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

Testing the predictive capacity of a muscle fatigue model on electrically stimulated adductor pollicis

PURPOSE

Based on the critical power (Pc or critical force; Fc) concept, a recent mathematical model formalised the proportional link between the decrease in maximal capacities during fatiguing exercises and the amount of impulse accumulated above Fc. This study aimed to provide experimental support to this mathematical model of muscle fatigability in the severe domain through testing (i) the model identifiability using non-exhausting tests and (ii) the model ability to predict time to exhaustion (tlim) and maximal force (Fmax) decrease.

METHODS

The model was tested on eight participants using electrically stimulated adductor pollicis muscle force. The Fmax was recorded every 15 s for all tests, including five constant tests to estimate the initial maximal force (Fi), Fc, and a time constant (τ). The model's parameters were used to compare the predicted and observed tlim values of the incremental ramp test and Fmax(t) of the sine test.

RESULTS

The results showed that the model accurately estimated Fi, Fc, and τ (CI95% = 2.7%Fi and 9.1 s for Fc and τ, respectively; median adjusted r2 = 0.96) and predicted tlim and Fmax with low systematic and random errors (11 ± 20% and - 1.8 ± 7.7%Fi, respectively).

CONCLUSION

This study revealed the potential applications of a novel mathematical formalisation that encompasses previous research on the critical power concept. The results indicated that the model's parameters can be determined from non-exhaustive tests, as long as maximal capacities are regularly assessed. With these parameters, the evolution of maximal capacities (i.e. fatigability) at any point during a known exercise and the time to exhaustion can be accurately predicted.

Assessing the Effect of Fatigue on Swallowing Function in Adults with Acute Stroke. A Pilot Study

Objective

To determine if fatigue systematically effects the timing of swallowing events and to discuss underlying causes of fatigue other than peripheral neuromuscular fatigue.

Design

Pre-post within-subject repeated-measures design.

Setting

General acute care hospital and designated stroke center.

Participants

Thirteen patients (10 males and 3 females) aged 52-80 years (mean 64.84±9.58 y) with acute stroke and clinically suspected dysphagia.

Interventions

Under videofluoroscopy, each participant swallowed a pre- and post-study 1-mL liquid barium bolus and, in an attempt to fatigue the system, 30-45 additional bolus trials of varying amounts (ie, 5 mL, 10 mL, and bite-sized) and consistencies (ie, International Dysphagia Diet Standardisation Initiative Level 0-7).

Main Outcome Measures

Six temporal sequences (ie, oral, pharyngeal, and pharyngeal delay transit times and durations of laryngeal vestibule closure, cricopharyngeal opening, and laryngeal elevation) for 1-mL liquid boluses were measured pre- and postvideofluoroscopic swallowing study and compared.

Results

Findings indicated that only 2 of the 6 temporal factors yielded significant differences pre- to post fatigue. The postvideofluoroscopic 1-mL liquid swallow took longer than the pre-videofluoroscopic 1-mL liquid swallow in terms of pharyngeal transit (1,11=5.362, P=.046) and pharyngeal delay time (F 1,11=5.228, P=.048).

Conclusions

These findings indicate that peripheral neuromuscular fatigue is unlikely to be the primary cause of the observed changes, as only 2 of the 6 temporal measures-pharyngeal transit time and pharyngeal delay time-were affected. In cases of peripheral neuromuscular fatigue, one would expect increases across all 6 timing measures due to the integrated nature of the swallowing process. Instead, the results suggest that the inconsistencies may stem from a delayed excitatory response of neurons or a delay in synaptic transmission within the nucleus tractus solitarius, potentially associated with stroke. This delay likely contributes to the prolongation of both pharyngeal transit and pharyngeal delay times. Thus, a model focused solely on peripheral neuromuscular fatigue does not fully account for the findings, highlighting the importance of considering central neural mechanisms in the clinical evaluation of swallowing disorders.

Performance fatigability in adults with spinal muscular atrophy treated long-term with nusinersen

INTRODUCTION/AIMS

Persons with spinal muscular atrophy (pwSMA) report progressive muscle weakness but also reduced endurance when performing repetitive tasks in daily life, referred to as "performance fatigability" (PF). Data regarding the effects of the new disease-modifying drugs on PF are scarce. Thus, our main objective was to examine PF in adult ambulatory pwSMA treated long-term with nusinersen.

METHODS

Six-minute walk test (6MWT) data from 14 adult pwSMA treated with nusinersen for up to 70 months were retrospectively analyzed to determine PF. Performance fatigability was defined as the percentage change in the distance covered between the last and first minute of the 6MWT. In addition, relationships between PF and other clinical features were assessed.

RESULTS

Performance fatigability was found in 12/14 pwSMA (85.7%) prior to treatment. The mean distance walked in the sixth minute (71.1 m) was shorter than the distance covered in the first minute (81.8 m), corresponding to a mean PF of 13.1% (95% confidence interval (CI): 6.5-19.6, p = .0007). During treatment with nusinersen, there was a mean reduction in PF of 5.6% (95% CI: -10.0 to -1.3, p = .0148). We found no relationship between PF and fatigue as measured by the Fatigue Severity Scale.

DISCUSSION

This study demonstrates the presence of PF as an independent component of motor impairment and as a potential therapeutic target in our cohort of adult ambulatory pwSMA. Furthermore, the observations in our cohort suggest that nusinersen may have a beneficial effect on PF.

Johnson K, de Hemptinne C, Wong JK. Exploring the layers of fatigue in Parkinson's Disease: A comprehensive analysis of its prevalence and contributing factors

Background

Fatigue is a prevalent yet under-recognized non-motor symptom (NMS) of Parkinson's disease (PD), significantly impacting patients' quality of life. Despite its clinical importance, the relationship between fatigue and other motor and non-motor symptoms remains poorly understood. Its frequent co-occurrence with other NMS further complicates both diagnosis and management, often leading to underdiagnosis and suboptimal treatment. This gap in understanding is largely due to the limited exploration of fatigue in PD.

Objective

This study aimed to evaluate the prevalence of fatigue at baseline and up to 10 years after symptom onset in a large, well-characterized PD cohort (PPMI) and to explore its associations with other non-motor symptoms (NMS). By providing insights into the prevalence and correlations of fatigue, our goal is to highlight the need for early identification and management, guiding future research efforts.

Methods

 We conducted a retrospective study using the PPMI database. Fatigue was assessed using item 1.13 of the Movement Disorders Society Unified Parkinson's Disease Rating Scale. Logistic regression was used to analyze the impact of different variables on fatigue, while point-biserial correlation analysis gauged the relationship between continuous variables and fatigue.

Results

At baseline study visit, 52% (575) of patients reported experiencing fatigue, with 9% reporting moderate to severe fatigue early in the disease course. Higher scores on several scales were significantly associated with an increased risk of fatigue, though most associations were weak. Significant associations included the REM Sleep Behavioral Disorder Questionnaire (OR: 1.09, 95% CI: 1.06-1.11), Geriatric Depression Scale (OR: 1.07, 95% CI: 1.03-1.11), State-Trait Anxiety Inventory (OR: 1.01, 95% CI: 1.00-1.02), SCOPA-Autonomic Dysfunction (OR: 1.05, 95% CI: 1.03-1.06), Epworth Sleepiness Scale (OR: 1.06, 95% CI: 1.04-1.08), and Apathy (OR: 2.90, 95% CI: 2.4-3.5).

Conclusion

Over half of patients reported fatigue at baseline, underscoring its significant prevalence early in PD. The predominantly weak associations with other NMS highlight the necessity for comprehensive patient screening and targeted interventions, as addressing one NMS may not effectively alleviate others.

Fatigue among children and adolescents with acquired brain injury in a specialized neurorehabilitation setting

Introduction

We investigated the fatigue experienced in children and adolescents with acquired brain injury (ABI) undergoing neurorehabilitation.

Methods

Fatigue was assessed using the pediatric quality of life inventory™ (PedsQL™). Multidimensional Fatigue Scale in 38 participants aged 2-19 years with ABI. Data were collected at enrollment and discharge, either from the participants themselves or their parents. The causes of ABI, including stroke, infection, tumor, and traumatic brain injury), were compared.

Results

Participant-reported fatigue levels significantly decreased over time (p = 0.005), whereas parent-reported fatigue levels did not show a significant change. Fatigue levels varied by ABI cause, with stroke-associated fatigue having the least impact and infection-related fatigue showing the greatest impact.

Conclusion

This study highlights the importance of individualized assessments that consider varying etiological factors and advocates for tailored interventions. Further research is needed to fully understand the long-term impacts of fatigue in this population.

Concussion leads to opposing sensorimotor effects of habituation deficit and fatigue in zebrafish larvae

Concussion, or mild traumatic brain injury, is caused by sudden mechanical forces impacting the brain either directly or through inertial loading. This can lead to physical, behavioural and cognitive impairments. Despite concussion being a significant health issue, our understanding of the relationship between initial impact force and the subsequent neurological consequences is not well understood. Previously, we established a model of concussion in zebrafish larvae. Here, we further investigate concussions of varying severities in zebrafish larvae using linear deceleration. Using an acoustic assay to monitor the larval sensorimotor behaviour, we found that different parameters of the resulting escape behaviour are modulated by the impact force of the preceding concussive insult. To investigate the relative contributions of habituation performance and fatigue on the escape response behaviour, we constructed a neurocomputational model. Our findings suggest that a concussive impact initially affects habituation performance at first and, as the impact force increases, fatigue is induced. Fatigue then alters the escape response behaviour in an opposing manner.

Detecting muscle fatigue among community-dwelling senior adults with shape features of the probability density function of sEMG

BACKGROUND

Physical exercise is an important method for both the physical and mental health of the senior population. However, excessive exertion can lead to increased risks of falls, severe injuries, and diminished quality of life. Therefore, simple and effective methods for fatigue monitoring during exercise are highly desirable, particularly in community settings. The purpose of this study was to explore the possibility of real-time detection of exercise-induced fatigue using surface Electromyogram (sEMG) features, including the kurtosis and skewness of the Probability Density Function (PDF) in the community settings to solve the issues of low sensitivity and high computational complexity of commonly used sEMG features.

