Translating Fatigue to Human Performance

Limits of Ultra: Towards an Interdisciplinary Understanding of Ultra-Endurance Running Performance

Ultra-endurance running (UER) poses extreme mental and physical challenges that present many barriers to completion, let alone performance. Despite these challenges, participation in UER events continues to increase. With the relative paucity of research into UER training and racing compared with traditional endurance running distance (e.g., marathon), it follows that there are sizable improvements still to be made in UER if the limitations of the sport are sufficiently understood. The purpose of this review is to summarise our current understanding of the major limitations in UER. We begin with an evolutionary perspective that provides the critical background for understanding how our capacities, abilities and limitations have come to be. Although we show that humans display evolutionary adaptations that may bestow an advantage for covering large distances on a daily basis, these often far exceed the levels of our ancestors, which exposes relative limitations. From that framework, we explore the physiological and psychological systems required for running UER events. In each system, the factors that limit performance are highlighted and some guidance for practitioners and future research are shared. Examined systems include thermoregulation, oxygen delivery and utilisation, running economy and biomechanics, fatigue, the digestive system, nutritional and psychological strategies. We show that minimising the cost of running, damage to lower limb tissue and muscle fatigability may become crucial in UER events. Maintaining a sustainable core body temperature is critical to performance, and an even pacing strategy, strategic heat acclimation and individually calculated hydration all contribute to sustained performance. Gastrointestinal issues affect almost every UER participant and can be due to a variety of factors. We present nutritional strategies for different event lengths and types, such as personalised and evidence-based approaches for varying types of carbohydrate, protein and fat intake in fluid or solid form, and how to avoid flavour fatigue. Psychology plays a vital role in UER performance, and we highlight the need to be able to cope with complex situations, and that specific long and short-term goal setting improves performance. Fatigue in UER is multi-factorial, both physical and mental, and the perceived effort or level of fatigue have a major impact on the ability to continue at a given pace. Understanding the complex interplay of these limitations will help prepare UER competitors for the different scenarios they are likely to face. Therefore, this review takes an interdisciplinary approach to synthesising and illuminating limitations in UER performance to assist practitioners and scientists in making informed decisions in practice and applicable research.

Analysing experienced and inexperienced cyclists' attentional focus and self-regulatory strategies during varying intensities of fixed perceived effort cycling: A mixed method study

Using a think aloud approach during fixed perceived effort exercise is a unique method to explore the decision-making processes that guide the self-regulation of perceived effort during endurance-based activity. In a two-part study, authors investigated the attentional focus and self-regulatory strategies associated with: Part A - perceived effort corresponding to (RPEGET) and above gas exchange threshold (RPE+15%GET); Part B - between experienced and inexperienced cyclists during fixed perceived effort cycling tasks. Eighteen (15 male, 3 female) healthy, active individuals completed three visits (visit 1 - ramped incremental test and familiarisation, visit 2 and 3-30-min fixed perceived effort cycling). During which, power output, heart rate, lactate, think aloud, and perceptual markers were taken. Random-intercepts linear mixed-effects models assessed the condition, time, and condition × time interactions on all dependent variables. Power output, heart rate, lactate and instances of internal sensory monitoring (t195=2.57,p=.011,β=0.95[0.23,1.68]) and self-regulation (t195=4.14,p=.001,β=1.69[0.89,2.49]) were significantly higher in the RPE+15%GET versus RPEGET trial. No significant differences between inexperienced and experienced cyclists for internal sensory monitoring (t196=-1.78,p=.095,β=-1.73[-3.64,0.18]) or self-regulatory thoughts (t196=-0.39,p=.699,β=-1.06[-6.32,4.21]) were noted but there were significant condition × time interactions for internal monitoring (t196=2.02,p=.045,β=0.44[0.01,0.87]) and self-regulation (t196=3.45,p=.001,β=0.85[0.37,1.33]). Seemingly, experienced athletes associatively attended to internal psychophysiological state and subsequently self-regulate their psychophysiological state at earlier stages of exercise than inexperienced athletes. This is the first study to exhibit the differences in attentional focus and self-regulatory strategies that are activated based on perceived effort intensity and experience level in cyclists.

