 0 (t(23)=-4.51, p < 0.001). Additionally, the model revealed a significant decrease in the driving input to premotor areas (t(23) > 2.71, p < 0.05) suggesting that structures other than cortical motor areas may contribute to motor fatigability.