METHODS

sEMG signals from six forearm muscles were recorded during hand grip tasks at 20% maximal voluntary contraction (MVC) task-to-failure contractions from 30 healthy community-dwelling elders at their respective community centers. PDF shape features of the sEMG, namely kurtosis and skewness, were computed from 25 s of non-fatigue stable phase and 25 s of fatigue data for comparison. Statistical tests were conducted to compare and test for the significance of these features. We further proposed a novel fatigue indicator, Temporal-Mean-Kurtosis (TMK) of channel-averaged kurtosis, to detect fatigue with relatively low computational complexity and adequate sensitivity in community settings. ANOVA and post-hoc analyses were performed to examine the performance of TMK.

RESULTS

Statistically significant differences were found between the non-fatigue period and the fatigue period for both kurtosis and skewness, with increasing values when approaching fatigue. TMK was shown to be sensitive in detecting fatigue with respect to time with lower computational complexity than the Sample Entropy.

CONCLUSION

This study investigated PDF shape features of sEMG signals during a handgrip exercise to identify muscle fatigue in older adults in community experiments. Results revealed significant changes in kurtosis upon fatigue, indicating that PDF shape features were suitable convenient detectors of muscle fatigue in community experiments. The proposed indicator, TMK, showed potential sensitivity in tracking muscle fatigue over time in community-based settings with limited computational complexity, highlighting the promise of sEMG's PDF features in detecting muscle fatigue among the elderly.

Hand fatigability, self-reported fatigue, and functionality in individuals with multiple sclerosis: A cross-sectional study

BACKGROUND

The individual experience of fatigue and fatigability in individuals with Multiple Sclerosis (MS) can vary greatly, beyond the high prevalence of fatigue in MS. Although fatigue is known as a common symptom that affects and potentially limits individuals with MS, it has recently been determined that fatigability also causes consequences that limit individuals' daily lives. The purpose of this study was to compare the associations between self-reported levels of fatigue, measured fatigability, and estimates of functional capacity in people with MS and sex- and age-matched healthy individuals.

METHODS

Twenty-three individuals with Relapsing-Remitting MS (RRMS) diagnosis and 23 age- and sex-matched healthy individuals were included in the study. To examine the fatigability level Dynamic and Static Fatigue Index were used for gross and pinch-grip, and manual dexterity and functionality levels the Scale for the Assessment and Rating of Ataxia (SARA), Nine Hole Peg Test (NHPT), and Dexterity Questionnaire-24 (DextQ-24) were used. While the Fatigue Severity Scale (FSS) and Fatigue Impact Scale (FIS) were used to examine self-reported fatigue, the Beck Depression Inventory (BDI) was used to assess emotional status.

RESULTS

There was no difference between RRMS and healthy individuals in terms of fatigability levels (p > 0.05). While the relationship between Static and Dynamic Fatigue Index gross grip fatigability and FSS and FIS was not found to be statistically significant, the relationship between non-dominant side pinch grip Static Fatigue Index and FSS and FIS was significant. In addition, the relationship between the non-dominant side gross grip Static Fatigue Index and the DextQ-24 dressing and daily activities subsections, and the dominant side pinch grip Dynamic Fatigue Index and the television/compact disk/digital video disk subsection of DextQ-24 was significant (p < 0.05).

CONCLUSION

Fatigability was related to daily life upper limb use for gross grip and self-reported fatigue for pinch grip in individuals with RRMS. It was concluded that future studies focusing on hand fatigability could also consider manual dexterity and self-reported fatigue in individuals with MS from the early-stage. Clarifying the relationship of between fatigability and self-reported fatigue to functioning will allow clinicians to plan more appropriate and directed treatment approaches for individuals with RRMS.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05880745.

Neurophysiological methods for assessing and treating cognitive impairment in multiple sclerosis: A scoping review of the literature

In recent years, there has been a growing interest in exploring the non-classical symptoms of multiple sclerosis (MS), with a particular focus on cognitive impairments associated with the disease's progression. These cognitive symptoms are now recognized as crucial elements in the assessment of disease activity. In this context, neurophysiology has emerged as a valuable and accessible tool for studying and addressing cognitive decline in individuals with MS. This scoping literature review investigates the role of neurophysiology in assessing and treating cognitive impairment in MS patients. The review focuses on Electroencephalography (EEG), Non-Invasive Brain Stimulation (NIBS), and magnetoencephalography (MEG) to assess cognitive decline in MS patients. Moreover, we discuss all the papers that tried to treat this cognitive impairment with NIBS techniques. While several neurophysiological markers show potential, standardization of protocols is essential for enhancing the reliability and consistency of these approaches. Further research is warranted to explore other NIBS techniques and deepen our understanding of the neurophysiological underpinnings of cognitive deficits in MS.

Preference-based utility weights for the Individualized Neuromuscular Quality of Life Questionnaire (INQoL), with a focus on non-dystrophic myotonia (NDM)

INTRODUCTION

The Individualized Neuromuscular Quality of Life Questionnaire (INQoL) is used to measure quality of life in neuromuscular disorders such as non-dystrophic myotonia (NDM). Here we report methods to estimate utilities, with a focus on NDM, from this questionnaire based on two preference elicitation exercises.

METHODS

Eight items from the INQoL were selected with input from three neuromuscular disorder clinical experts with expertise in treating NDM. A discrete choice experiment (DCE) survey of UK general public respondents (n = 508) described outcomes defined by the INQoL items. The same 8 items were also valued using time trade-off (TTO) face-to-face interviews (n = 200). A hybrid regression modelling approach combined both datasets to inform the utility weights.

RESULTS

Hybrid modelling of DCE and TTO data in conjunction improved out-of-sample predictive accuracy. The selected INQoL utility model indicates substantial disutility associated with all eight dimensions of health, with the greatest losses associated with subjective items such as pain and depression.

DISCUSSION

The hybrid modelling approach allows us to combine data from the two methodologies and maximize the information from each to inform the utility weights for the INQoL. The TTO is the more conventional valuation method, but combined with the larger DCE study produced better descriptive coverage. This is a relatively novel method for estimating weights which we think is particularly well suited to economic evaluations of orphan drugs.

[Sociomedical assessment: basics of assessment in general and specifically in the case of fatigue and burnout]

The sociomedical report is an essential basis for making decisions about benefits from social insurance providers. As an instrument of medical information, the sociomedical assessment can be based on very different questions, such as the question of ability to work, earning capacity, participation in professional or social life, or the need for medical treatment. It is important to obtain a comprehensive picture of the individual situation in order to create the basis for decisions about benefit entitlements and support measures. The various issues in the respective sociolegal context may require not only the sociomedical report but also other expertise. The international classification of functioning, disability, and health (ICF) and the World Health Organization (WHO) bio-psycho-social model on which it is based enable health problems and their effects to be considered in the context of life and work. The components of functional ability and disability are assessed in their interaction from a sociomedical perspective. What is important is not the diagnosis but rather the person and the individual impact of the health disorders on their activities and participation.In the case of fatigue and burnout, a medical symptom complex with (psychophysical) exhaustion and the resulting attention and concentration disorders are in the focus of the sociomedical assessment. It can be difficult to objectify symptoms and complaints in these diseases, which can lead to particular challenges during assessment, especially when validating complaints.

Relationship between fatigue and quantitative electromyography findings in patients with myasthenia gravis

Background

Fatigue is a common complaint among patients with myasthenia gravis (MG). In this study, we investigated the alterations in muscle morphology in patients with MG experiencing fatigue using quantitative electromyography (QEMG), and explored the relationship between electrophysiological findings and the severity of both fatigue and disease.

Methods

We performed QEMG of the biceps brachii muscle using the peak ratio method and multi-motor unit potential (MUP) analysis across three groups: 18 MG patients with fatigue, 34 MG patients without fatigue, and 33 healthy subjects. Stimulated single-fiber EMG was performed on the frontalis muscle. The severity of perceived fatigue and disease was subsequently assessed using the quantitative myasthenia gravis (QMG) score, the MG-activities of daily living (MG-ADL) profile, self-reported fatigue questionnaires, and handgrip strength measurements.

Results

The QEMG study revealed a reduced mean MUP duration and size index (SI), in addition to an increased peak ratio in patients with MG (p < 0.05), which tended to be more pronounced in those experiencing fatigue. Compared to healthy subjects, MG patients with fatigue displayed a myopathic pattern characterised by a high peak ratio, short duration, and small-amplitude MUPs, without any increase in the number of phases or small time intervals. The mean peak ratio was positively correlated with the QMG, MG-ADL, and Fatigue Impact Scale total and physical subscores (p < 0.05). Further, MG patients with fatigue exhibited reduced maximum grip strength, which was positively correlated with the mean MUP duration, amplitude, SI, and thickness, and negatively correlated with the mean peak ratio (p < 0.05). No significant differences were observed in the jitter or block measurements (p > 0.05).

Conclusions

The present study investigated electrophysiological findings that were not considered or theorised in prior studies on patients with MG experiencing fatigue. The results of this study suggest that myopathic changes may be a critical pathophysiological component underlying the fatigue associated with MG.

Self-perceptual blindness to mental fatigue in mining workers

Mental fatigue is a psychophysiological state that adversely impacts performance in cognitive tasks, increasing risk of occupational hazards. Given its manifestation as a conscious sensation, it is often measured through subjective self-report. However, subjective measures are not always true measurements of objective fatigue. In this study, we investigated the relationship between objective and subjective fatigue measurements with the preventive AccessPoint fatigue assay in Chilean mine workers. Subjective fatigue was measured through the Samn-Perelli scale, objective fatigue through a neurocognitive reaction time task. We found that objective and subjective fatigue do not correlate (-0.03 correlation coefficient, p < 0.001). Moreover, severe fatigue cases often displayed absence of subjective fatigue coupled with worse cognitive performance, a phenomenon we denominated Perceptual Blindness to fatigue. These findings highlight the need for objective fatigue measurements, particularly in high-risk occupational settings such as mining. Our results open new avenues for researching mechanisms underlying fatigue perception and its implications for occupational health and safety.