Reliability of isokinetic decay slope is superior to using fatigue indices for shoulder horizontal abduction

INTRODUCTION

Reliable and valid measurements for shoulder muscular endurance should be available for clinical use. The posterior shoulder endurance test offers a potential clinical assessment, but its construct validity isn't available. Since a criterion measure of muscular endurance is not available, this study's purpose was to determine a reliable method for testing shoulder muscular endurance using an isokinetic dynamometer.

METHODS

The test-retest reliability, standard error measurement, and minimal detectable change were calculated on four different paradigms to quantify muscular fatigue using two isokinetic speeds (60°sec-1,180°sec-1). Calculation paradigms included peak torque fatigue index (FI), average torque FI, area-under-the-curve FI, and peak torque decay slope. Testing occurred on two days. Repeated measures analysis of variance compared the two peak torque decay slopes across both testing days.

RESULTS

Superior reliability was found within the decay slope measurements at both 60°sec-1 (ICC = 0.941) and 180°sec-1 (ICC = 0.764) speeds, with the 60°sec-1 decay slope being the highest reliability between the two angular velocities. There was a greater amount of fatigue in the 60°sec-1 decay slope compared to the 180°sec-1 decay slope.

CONCLUSION

Using the decay slope of isokinetic shoulder horizontal abduction at 60°sec-1 is a reliable method to validate other muscular endurance clinical measures. Rehabilitation specialists should utilize the decay slope of the isokinetic dynamometry to monitor responsiveness.

Decreased neural drive affects the early rate of force development after repeated burst-like isometric contractions

The neural drive to the muscle is the primary determinant of the rate of force development (RFD) in the first 50 ms of a rapid contraction. It is still unproven if repetitive rapid contractions specifically impair the net neural drive to the muscles. To isolate the fatiguing effect of contraction rapidity, 17 male adult volunteers performed 100 burst-like (i.e., brief force pulses) isometric contractions of the knee extensors. The response to electrically-evoked single and octet femoral nerve stimulation was measured with high-density surface electromyography (HD-sEMG) from the vastus lateralis and medialis muscles. Root mean square (RMS) of each channel of HD-sEMG was normalized to the corresponding M-wave peak-to-peak amplitude, while muscle fiber conduction velocity (MFCV) was normalized to M-wave conduction velocity to compensate for changes in sarcolemma properties. Voluntary RFD 0-50 ms decreased (d = -0.56, p < 0.001) while time to peak force (d = 0.90, p < 0.001) and time to RFDpeak increased (d = 0.56, p = 0.034). Relative RMS (d = -1.10, p = 0.006) and MFCV (d = -0.53, p = 0.007) also decreased in the first 50 ms of voluntary contractions. Evoked octet RFD 0-50 ms (d = 0.60, p = 0.020), M-wave amplitude (d = 0.77, p = 0.009) and conduction velocity (d = 1.75, p < 0.001) all increased. Neural efficacy, i.e., voluntary/octet force ratio, largely decreased (d = -1.50, p < 0.001). We isolated the fatiguing impact of contraction rapidity and found that the decrement in RFD, particularly when calculated in the first 50 ms of muscle contraction, can mainly be explained by a decrease in the net neural drive.

Polysaccharides derived from natural edible and medicinal sources as agents targeting exercise-induced fatigue: A review

Exercise-induced fatigue (EF) is a common occurrence during prolonged endurance and excessive exercise and is mainly caused by energy depletion, harmful metabolite accumulation, oxidative stress, and inflammation. EF usually leads to a reduction in initiating or maintaining spontaneous activities and muscle performance and ultimately results in a decrease in the quality of life of people who engage in physical work. Therefore, the interest in investigating EF-targeting agents with minimal side effects and good long-term efficacy has substantially increased. Natural edible and medicinal polysaccharides have shown positive anti-EF effects, but the relevant reviews are rare. This review comprehensively summarizes studies on natural polysaccharides from edible and medicinal sources that can relieve EF and improve physical performance from the past decade, focusing on their sources, monosaccharide compositions, anti-EF effects, and possible molecular mechanisms. Most of these anti-EF polysaccharides are heteropolysaccharides and are mainly composed of glucose, arabinose, galactose, rhamnose, xylose, and mannose. In EF animal models, the polysaccharides exert positive EF-alleviating effects through energy supply, metabolic regulation, antioxidation, anti-inflammation, and gut microbiota remodeling. However, further studies are still needed to clarify the anti-EF effects of these polysaccharides on human beings. In summary, the present review expects to provide scientific data for the future research and development of natural polysaccharide-based anti-EF drugs, dietary supplements, and health-care products for specific fatigue groups.