Comparative study for fatigue prevalence in subjects with diseases: a systematic review and meta-analysis

Fatigue is one of the common symptoms in individuals with diseases or disorders, significantly affecting quality of life (QoL) and the prognosis of diseases. This study aimed to comprehensively compare the features of fatigue across a wide range of diseases. We systematically searched the PubMed and Cochrane Library databases from inception to March 31st, 2021, and conducted a meta-analysis to generate precise estimates. The analyses were stratified by classification of diseases, gender, and severity of fatigue (moderate and severe), and study quality was assessed using the Newcastle-Ottawa Scale (NOS). In total, 214 articles (233 prevalence data) met our eligibility criteria, covering 102,024 participants (mean 438 ± 1,421) across 88 diseases. Among these, seventy-eight data sets (52,082 participants) and thirty-nine data sets (10,389 participants) reported gender- and severity-related fatigue prevalence. The overall prevalence among subjects with 88 diseases was 49.4% [95% CI 46.9-52.1]. According to the International Classification of Diseases-10 (ICD-10) classification, the highest prevalence of fatigue (65.9% [95% CI 54.9-79.6]) was observed in patients with mental/behavioral diseases, whereas the lowest prevalence (34.7% [95% CI 24.5-49.2]) was found among those with circulatory system diseases. A slight female dominance (43.5% vs. 49.8%) was observed in the total data, with the most notable female predominance (1.8-fold) seen in patients with low back pain. The top disease groups with a moderate to severe level of fatigue included gastroparesis (92.3%), pulmonary hypertension (90.0%), chronic obstructive pulmonary disease (COPD, 83.2%), and multiple sclerosis (80.0%). These results are the first to comprehensively show the comparative features of fatigue prevalence among subjects across 88 diseases. Our findings provide valuable reference data for future research on fatigue and for the management of patients with fatigue.Prospero registration number: CRD42021270494.

Perceived physical and mental fatigability in older adults with and without multiple sclerosis

BACKGROUND

Fatigue stands out as a prevalent and debilitating symptom in both Multiple Sclerosis (MS) and the aging population. Traditional methods for measuring perceived fatigue may not adequately account for individual activity differences, leading to varied prevalence rates. Perceived fatigability anchors fatigue to specific activities with predetermined intensity and duration, thereby mitigating self-pacing bias. Despite its potential, perceived fatigability is poorly understood in older adults, particularly those with neurological conditions, including MS. This study thus aimed to (1) investigate whether, among older adults, MS was associated with worse perceived physical and mental fatigability; (2) evaluate whether, among older adults with MS (OAMS), greater patient-reported disease-related disability was associated with worse perceived physical and mental fatigability.

METHODS

Participants were 96 older adults with a physician-confirmed diagnosis of MS (mean age: 64.6 ± 4.2) and 110 healthy controls (mean age: 68.2 ± 7.2), all confirmed to be dementia-free through established case conference procedures. Physical and mental fatigability were measured using the Pittsburgh Fatigability Scale, a 10-item questionnaire (score range: 0 to 50) designed to assess fatigue levels that individuals expect to feel after engaging in a range of typical activities for older adults. MS disease-related disability was assessed with the Patient Determined Disease Steps scale, which ranges from 0 (normal) to 8 (bedridden), with scores ≥ 2 indicating worse MS-related disability after a median split. Separate linear regression models were performed to investigate associations between group status (MS vs. Control) as the predictor and perceived physical and mental fatigability scores as the outcome variables. Within the MS group, additional linear regression models were performed to explore the relationship between disease-related disability and fatigability levels. All models adjusted for age, sex, race, education, global health, general cognitive function, and depressive symptoms levels.

RESULTS

The fully adjusted models yielded the following key findings: OAMS reported significantly higher levels of perceived physical fatigability (M = 25.11 ± 9.67) compared to controls (M = 17.95 ± 8.35) (p = 0.003). Similarly, the perceived mental fatigability in OAMS (M = 16.82 ± 11.79) was significantly greater than that in controls (M = 9.15 ± 7.12) (p = 0.003). Within the MS group, individuals with greater disease-related disability reported significantly greater levels of both physical (M = 30.13 ± 7.71 vs. 18.67 ± 8.00, p < 0.001) and mental fatigability (M = 20.31 ± 12.18 vs. 12.33 ± 9.69, p = 0.009) compared to those with lower MS-related disability. Of note, the significance of these findings persisted in models that adjusted for depressive symptoms.

CONCLUSION

Our study provides compelling evidence that OAMS exhibit significantly higher perceived physical and mental fatigability compared to healthy controls. Additionally, worse MS-related disability correlates with worse physical and mental fatigability. These results persist after adjusting for confounders including depressive symptoms. Our findings underscore the necessity of holistic management strategies that cater to both physical and psychological aspects of MS, laying a foundation for future studies to uncover the pathophysiological mechanisms of fatigability in older adults with and without MS.

Submaximal force-velocity relationships during mountain ultramarathon: Data from the field

This study presents a novel method for evaluating the submaximal velocity-force (V(F)) relationship in mountain ultramarathon races using crowdsourced data from Strava.com. The dataset includes positional data from 408 participants of the 171-km UTMB® 2023 race (9,850-m D+). The race was divided into 100-m segments. The mean net propulsive force and velocity were computed for each segment to describe the submaximal V(F) relationship as a rational function of three parameters. F1: propulsive force at 1 m · s-1; V0: theoretical maximum velocity on flat terrain; C: curvature parameter (the lower C, the more linear the V(F) relationship). The V(F) profile parameters were found to be F1 = 1.80 ± 0.33 N · kg-1, V0 = 2.36 ± 0.42 m · s-1, and C = 0.66 ± 1.81, with good independence between the parameters within a group of homogeneous performance. The best athletes had the highest F1, V0, and C values. V(F) parameters were affected by fatigue during the race, with decreases of 20.9%, 32.0%, and 59.8% between the first and second parts of the race respectively. These findings suggest that the V(F) relationship is an interesting original approach for studying performance and fatigability during mountain ultra-endurance races.

Somatosensory processing in long COVID fatigue and its relations with physiological and psychological factors

Fatigue is prevalent amongst people with long COVID, but is poorly understood. The sensory attenuation framework proposes that impairments in sensory processing lead to heightened perception of effort, driving fatigue. This study aims to investigate the role of somatosensory processing impairments in long COVID fatigue and quantify how sensory processing relates to other prominent symptoms of long COVID including autonomic dysfunction, mood and illness beliefs in driving the experience of fatigue. We will recruit 44 individuals with long COVID fatigue and 44 individuals with neither long COVID nor fatigue (controls). Our primary objective is to compare baseline somatosensory processing between individuals with long COVID fatigue and controls. Additionally, we will explore the associations between somatosensory processing, fatigability and the level of fatigue induced by cognitive and physical exertion. Due to the complex nature of fatigue, we will also investigate how long COVID, state fatigue, perceived effort, mood, illness beliefs, autonomic symptoms and autonomic nervous system function interact to predict trait fatigue. This comprehensive investigation aims to elucidate how sensory processing and other prominent symptoms interact to impact the experience of fatigue.

Six-minute walk test as outcome measure of fatigability in adults with spinal muscular atrophy treated with nusinersen

INTRODUCTION/AIMS

Fatigue (subjective perception) and fatigability (objective motor performance worsening) are relevant aspects of disability in individuals with spinal muscular atrophy (SMA). The effect of nusinersen on fatigability in SMA patients has been investigated with conflicting results. We aimed to evaluate this in adult with SMA3.

METHODS

We conducted a multicenter retrospective cohort study, including adult ambulant patients with SMA3, data available on 6-minute walk test (6MWT) and Hammersmith Functional Motor Scale-Expanded (HFMSE) at baseline and at least at 6 months of treatment with nusinersen. We investigated fatigability, estimated as 10% or higher decrease in walked distance between the first and sixth minute of the 6MWT, at baseline and over the 14-month follow-up.

RESULTS

Forty-eight patients (56% females) were included. The 6MWT improved after 6, 10, and 14 months of treatment (p < 0.05). Of the 27 patients who completed the entire follow-up, 37% improved (6MWT distance increase ≥30 m), 48.2% remained stable, and 14.8% worsened (6MWT distance decline ≥30 m). Fatigability was found at baseline in 26/38 (68%) patients and confirmed at subsequent time points (p < 0.05) without any significant change over the treatment period. There was no correlation between fatigability and SMN2 copy number, sex, age at disease onset, age at baseline, nor with 6MWT total distance and baseline HFMSE score.

DISCUSSION

Fatigability was detected at baseline in approximately 2/3 of SMA3 walker patients, without any correlation with clinical features, included motor performance. No effect on fatigability was observed during the 14-month treatment period with nusinersen.

Enhanced Muscle Endurance Through Self-regulated Dual-Task Exercises in Elbow Fracture Rehabilitation: A Cross-sectional Study

OBJECTIVE

The main objective of this study was to investigate the effect of a self-regulated dual task on muscle endurance within a single rehabilitation session in patients recovering from an elbow fracture.

DESIGN

This is a cross-sectional study of individuals recovering from elbow fractures ( N = 20). Muscle endurance was tested using elastic bands at Borg's CR10 intensity 3-during four conditions: single-task and dual-task for elbow flexion and extension.

RESULTS

The cognitive condition significantly influenced muscle endurance ( P < 0.001), while the type of elbow exercise (flexion or extension) did not show significant differences ( P = 0.592). The perceived difficulty of the tasks showed a significant interaction effect ( P = 0.032). The dual-task condition showed an average increase of about 15 repetitions. A moderate negative correlation was found between the differences in repetitions and the perceived difficulty of the flexion exercise ( r = 0.677, P = 0.001).

CONCLUSIONS

Dual-task with self-regulation enhances muscle endurance among patients recovering from an elbow fracture. However, the improvements seem to depend on the perceived difficulty of the cognitive task. Future randomized controlled trials are required to understand the therapeutic implications of dual-tasking.

Activation of skeletal muscle mechanoreceptors and nociceptors reduces the exercise performance of the contralateral homologous muscles

Increasing evidence suggests that activation of muscle nerve afferents may inhibit central motor drive, affecting contractile performance of remote exercising muscles. Although these effects are well documented for metaboreceptors, very little is known about the activation of mechano- and mechanonociceptive afferents on performance fatigability. Therefore, the purpose of the present study was to examine the influence of mechanoreceptors and nociceptors on performance fatigability. Eight healthy young males undertook four randomized experimental sessions on separate occasions in which the experimental knee extensors were the following: 1) resting (CTRL), 2) passively stretched (ST), 3) resting with delayed onset muscle soreness (DOMS), or 4) passively stretched with DOMS (DOMS+ST), whereas the contralateral leg performed an isometric time to task failure (TTF). Changes in maximal voluntary contraction (ΔMVC), potentiated twitch force (ΔQtw,pot), and voluntary muscle activation (ΔVA) were also assessed. TTF was reduced in DOMS+ST (-43%) and ST (-29%) compared with CTRL. DOMS+ST also showed a greater reduction of VA (-25% vs. -8%, respectively) and MVC compared with CTRL (-28% vs. -45%, respectively). Rate of perceived exertion (RPE) was significantly increased at the initial stages (20-40-60%) of the TTF in DOMS+ST compared with all conditions. These findings indicate that activation of mechanosensitive and mechanonociceptive afferents of a muscle with DOMS reduces TTF of the contralateral homologous exercising limb, in part, by reducing VA, thereby accelerating mechanisms of central fatigue.NEW & NOTEWORTHY We found that activation of mechanosensitive and nociceptive nerve afferents of a rested muscle group experiencing delayed onset muscle soreness was associated with reduced exercise performance of the homologous exercising muscles of the contralateral limb. This occurred with lower muscle voluntary activation of the exercising muscle at the point of task failure.

The therapeutic potential of exercise for improving mobility in multiple sclerosis

Multiple sclerosis (MS) is a chronic autoimmune disease characterized by inflammation and demyelination in the central nervous system (CNS) with subsequent axonal and neuronal degeneration. These changes are associated with a broad range of symptoms including skeletal muscle dysfunction. Importantly, musculoskeletal impairments manifest in various ways, compromise the quality of life and often precede the later development of mobility disability. As current standard disease modifying therapies for MS predominantly act on neuroinflammation, practitioners and patients face an unmet medical need for adjunct therapies specifically targeting skeletal muscle function. This review is intended to detail the nature of the skeletal muscle dysfunctions common in people with MS (pwMS), describe underlying intramuscular alterations and outline evidence-based therapeutic approaches. Particularly, we discuss the emerging role of aerobic and resistance exercise for reducing the perception of fatigue and increasing muscle strength in pwMS. By integrating the most recent literature, we conclude that both exercise interventions should ideally be implemented as early as possible as they can address MS-specific muscle impairments. Aerobic exercise is particularly beneficial for pwMS suffering from fatigue and metabolic impairments, while resistance training efficiently counters muscle weakness and improves the perception of fatigue. Thus, these lifestyle interventions or possible pharmacological mimetics have the potential for improving the general well-being and delaying the functional declines that are relevant to mobility.

Understanding the mechanisms of fatigue in multiple sclerosis: linking interoception, metacognition and white matter dysconnectivity

One of the most prominent symptoms in multiple sclerosis is pathological fatigue, often described by sufferers as one of the most debilitating symptoms, affecting quality of life and employment. However, the mechanisms of both, physical and cognitive fatigue in multiple sclerosis remain elusive. Here, we use behavioural tasks and quantitative MRI to investigate the neural correlates of interoception (the ability to sense internal bodily signals) and metacognition (the ability of the brain to assess its own performance), in modulating cognitive fatigue. Assuming that structural damage caused by multiple sclerosis pathology might impair the neural pathways subtending interoception and/or metacognition, we considered three alternative hypotheses to explain fatigue as a consequence of, respectively: (i) reduced interoceptive accuracy, (ii) reduced interoceptive insight or (iii) reduced global metacognition. We then explored associations between these behavioural measures and white matter microstructure, assessed by diffusion and magnetisation transfer MRI. Seventy-one relapsing-remitting multiple sclerosis patients participated in this cross-sectional study (mean age 43, 62% female). Patient outcomes relevant for fatigue were measured, including disability, disease duration, depression, anxiety, sleepiness, cognitive function, disease modifying treatment and quality of life. Interoceptive and metacognitive parameters were measured using heartbeat tracking and discrimination tasks, and metacognitive visual and memory tasks. MRI was performed in 69 participants, including diffusion tensor MRI, neurite orientation dispersion and density imaging and quantitative magnetisation transfer. Associations between interoception and metacognition and the odds of high cognitive fatigue were tested by unconditional binomial logistic regression. The odds of cognitive fatigue were higher in the people with low interoceptive insight (P = 0.03), while no significant relationships were found between fatigue and other interoceptive or metacognitive parameters, suggesting a specific impairment in interoceptive metacognition, rather than interoception generally, or metacognition generally. Diffusion MRI-derived fractional anisotropy and neurite density index showed significant (P < 0.05) negative associations with cognitive fatigue in a widespread bilateral white matter network. Moreover, there was a significant (P < 0.05) interaction between cognitive fatigue and interoceptive insight, suggesting that the poorer the white matter structure, the lower the interoceptive insight, and the worse the fatigue. The results point towards metacognitive impairment confined to the interoceptive domain, in relapsing-remitting patients with cognitive fatigue. The neural basis of this impairment is supported by a widespread white matter network in which loss of neurite density plays a role.

Vocal Fold Vibratory Dose and Perceived Exertion Responses to the Fluid Interval Test for Voice (FIT-V): A Novel Vocal Loading Task Platform

INTRODUCTION

Vocal loading tasks are often used to study how specific variables influence downstream vocal effort or fatigue. The current study introduces a novel vocal loading task, the Fluid Interval Test for Voice (FIT-V) that combines laryngeal diadochokinesis, intervallic rest and exercise, and fluid back pressure. To assess the differences between this novel task and existing vocal loading tasks, we measured vocal fold vibratory dose and perceived phonatory exertion across three 30-minute task conditions: a control loud oral reading task (LOR), a back pressure-resisted Fluid Interval Test for Voice (FIT-V5), and an unresisted Fluid Interval Test for Voice (FIT-V0).

METHODS

Following a training session, 30 participants completed the three tasks (LOR, FIT-V0, and FIT-V5) in counterbalanced order on different days. Vocal fold cycle (Aim 1A) and distance doses (Aim 1B) were collected continuously using a dosimeter. The overall perceived phonatory exertion (Aim 2A) was rated once per minute, while anatomically localized cognitive, laryngeal, thoracic, abdominal, and articulatory exertion (Aim 2B) were rated once at the end of each task. Statistical analyses examined the effects of task and task× time interactions on the dependent variables.

RESULTS

The FIT-V0 and FIT-V5 tasks imposed smaller vocal fold cycle doses (P < 0.001; Aim 1A) and distance doses (P < 0.001; Aim 1B) than the LOR task while eliciting comparable or greater magnitudes of overall perceived phonatory exertion (P = 0.003; Aim 2A). However, anatomically localized perceived exertion was greater in the abdomen and thorax (P < 0.05) and lesser in the anterior neck (P < 0.05) in the two FIT-V tasks relative to the LOR task (Aim 2B). Absolute forced vital capacity was a significant predictor of most forms of anatomically localized perceived exertion.

DISCUSSION

The unresisted FIT-V0 and the back pressure-resisted FIT-V5 tasks yielded similar profiles of overall perceived phonatory exertion, despite vocal fold vibratory doses roughly half that of the LOR task. However, the anatomically localized perceived exertion data underscored subtle across-task differences not apparent in the overall ratings, suggesting potentially distinct physiological and perceptual niches for the three task protocols.

Frontal-striatal glucose metabolism and fatigue in patients with multiple sclerosis, long COVID, and COVID-19 recovered controls

This study compared brain glucose metabolism using FDG-PET in the caudate nucleus, putamen, globus pallidus, thalamus, and dorsolateral prefrontal cortex (DLPFC) among patients with Long COVID, patients with fatigue, people with multiple sclerosis (PwMS) patients with fatigue, and COVID recovered controls. PwMS exhibited greater hypometabolism compared to long COVID patients with fatigue and the COVID recovered control group in all studied brain areas except the globus pallidus (effect size range 0.7-1.5). The results showed no significant differences in glucose metabolism between patients with Long COVID and the COVID recovered control group in these regions. These findings suggest that long COVID fatigue may involve non-CNS systems, neurotransmitter imbalances, or psychological factors not captured by FDG-PET, while MS-related fatigue is associated with more severe frontal-striatal circuit dysfunction due to demyelination and neurodegeneration. Symmetrical standardized uptake values (SUVs) between hemispheres in all groups imply that fatigue in these conditions may be related to global or network-level alterations rather than hemisphere-specific changes. Future studies should employ fine-grained analysis methods, explore other brain regions, and control for confounding factors to better understand the pathophysiology of fatigue in MS and long COVID. Longitudinal studies tracking brain glucose metabolism in patients with Long COVID could provide insights into the evolution of metabolic patterns as the condition progresses.