Acute effects of static balance exercise combined with different levels of blood flow restriction on motor performance fatigue as well as physiological and perceptual responses in young healthy males and females

PURPOSE

This study investigated the acute effects of a static balance exercise combined with different blood flow restriction (BFR) pressures on motor performance fatigue development and recovery as well as physiological and perceptual responses during exercise in males and females.

METHODS

Twenty-four recreational active males (n = 13) and females (n = 11) performed static balance exercise on a BOSU ball (3 sets of 60 s with 30 s rest in-between) on three separate (> 3 days) laboratory visits with three different BFR pressures (80% arterial occlusion pressure [AOP], 40%AOP, 30 mmHg [SHAM]) in random order. During exercise, activity of various leg muscles, vastus lateralis muscle oxygenation, and ratings of effort and pain perception were recorded. Maximal squat jump height was measured before, immediately after, 1, 2, 4, and 8 min after exercise to quantify motor performance fatigue development and recovery.

RESULTS

Quadriceps muscle activity as well as ratings of effort and pain were highest, while muscle oxygenation was lowest in the 80%AOP compared to the 40%AOP and SHAM condition, with no differences in postural sway between conditions. Squat jump height declined after exercise with the highest reduction in the 80%AOP (- 16.4 ± 5.2%) followed by the 40%AOP (- 9.1 ± 3.2%), and SHAM condition (- 5.4 ± 3.3%). Motor performance fatigue was not different after 1 min and 2 min of recovery in 40% AOP and 80% AOP compared to SHAM, respectively.

CONCLUSION

Static balance exercise combined with a high BFR pressure induced the largest changes in physiological and perceptual responses, without affecting balance performance. Although motor performance fatigue was increased by BFR, it may not lead to long-term impairments in maximal performance.

Perceived cognitive fatigue has only marginal effects on static balance control in healthy young adults

We examined the influence of perceived cognitive fatigue on static balance control in healthy young adults to gain greater clarity about this issue than provided in previous research. Based on the prevailing assumption in pertinent literature, we hypothesized that the influence of cognitive fatigue on balance control depends on the attentional effort required by the balance tasks being performed. To test this hypothesis, 44 young adults (24 women and 20 men) were alternately assigned to either the experimental group that was cognitively fatigued (using the 16-min TloadDback-task with individualized settings) or the control group (who watched a documentary). Before and after the intervention, the participants performed six balance tasks that differed in (attentional) control requirements, while recording the center of pressure (COP). From these time series, sway variability, mean speed, and sample entropy were calculated and analyzed statistically. Additionally, perceived cognitive fatigue was assessed using VAS scales. Statistical analyses confirmed that the balance tasks differed in control characteristics and that cognitive fatigue was elevated in the experimental group, but not in the control group. Nevertheless, no significant main effects of cognitive fatigue were found on any of the COP measures of interest, except for some non-robust interaction effects related primarily to sample entropy. These results suggest that, in young adults, postural control in static balance tasks is largely automatic and unaffected by task-induced state fatigue.

The measurement of fatigue in clinicians within hospital settings: A systematic review of measurement properties

Medical staff fatigue leads to accidents and mistakes and puts patient safety at risk. A measure of fatigue in the workplace may help to quantify, predict, and manage fatigue. This review aimed to evaluate instruments used to measure fatigue in medical staff within hospitals. A systematic review following the JBI methodology was undertaken. A search for articles was conducted in 2021. Included articles (all validation studies) were assessed for methodological quality using the COSMIN checklist. Measurement property data was evaluated for Quality of Evidence using GRADE methodology. Ten studies representing five instruments were reviewed: Occupational Fatigue Exertion and Recovery scale (now superseded); Occupational Fatigue Exertion and Recovery scale (15-item); Multidimensional Fatigue Inventory; Need for Recovery Scale; and the Swedish Occupational Fatigue Inventory. Four instruments show promise for measuring fatigue in hospital medical staff, however, there is limited certainty in the measure property estimates. The Quality of Evidence for measurement properties for all instruments is insufficient. Further validation studies following the COSMIN standards are needed before recommendations for use can be made.