Perceived Factors That Contributed to Task Termination during Fatiguing Tasks Anchored to Perceptual Intensities

This study examined the effects of sustained, isometric forearm flexion tasks anchored to ratings of perceived exertion of 2 (RPE2FT) and 8 (RPE8FT) on the patterns of fatigue-induced changes in torque and neuromuscular responses, time to task failure (TTF), performance fatigability (% decline in maximal voluntary isometric contraction [MVIC]), and perceived factors that contributed to task termination. Twelve men (mean ± SD: age = 20.9 ± 2.2 yrs) performed MVICs before and after the tasks and completed post-test questionnaires (PTQ). Data were analyzed using polynomial regression analyses, dependent t-tests, Spearman's rank order correlations, and Wilcoxon signed rank tests. The RPE8FT had greater (p < 0.001) performance fatigability than the RPE2FT, despite no difference (p > 0.05) in TTF. During both tasks, there were significant (p ≤ 0.05) composite linear decreases for torque, electromyographic amplitude, and neuromuscular efficiency, and substantial individual variability in the neuromuscular responses. There were no significant (p > 0.05) associations among the perceived factors and TTF or performance fatigability. Thus, there were RPE-specific differences in performance fatigability, but not TTF or the composite patterns of changes in torque and neuromuscular responses. In addition, in most cases, the individual neuromuscular, but not torque, patterns of responses were RPE-specific. Furthermore, the perceived factors assessed by the PTQ were not related to TTF or performance fatigability.

Investigation of Neuromuscular Activation in Older Female Adults during a Dynamic and Challenging Virtual Reality Activity: A Cross-Sectional Study

The use of virtual reality (VR) in older adults promotes improvements in mobility, strength, and balance. Changes in neuromuscular activation have been found to be associated with these improvements; however, during VR activities, this aspect has not been thoroughly investigated. The aim of this study was to investigate neuromuscular activation among older female adults during VR activities. Sixteen older female adults, with the use of VR, performed dynamic punching movements involving elbow flexion/extension for one minute, and the muscle activation of the bicep brachii was recorded with electromyography (EMG) and normalized to the maximal voluntary isometric contraction of elbow flexion. The one-minute activity was divided into three time phases: 0-10 s, 25-35 s, and 50-60 s. The five highest EMG amplitude values (%) in each phase were selected and averaged. Differences between phases were analyzed using repeated ANOVA (αadj = 0.017). The EMG amplitude for the first phase was 39.1 ± 2.6%, that for the second phase was 44.8 ± 3.0%, and that for the third phase was 49.6 ± 3.1%. Statistically significant differences were found in all phases, with the first phase demonstrating a lower EMG amplitude (%) compared to the second (p = 0.002) and third phases (p = 0.000). The third phase demonstrated a higher EMG amplitude (%) compared to the second phase (p = 0.025). Engagement in VR activities can have significant effects on neuromuscular activation in older female adults, with our findings revealing a significant increase in the EMG amplitude within one minute of commencing a dynamic and challenging activity such as virtual boxing.

Fatigue in early multiple sclerosis: MRI metrics of neuroinflammation, relapse and neurodegeneration

Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease affecting the brain and spinal cord. Fatigue is a common disabling symptom from MS onset, however the mechanisms by which underlying disease processes cause fatigue remain unclear. Improved pathophysiological understanding offers potential for improved treatments for MS-related fatigue. MRI provides insights into in vivo neuroinflammatory activity and neurodegeneration, although existing evidence for imaging correlates of MS fatigue is mixed. We explore associations between fatigue and MRI measures in the brain and spinal cord to identify neuroinflammatory and regional neurodegenerative substrates of fatigue in early relapsing-remitting MS (RRMS). Recently diagnosed (<6 months), treatment-naive people with RRMS (n = 440) were recruited to a longitudinal multi-centre nationally representative cohort study. Participants underwent 3-Tesla brain MRI at baseline and one year. We calculated global and regional white and grey matter volumes, white matter lesion (WML) load and upper cervical spinal cord cross-sectional area levels C2-3, and assessed new/enlarging WMLs visually. Participants were classed as fatigued or non-fatigued at baseline according to the Fatigue Severity Scale (>/≤36). Disability and depression were assessed with the expanded-disability status scale and Patient Health Questionnaire, respectively. MRI measures were compared between fatigue groups, both cross-sectionally and longitudinally, using regression analyses. Higher disability and depression scores were observed for participants with fatigue, with a higher number of fatigued participants receiving disease-modifying treatments at follow-up. Structural MRI data for brain were available for n = 313 (45% fatigued) and for spinal cord for n = 324 (46% fatigued). Cervical spinal cord cross-sectional area 2-3, white and grey matter volumes decreased, and WML volume increased, over time for both groups (q < 0.05). However, no significant between-group differences in these measures were found either cross-sectionally or longitudinally (q > 0.05). The presence of new/enlarging WMLs (49% in fatigued; 51% in non-fatigued) at follow-up also did not differ between groups (q > 0.05). Our results suggest that fatigue is not driven by neuroinflammation or neurodegeneration measurable by current structural MRI in early RRMS. This novel negative finding in a large multi-centre cohort of people with recently diagnosed RRMS helps to resolve uncertainty in existing literature. Notably, we showed that fatigue is prevalent in patients without brain radiological relapse, who may be considered to have inactive disease. This suggests that symptom detection and treatment should remain a clinical priority regardless of neuroinflammatory disease activity. More sensitive objective biomarkers are needed to elucidate fatigue mechanisms in RRMS, and ultimately facilitate development of effective targeted treatments for this important 'hidden disability'.

Comparison of Force, Neuromuscular, and Metabolic Responses During Sustained, Isometric Handgrip Holds to Failure Anchored to Low and High Perceptual Intensities in Men: An Exploratory Study

ABSTRACT

Kwak, M, Succi, PJ, Benitez, B, Mitchinson, C, Samaan, MA, Abel, MG, and Bergstrom, HC. Comparison of force, neuromuscular, and metabolic responses during sustained, isometric handgrip holds to failure anchored to low and high perceptual intensities in men: An exploratory study. J Strength Cond Res 38(8): e405-e416, 2024-This study examined the responses of force alterations, relative to critical force (CF), neuromuscular parameters, and muscle oxygenation (SmO2) for isometric handgrip holds to failure (HTF) anchored to ratings of perceived exertion (RPE) of 3 and 7. Twelve men completed pre-maximal voluntary isometric contractions (pre-MVIC), submaximal HTF at 4 percentages of pre-MVIC, HTF at RPE = 3 and 7, and post-MVIC. Mechanomyograpic (MMG) signals and SmO2 were recorded during the RPE HTF. Analyses included paired-samples t-tests and repeated-measures ANOVAs at an alpha level of p ≤ 0.05. Time to task failure was not different between RPE 3 (478.7 ± 196.6 s) and RPE 7 (495.8 ± 173.8 s). Performance fatigability (PF) and MMG amplitude (AMP) were greater for RPE 7 (PF: 37.9 ± 12.9%; MMG AMP: 15.7 ± 7.4% MVIC) than RPE 3 (PF: 30.0 ± 14.5%; MMG AMP: 10.2 ± 6.5% MVIC), but MMG mean power frequency (MPF) was greater for RPE 3 (146.2 ± 31.1% MVIC) than RPE 7 (128.8 ± 23.0% MVIC). There were RPE-dependent decreases in force (p ≤ 0.01) across 3 discernable phases during the HTF. There were decreases in MMG AMP across time for both RPEs, but there were no significant changes in MMG MPF or SmO2. There were overall similar motor unit control strategies and local metabolic demand between RPEs. The majority of the HTF performed below CF at RPE 3 and 7 indicated CF did not reflect the highest sustainable force. When prescribing isometric exercise anchored to RPE, practitioners should be aware of the magnitude of force loss and relative intensity of the task to be sure desired training loads are met.

Complementary and Integrative Medicine in Treating Headaches, Cognitive Dysfunction, Mental Fatigue, Insomnia, and Mood Disorders Following Traumatic Brain Injury: A Comprehensive Review

Traumatic brain injury (TBI) is a complex condition associated with a range of persistent symptoms including headaches, cognitive dysfunction, mental fatigue, insomnia, and mood disorders. Conventional treatments for TBI-related symptoms can be insufficient, leading to interest in complementary and integrative medicine (CIM) approaches. This comprehensive article examines the existing literature on CIM modalities, including mind-body interventions, acupuncture/acupressure, herbal remedies, nutritional supplements, biofeedback, yoga, and tai chi in the context of managing secondary complications following TBI. The article highlights potential benefits and limitations of CIM modalities, while acknowledging the need for further research to better establish efficacy and safety in this specific population.

Effects of acute simulated altitude on the maximal lactate steady state in humans

We sought to determine the effects of acute simulated altitude on the maximal lactate steady state (MLSS) and physiological responses to cycling at and 10 W above the MLSS-associated power output (PO) (MLSSp and MLSSp+10, respectively). Eleven (4 females) participants (means [SD]; 28 [4] yr; V̇o2max: 54.3 [6.9] mL·kg-1·min-1) acclimatized to ∼1,100 m performed 30-min constant PO trials in simulated altitudes of 0 m sea level (SL), 1,111 m mild altitude (MILD), and 2,222 m moderate altitude (MOD). MLSSp, defined as the highest PO with stable (<1 mM change) blood lactate concentration ([BLa]) between 10 and 30 min, was significantly lower in MOD (209 [54] W) compared with SL (230 [56] W; P < 0.001) and MILD (225 [58] W; P = 0.001), but MILD and SL were not different (P = 0.12). V̇o2 and V̇co2 decreased at higher simulated altitudes due to lower POs (P < 0.05), but other end-exercise physiological responses (e.g., [BLa], ventilation [V̇e], heart rate [HR]) were not different between conditions at MLSSp or MLSSp + 10 (P > 0.05). At the same absolute intensity (MLSSp for MILD), [BLa], HR, and V̇E and all perceptual variables were exacerbated in MOD compared with SL and MILD (P < 0.05). Maximum voluntary contraction, voluntary activation, and potentiated twitch forces were exacerbated at MLSSp + 10 relative to MLSSp within conditions (P < 0.05); however, condition did not affect performance fatiguability at the same relative or absolute intensity (P > 0.05). As MLSSp decreased in hypoxia, adjustments in PO are needed to ensure the same relative intensity across altitudes, but common indices of exercise intensity may facilitate exercise prescription and monitoring in hypoxia.NEW & NOTEWORTHY This study demonstrates the power output and metabolic rate associated with the maximal lactate steady-state (MLSS) decline in response to simulated altitude; however, common indices of exercise intensity remained unchanged when cycling was performed at the work rate associated with MLSS at each simulated altitude. These results support previous studies that investigated the effects of hypoxia on alternative measures of the critical intensity of exercise and will inform exercise prescription/monitoring across altitudes.

Metaplastic neuromodulation via transcranial direct current stimulation has no effect on corticospinal excitability and neuromuscular fatigue

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation tool with potential for managing neuromuscular fatigue, possibly due to alterations in corticospinal excitability. However, inconsistencies in intra- and inter- individual variability responsiveness to tDCS limit its clinical use. Emerging evidence suggests harnessing homeostatic metaplasticity induced via tDCS may reduce variability and boost its outcomes, yet little is known regarding its influence on neuromuscular fatigue in healthy adults. We explored whether cathodal tDCS (ctDCS) prior to exercise combined with anodal tDCS (atDCS) could augment corticospinal excitability and attenuate neuromuscular fatigue. 15 young healthy adults (6 males, 22 ± 4 years) participated in four pseudo-randomised neuromodulation sessions: sham stimulation prior and during exercise, sham stimulation prior and atDCS during exercise, ctDCS prior and atDCS during exercise, ctDCS prior and sham stimulation during exercise. The exercise constituted an intermittent maximal voluntary contraction (MVC) of the right first dorsal interosseous (FDI) for 10 min. Neuromuscular fatigue was quantified as an attenuation in MVC force, while motor evoked potential (MEP) amplitude provided an assessment of corticospinal excitability. MEP amplitude increased during the fatiguing exercise, whilst across time, force decreased. There were no differences in MEP amplitudes or force between neuromodulation sessions. These outcomes highlight the ambiguity of harnessing metaplasticity to ameliorate neuromuscular fatigue in young healthy individuals.

An online self-study mindfulness-based stress reduction course for people suffering from mental fatigue after an acquired brain injury

OBJECTIVE

The Mindfulness-Based Stress Reduction (MBSR) program has shown promising results for people suffering from mental fatigue after an acquired brain injury. The aim was to evaluate the feasibility of a MBSR program performed as an online self-study course for this group of people.

METHODS

Sixty participants who had suffered an acquired brain injury with lasting mental fatigue were randomized to an online MBSR course or to a waitlist control group. They answered self-report questionnaires before start and after the course.

RESULTS

Sixteen completed the MBSR program. With the repeated ANOVA no significant difference between groups was found, although there was a significant change in time (the repetition factor). The post-hoc paired t-test indicated a significant reduction and a large-to-median effect size in mental fatigue (p = 0.003, d = 0.896), depression (p = 0.038, d = 0.569) and anxiety (p = 0.030, d = 0.598) for the MBSR group. No significant changes were found for the control group.

CONCLUSION

An online self-study MBSR program for people suffering from mental fatigue after an acquired brain injury can be a feasible option for those suffering from less severe mental fatigue and emotional symptoms, while others may require a program adapted to their needs.

Insight into motor fatigue mechanisms in natalizumab treated multiple sclerosis patients with wearing off

Motor fatigue in Multiple Sclerosis (MS) is due to reduced motor cortex (M1) output and altered sensorimotor network (SMN) modulation. Natalizumab, a disease-modifying therapy, reduces neuroinflammation and improves fatigue. However, some patients treated with natalizumab experience fatigue recurrence ('wearing-off') before subsequent infusions. Wearing-off provides a valuable window into MS-related motor fatigue mechanisms in a controlled, clinically stable, setting. This study investigates whether wearing-off is associated with worsening motor fatigue and its neurophysiological mechanisms and assesses natalizumab's effect on MS-related fatigue. Forty-five relapsing-remitting MS patients with wearing-off symptoms were evaluated pre- and post-natalizumab infusion. Assessments included evaluating disability levels, depressive symptoms, and the impact of fatigue symptoms on cognitive, physical, and psychosocial functioning. The motor fatigue index was computed through the number of blocks completed during a fatiguing task and peripheral, central, and supraspinal fatigue (M1 output) were evaluated by measuring the superimposed twitches evoked by peripheral nerve and transcranial magnetic stimulation of M1. Transcranial magnetic stimulation-electroencephalography assessed M1 effective connectivity by measuring TMS-evoked potentials (TEPs) within the SMN before- and after the task. We found that wearing-off was associated with increased motor fatigue index, increased central and supraspinal fatigue, and diminished task-related modulation of TEPs compared to post-natalizumab infusion. Wearing-off was also associated with worsened fatigue impact and depression symptom scores. We conclude that the wearing-off phenomenon is associated with worsening motor fatigue due to altered M1 output and modulation of the SMN. Motor fatigue in MS may reflect reversible, inflammation-related changes in the SMN that natalizumab can modulate. Our findings apply primarily to MS patients receiving natalizumab, emphasizing the need for further research on other treatments with wearing-off.

The Influence of Changes in Daily Life Habits and Well-Being on Fatigue Level During COVID-19 Pandemic

The COVID-19 pandemic and its lockdown in March 2020 have led to changes in lifestyle and increased levels of anxiety, depression, and fatigue. This survey examined a number of factors (anxiety state, sleep quality, daily activities, mental load, work-related variables) influencing mental and physical fatigue during lockdown and how these relations have evolved one year later. A cohort of 430 workers and 124 retirees were recruited in April-May 2020 (lockdown period, data set 1), and a subsample (133 workers and 40 retirees) completed the same questionnaire in April-May 2021 (data set 2). Linear regression models showed a significant subjective increase in both physical and mental fatigue in both worker and retiree groups during lockdown, and a supplementary increase in physical fatigue and anxiety level in spring 2021 compared to the lockdown period. During lockdown, anxiety level, concerns about COVID-19, work flexibility, mental load, and sleep metrics were associated with the evolution of fatigue among workers. For retirees, only anxiety and physical activity levels were linked to changes in physical fatigue. In April-May 2021, the only associations which remained significant were those in workers between fatigue and anxiety level and workload. These findings suggest that the increased fatigue levels during the lockdown are likely due to the swift and significant changes in daily routines (such as sleep patterns and work dynamics) and psychological states (including increased anxiety and concerns) prompted by the sanitary crisis. On the other hand, the increase in fatigue observed one year after the beginning of the pandemic seems to result from more psychological factors associated with the health situation.

Probing sustained attention and fatigue across the lifespan

Trait fatigues reflects tiredness that persists throughout a prolonged period, whereas state fatigue is a short-term reaction to intense or prolonged effort. We investigated the impact of sustained attention (using the SART) on both trait and state fatigue levels in the general population. An online version of the SART was undertaken by 115 participants, stratified across the whole adult lifespan. While pre-task trait fatigue was a strong indicator of the initial state fatigue levels, undergoing the task itself induced an increase in reported subjective state fatigue, and an accompanying reduction in subjective energy rating. Consistent with this finding, greater subjective state fatigue levels were associated with reduced accuracy. In addition, age was the best predictor of inter-participant accuracy (the older the participants, the greater the accuracy), and learning (i.e., task duration reducing reaction times). Moreover, a ceiling effect occurred where participants with higher trait fatigue did not experience greater state fatigue changes relative to those with low trait scores. In summary, we found improved accuracy in older adults, as well as a tight coupling between state fatigue and SART performance decline (in an online environment). The findings warrant further investigation into fatigue as a dynamic, task-dependent state and into SART performance as an objective measure and inducer of fatigue.

Effects of Back Pressure on the Feasibility and Tolerability of Laryngeal Diadochokinetic Exercise: A Pilot Study

BACKGROUND

The term vocal demand response refers to how speakers meet vocal demands. Vocal loading tasks with predetermined demand parameters (duration, pitch, loudness, etc) have been used in research to study the vocal demand response; these have historically consisted of loud sustained vowel and loud speech tasks. Tasks founded on laryngeal diadochokinesis (LDDK) may be viable alternatives, especially if demand parameters such as exercise-rest ratio and fluid back pressure are concurrently modulated.

OBJECTIVES

To explore the effects of four fluid back pressure conditions (0, 5, 10, and 15 cm H2O) on several measures of subjective participant experience, feasibility, and tolerability during intervallic laryngeal diadochokinetic exercise.

METHODS

Participants (n = 12) completed 15-minute trials of LDDK in 30-second rest and exercise intervals against four counterbalanced back pressure conditions: 0, 5, 10, and 15 cm H2O. The effects of back pressure on (1) ratings of perceived vocal exertion, (2) prevalence of adverse effects such as shortness of breath or lightheadedness, (3) subjective difficulty of sustaining LDDK, (4) number of exercise intervals completed, (5) rankings of participant-preferred back pressure levels, and (6) expert ratings of auditory-perceptual diadochokinetic strength were assessed descriptively.

RESULTS

Perceived vocal exertion, lightheadedness, and subjective laryngeal diadochokinetic difficulty increased as back pressure increased. Number of intervals completed, auditory-perceptual diadochokinetic strength, and participant rankings of back pressure conditions, by contrast, decreased as back pressure increased. 0 and 5 cm H2O were the most preferred back pressure conditions overall.

DISCUSSION

Fluid back pressure was feasible and broadly tolerated during 15-minute trials of vocal exercise. However, the transition from 5 → 10 cm H2O appeared to represent an inflection point in our results: a minority of participants did not tolerate exercise at 10 cm H2O, becoming a majority at 15 cm H2O. We conclude that fluid back pressure should be restricted to values between 0 and 10 cm H2O during LDDK.

Hemodynamic and neuromuscular basis of reduced exercise capacity in patients with end-stage renal disease

PURPOSE

The present study aimed to characterize the exercise-induced neuromuscular fatigue and its possible links with cerebral and muscular oxygen supply and utilization to provide mechanistic insights into the reduced exercise capacity characterizing patients with end-stage renal disease (ESRD).

METHODS

Thirteen patients with ESRD and thirteen healthy males (CTR group) performed a constant-force sustained isometric contraction at 50% of their maximal voluntary isometric contraction (MVC) until exhaustion. Quadriceps muscle activation during exercise was estimated from vastus lateralis, vastus medialis, and rectus femoris EMG. Central and peripheral fatigue were quantified via changes in pre- to postexercise quadriceps voluntary activation (ΔVA) and quadriceps twitch force (ΔQtw,pot) evoked by supramaximal electrical stimulation, respectively. To assess cerebral and muscular oxygenation, throughout exercise, near-infrared spectroscopy allowed investigation of changes in oxyhemoglobin (∆O2Hb), deoxyhemoglobin (∆HHb), and total hemoglobin (∆THb) in the prefrontal cortex and in the vastus lateralis muscle.

RESULTS

ESRD patients demonstrated lower exercise time to exhaustion than that of CTR (88.8 ± 15.3 s and 119.9 ± 14.6 s, respectively, P < 0.01). Following the exercise, MVC, Qtw,pot, and VA reduction were similar between the groups (P > 0.05). There was no significant difference in muscle oxygenation (∆O2Hb) between the two groups (P > 0.05). Cerebral and muscular blood volume (∆THb) and oxygen extraction (∆HHb) were significantly blunted in the ESRD group (P < 0.05). A significant positive correlation was observed between time to exhaustion and cerebral blood volume (∆THb) in both groups (r2 = 0.64, P < 0.01).

CONCLUSIONS

These findings support cerebral hypoperfusion as a factor contributing to the reduction in exercise capacity characterizing ESRD patients.

Effects of Astaxanthin Supplementation on Fatigue, Motor Function and Cognition: A Meta-Analysis of Randomized Controlled Trials

Dietary astaxanthin supplementation has been demonstrated to have many beneficial and health-promoting effects. The purpose of this systematic review and meta-analysis was to assess the effect of astaxanthin supplementation on fatigue, cognition, and exercise efficiency. A total of 11 randomized controlled trials (RCTs) with 346 healthy participants were included. The random effects model and pooled standardized mean difference (SMDs) were used according to Hedge's g for the meta-analysis, and a meta-regression was also conducted. The results of the two existing studies showed a positive trend for astaxanthin in subjective fatigue relief. The effects of astaxanthin supplementation for 8-12 weeks on cognitive accuracy were marginally significant (SMD: .12; 95% CI: -.02-.26) and on reaction time was not significant (SMD: -.08; 95% CI: -.26 to .10). Remarkably, astaxanthin supplementation combined with regular training could enhance the fat oxidation (SMD: 2.56; 95% CI: 1.24-3.89), and significantly improve the physical performance (SMD: .62; 95% CI: .17-1.06). The subgroup analysis further showed significantly greater benefits when performing the aerobic exercises performance (SMD: .45; 95% CI: .13-.76), when the dose was ≥ 20 mg (SMD: .37; 95% CI: .11-.63), and when the supplementation duration was > 12 weeks (SMD: .66; 95% CI: .13-.63). We conclude that astaxanthin supplementation could significantly enhance aerobic exercise efficiency, especially at higher doses and for longer durations. Further studies based on large sample sizes are imperatively warranted.

The telephone-based application of the modified fatigue impact scale in individuals with multiple sclerosis: An investigation of measurement properties

BACKGROUND

Fatigue is one of the most common symptoms reported by individuals with multiple sclerosis and it contributes to the reduction of the functionality. Therefore, it is important to assess the impact of fatigue on daily living of individuals with multiple sclerosis. The Modified Fatigue Impact Scale (MFIS) is an instrument to assess the perception of the impact of fatigue. However, there have been no investigations about the measurement properties of this instrument administered over the telephone for individuals with multiple sclerosis.

OBJECTIVES

To verify the concurrent validity, the test-retest reliability, the standard error of measurement (SEM) and the minimal detectable change (MDC) of the MFIS applied over the telephone to assess the perception of the impact of fatigue of individuals with multiple sclerosis.

METHODS

The MFIS, composed of 21 items covering three domains: physical, cognitive and psychosocial, was applied at three different moments with an interval of 5-7 days. To establish the concurrent criterion validity, the face-to-face application and the first evaluation by telephone were used. The two telephone assessments were used to assess the test-retest reliability The intraclass correlation coefficient (ICC) with 95 % confidence interval (CI) and the Bland-Altman method were used. The standard error of measurement (SEM) and the MDC was calculated according to reliability results.

RESULTS

Thirty individuals (40.83 ± 10.61, 60 % female) were included. The median score on the Expanded Disability Status Scale was 2.00 (±4.00). The majority of participants experienced fatigue (n = 17; 56.67 %). A significant and high magnitude correlation (0.70 ≤ ICC ≤ 0.87, p < 0.001) was found in the investigation of concurrent criterion validity. The Bland-Altman method showed a mean difference between 0.70 to 2.17 points between face-to-face and telephone-based application of the MFIS. For test-retest reliability, a significant and very high magnitude correlation (0.91 ≤ ICC ≤ 0.97, p < 0.001) was found. The Bland-Altman method showed a mean difference between -0.03 and -0.77 points between two telephone-based applications. The SEM and the MDC were 0.71 and 1.97 points.

CONCLUSION

The telephone-based application of the MFIS to assess the perceived impact of fatigue in individuals with multiple sclerosis demonstrated adequate measurement properties, and may be a valuable tool to assess patients in clinical practice.

Clinical and Physiological Variables in Patients with Post-COVID-19 Condition and Persistent Fatigue

Background/Objectives: Post-COVID-19 condition can manifest through various symptoms such as dyspnea, cognitive disturbances, and fatigue, with mechanisms related to these symptoms, particularly those related to fatigue, still requiring further clarification. Therefore, our aim was to assess the clinical and physiological variables in patients with post-COVID-19 condition and persistent fatigue. Methods: After one year post-COVID-19 infection, the patients underwent a comprehensive evaluation, including a complete blood count, a metabolic panel, complete spirometry, and assessments of dyspnea, quality of life, anxiety and depression, physical capacity, body composition, muscle strength, comorbidities, and medications. The participants were categorized into two groups: G1-fatigue and G2-non-fatigue. Results: Seventy-seven patients (53% female; 55 ± 11.8 years) were included, 37 in G1 and 40 in G2. As for clinical markers and symptoms of illness, in those with persistent fatigue symptoms, a greater sensation of dyspnea [BDI score: 7.5 (6-9) vs. 12 (9-12), p < 0.001; mMRC score: 1 (1-2) vs. 0 (0-1), p = 0.002], worse quality of life [SGRQ total score: 1404 (1007-1897) vs. 497 (274-985); p < 0.001], higher levels of anxiety [HADS-A score: 8 (5-9) vs. 3 (0.5-4); p < 0.001], and a reduction in peripheral and inspiratory muscle strength [handgrip strength: 34 (28-40) vs. 40 (30-46.5) kgf, p = 0.044; MIP: -81 ± 31 vs. -111 ± 33 mmHg, p < 0.001)] were observed. Conclusions: Those with persistent fatigue exhibited a greater sensation of dyspnea, higher levels of anxiety, reduced peripheral and inspiratory muscle strength, and a greater impairment of quality of life. The severity of fatigue was influenced by the worsening quality of life, heightened anxiety levels, and decreased peripheral muscle strength. Additionally, the worse quality of life was associated with a higher sensation of dyspnea, lower muscle strength, and reduced physical capacity.

Myasthenia gravis: the future is here

Myasthenia gravis (MG) stands as a prototypical antibody-mediated autoimmune disease: it is dependent on T cells and characterized by the presence of autoantibodies targeting proteins located on the postsynaptic surface of skeletal muscle, known as the neuromuscular junction. Patients with MG exhibit a spectrum of weakness, ranging from limited ocular muscle involvement to life-threatening respiratory failure. Recent decades have witnessed substantial progress in understanding the underlying pathophysiology, leading to the delineation of distinct subcategories within MG, including MG linked to AChR or MuSK antibodies as well as age-based distinction, thymoma-associated, and immune checkpoint inhibitor-induced MG. This heightened understanding has paved the way for the development of more precise and targeted therapeutic interventions. Notably, the FDA has recently approved therapeutic inhibitors of complement and the IgG receptor FcRn, a testament to our improved comprehension of autoantibody effector mechanisms in MG. In this Review, we delve into the various subgroups of MG, stratified by age, autoantibody type, and histology of the thymus with neoplasms. Furthermore, we explore both current and potential emerging therapeutic strategies, shedding light on the evolving landscape of MG treatment.

Connecting the dots: the role of fatigue in female infertility

Fatigue, an increasingly acknowledged symptom in various chronic diseases, has garnered heightened attention, during the medical era of bio-psycho-social model. Its persistence not only significantly compromises an individual's quality of life but also correlates with chronic organ damage. Surprisingly, the intricate relationship between fatigue and female reproductive health, specifically infertility, remains largely unexplored. Our exploration into the existing body of evidence establishes a compelling link between fatigue with uterine and ovarian diseases, as well as conditions associated with infertility, such as rheumatism. This observation suggests a potentially pivotal role of fatigue in influencing overall female fertility. Furthermore, we propose a hypothetical mechanism elucidating the impact of fatigue on infertility from multiple perspectives, postulating that neuroendocrine, neurotransmitter, inflammatory immune, and mitochondrial dysfunction resulting from fatigue and its co-factors may further contribute to endocrine disorders, menstrual irregularities, and sexual dysfunction, ultimately leading to infertility. In addition to providing this comprehensive theoretical framework, we summarize anti-fatigue strategies and accentuate current knowledge gaps. By doing so, our aim is to offer novel insights, stimulate further research, and advance our understanding of the crucial interplay between fatigue and female reproductive health.

Force and Neuromuscular Responses During a Handgrip Hold to Failure Anchored to a Moderate Perceptual Intensity in Males

OBJECTIVES

The current study investigated performance fatigability (PF) and time course of changes in force, electromyographic amplitude (EMG AMP) and frequency (EMG MPF), and neuromuscular efficiency (NME) during a sustained, isometric, handgrip hold to failure (HTF) using the rating of perceived exertion (RPE)-Clamp Model.

METHODS

Twelve males performed a handgrip HTF anchored to RPE=5. The time to task failure (Tlim), force (N), EMG AMP and MPF, and NME (normalized force/ normalized EMG AMP) were recorded. Analyses included a paired samples t-test for PF at an alpha of p<0.05, 1-way repeated measures ANOVA across time and post-hoc t-tests (p<0.0025) for force, EMG AMP and MPF, and NME responses.

RESULTS

The PF (pre- to post- maximal force % decline) was 38.2±11.5%. There were decreases in responses, relative to 0% Tlim, from 40% to 100% Tlim (force), at 30%, 60%, and 100% Tlim (EMG AMP), from 10% to 100% Tlim(EMP MPF), and from 50% to 65%, and 80% to 100% Tlim (NME) (p<0.0025).

CONCLUSIONS

The RPE-Clamp Model in this study demonstrated that pacing strategies may be influenced by the integration of anticipatory, feedforward, and feedback mechanisms, and provided insights into the relationship between neuromuscular and perceptual responses, and actual force generating capacity.

Sleep-wake behavior, perceived fatigability, and cognitive reserve in older adults

INTRODUCTION

The effects of sleep-wake behavior on perceived fatigability and cognitive abilities when performing daily activities have not been investigated across levels of cognitive reserve (CR).

METHODS

CR Index Questionnaire (CRIq) data were collected and subjected to moderated mediation analysis.

RESULTS

In amnestic mild cognitive impairment (aMCI; n = 41), CR moderated sleep-related impairments (SRIs), and fatigability at low CR (CRIq < 105.8, p = 0.004) and mean CR (CRIq = 126.9, p = 0.03) but not high CR (CRIq > 145.9, p = 0.65) levels. SRI affected cognitive abilities mediated by fatigability at low CR (p < 0.001) and mean CR (p = 0.003) levels. In healthy controls (n = 13), SRI in fatigability did not alter cognitive abilities across CR levels; controls had higher leisure scores than patients with aMCI (p = 0.003, effect size = 0.93).

DISCUSSION

SRI can amplify impaired cognitive abilities through exacerbation of fatigability in patients with aMCI with below-mean CR. Therefore, improving sleep-wake regulation and leisure activities may protect against fatigability and cognitive decline.

HIGHLIGHTS

Clinical fatigue and fatigability cannot be alleviated by rest. Clinical fatigability disrupts daily activities during preclinical Alzheimer's. High cognitive reserve mitigates sleep-wake disturbance effects. High cognitive reserve attenuates clinical fatigability effects on daily functioning. Untreated obstructive sleep apnea potentiates Alzheimer's pathology in the brain.

A Biopsychosocial Model for Understanding Training Load, Fatigue, and Musculoskeletal Sport Injury in University Athletes: A Scoping Review

ABSTRACT

McClean, ZJ, Pasanen, K, Lun, V, Charest, J, Herzog, W, Werthner, P, Black, A, Vleuten, RV, Lacoste, E, and Jordan, MJ. A biopsychosocial model for understanding training load, fatigue, and musculoskeletal sport injury in university athletes: A scoping review. J Strength Cond Res 38(6): 1177-1188, 2024-The impact of musculoskeletal (MSK) injury on athlete health and performance has been studied extensively in youth sport and elite sport. Current research examining the relationship between training load, injury, and fatigue in university athletes is sparse. Furthermore, a range of contextual factors that influence the training load-fatigue-injury relationship exist, necessitating an integrative biopsychosocial model to address primary and secondary injury prevention research. The objectives of this review were (a) to review the scientific literature examining the relationship between training load, fatigue, and MSK injury in university athletes and (b) to use this review in conjunction with a transdisciplinary research team to identify biopsychosocial factors that influence MSK injury and develop an updated, holistic biopsychosocial model to inform injury prevention research and practice in university sport. Ten articles were identified for inclusion in this review. Key findings were an absence of injury surveillance methodology and contextual factors that can influence the training load-fatigue-MSK injury relationship. We highlight the inclusion of academic load, social load, and mental health load as key variables contributing to a multifactorial, gendered environmental, scientific inquiry on sport injury and reinjury in university sport. An integrative biopsychosocial model for MSK injury in university sport is presented that can be used to study the biological, psychological, and social factors that modulate injury and reinjury risk in university athletes. Finally, we provide an example of how causal inference can be used to maximize the utility of longitudinally collected observational data that is characteristic of sport performance research in university sport.

Clinical and neuroanatomical predictors of post-stroke fatigue

INTRODUCTION

Post-stroke fatigue (PSF) has been described as early exhaustion with tiredness that develops during physical or mental activity and generally does not improve with rest. There are inconsistent findings on the relationship between the characteristics of the ischemic brain lesion and PSF. However, some studies suggest that specific neuroanatomical and neuroplastic changes could explain post-stroke fatigue. The aim was to evaluate the severity of PSF in relation to the location and the size of the ischemic lesion in acute stroke patients to establish possible predictors of PSF.

PATIENTS AND METHODS

We performed a prospective observational study to establish potential early predictors of long-term PSF, which was assessed using the Fatigue Assessment Scale six months after ischemic stroke. After segmenting brain infarcts on Diffusion-Weighted Imaging (DWI) images, we studied the association with PSF using Voxel-Based Lesion-Symptom Mapping (VLSM).

RESULTS

Out of 104 patients, 61 (59 %) reported PSF. Female sex and history of diabetes mellitus were associated with a greater risk of developing PSF. The association of PSF with female sex was confirmed in a replication cohort of 50 patients. The ischemic lesion volume was not associated with PSF, and VBLSM analysis did not identify any specific brain area significantly associated with PSF.

CONCLUSIONS

PSF is frequent in stroke patients, especially women, even after six months. The absence of neuroanatomical correlates of PSF suggests that it is a multifactorial process with biological, psychological, and social risk factors that require further study.

Are performance and perceived fatigability dependent on the anchor scheme of fatiguing isometric tasks in men?

BACKGROUND

Ratings of perceived exertion (RPE) can be used to regulate exercise intensity. This study examined the effect of anchor scheme on performance fatigability and neuromuscular responses following fatiguing forearm flexion tasks.

METHODS

Twelve men (age 20.9±2.2 years; height 179.8±5.3 cm; body mass 80.2±9.9 kg) performed sustained, isometric forearm flexion tasks to failure anchored to RPE=6 (RPEFT) and the torque (TRQFT) that corresponded to RPE=6. Pre-test and post-test maximal voluntary isometric contractions (MVIC) were performed to quantify changes in the amplitude (AMP) and mean power frequency (MPF) of the electromyographic (EMG) and mechanomyographic (MMG) signals. Neuromuscular efficiency (NME) was calculated by dividing normalized torque by normalized EMG AMP. A dependent t-test was used to assess the mean difference for time to task failure (TTF). Repeated measures ANOVAs were used to compare mean differences for performance fatigability and normalized neuromuscular parameters.

RESULTS

The RPEFT had a greater TTF than the TRQFT (P<0.001). MVIC and NME decreased from pre-test to post-test following the RPEFT and TRQFT (P<0.05) with no differences between anchor schemes. Following the TRQFT, normalized EMG MPF decreased from pre-test to post-test (P=0.004). Following the RPEFT, normalized MMG MPF increased from pre-test to post-test (P=0.021). There were no changes in normalized EMG AMP or MMG AMP (P>0.05).

CONCLUSIONS

These findings indicated anchor scheme-specific neuromuscular responses and TTF, despite no difference in performance fatigability. Furthermore, performance fatigability was likely due to peripheral fatigue (based on normalized EMG MPF and NME) following the TRQFT, but peripheral and central fatigue (based on normalized MMG MPF and NME) following the RPEFT.

Associations of depression and perceived physical fatigability with white matter integrity in older adults

BACKGROUNDS

Fatigability is prevalent in older adults. However, it is often associated with depressed mood. We aim to investigate these two psychobehavioral constructs by examining their underpinning of white matter structures in the brain and their associations with different medical conditions.

METHODS

Twenty-seven older adults with late-life depression (LLD) and 34 cognitively normal controls (CN) underwent multi-shell diffusion MRI. Fatigability was measured with the Pittsburgh Fatigability Scale. We examined white matter integrity by measuring the quantitative anisotropy (QA), a fiber tracking parameter with better accuracy than the traditional imaging technique.

RESULTS

We found those with LLD had lower QA in the 2nd branch of the left superior longitudinal fasciculus (SLF-II), and those with more physical fatigability had lower QA in more widespread brain regions. In tracts associated with more physical fatigability, the lower QA in left acoustic radiation and left superior thalamic radiation correlated with higher blood glucose (r = - 0.46 and - 0.49). In tracts associated with depression, lower QA in left SLF-II correlated with higher bilirubin level (r = - 0.58).

DISCUSSION

Depression and fatigability were associated with various white matter integrity changes, which correlated with biochemistry biomarkers all related to inflammation.