The role of clinical neurophysiology in the definition and assessment of fatigue and fatigability

Though a common symptom, fatigue is difficult to define and investigate, occurs in a wide variety of neurological and systemic disorders, with differing pathological causes. It is also often accompanied by a psychological component. As a symptom of long-term COVID-19 it has gained more attention. In this review, we begin by differentiating fatigue, a perception, from fatigability, quantifiable through biomarkers. Central and peripheral nervous system and muscle disorders associated with these are summarised. We provide a comprehensive and objective framework to help identify potential causes of fatigue and fatigability in a given disease condition. It also considers the effectiveness of neurophysiological tests as objective biomarkers for its assessment. Among these, twitch interpolation, motor cortex stimulation, electroencephalography and magnetencephalography, and readiness potentials will be described for the assessment of central fatigability, and surface and needle electromyography (EMG), single fibre EMG and nerve conduction studies for the assessment of peripheral fatigability. The purpose of this review is to guide clinicians in how to approach fatigue, and fatigability, and to suggest that neurophysiological tests may allow an understanding of their origin and interactions. In this way, their differing types and origins, and hence their possible differing treatments, may also be defined more clearly.

Association between COVID-19 and outstanding academic performance at a Spanish university

BACKGROUND

SARS-CoV-2 is the causative agent of COVID-19 identified in December 2019, an acute infectious respiratory disease that can cause persistent neurological and musculoskeletal symptoms such as headache, fatigue, myalgias difficulty concentrating, among others including acute cerebrovascular disease with a prevalence of 1-35%. The aim of this study is to evaluate the impact of COVID-19 in undergraduate students on their academic performance as an indicator of their intellectual ability and performance in a university that maintained 100% face-to-face teaching during the 2020-2021 academic year.

METHODS

A total of 7,039 undergraduate students were analyzed in a prospective cohort study at the University of Navarra. A questionnaire including sociodemographic and behavioral questions was sent. PCRs were performed throughout the academic year for the diagnosis of SARS-CoV-2 infection and students' academic results were provided by the academic center, adjusted descriptive and multivariate models were performed to assess the association.

RESULTS

A total of 658 (9.3%) participants were diagnosed with COVID-19, almost 4.0% of them achieved outstanding academic results, while uninfected students did so in 7.3%. SARS-CoV-2 infection was associated with a significant decrease in having outstanding academic results (OR = 0.57; 95% CI: 0.38-0.86).

CONCLUSION

Having COVID-19 disease, decreased academic performance in undergraduate students. Therefore, it is necessary to prevent infection even in the youngest sections of the population.

Sleep, Nutrition, and Injury Risk in Adolescent Athletes: A Narrative Review

This narrative review explores the impact of sleep and nutrition on injury risk in adolescent athletes. Sleep is viewed as essential to the recuperation process and is distinguished as an active participant in recovery through its involvement in growth, repair, regeneration, and immunity. Furthermore, the literature has shown that the sleep of athletes impacts elements of athletic performance including both physical and cognitive performance, recovery, injury risk, and mental well-being. For sleep to have a restorative effect on the body, it must meet an individual's sleep needs whilst also lasting for an adequate duration and being of adequate quality, which is age-dependent. The literature has suggested that athletes have increased sleep needs compared to those of the general population and thus the standard recommendations may not be sufficient for athletic populations. Therefore, a more individualised approach accounting for overall sleep health may be more appropriate for addressing sleep needs in individuals including athletes. The literature has demonstrated that adolescent athletes achieve, on average, ~6.3 h of sleep, demonstrating a discrepancy between sleep recommendations (8-10 h) and actual sleep achieved. Sleep-wake cycles undergo development during adolescence whereby adaptation occurs in sleep regulation during this phase. These adaptations increase sleep pressure tolerance and are driven by the maturation of physiological, psychological, and cognitive functioning along with delays in circadian rhythmicity, thus creating an environment for inadequate sleep during adolescence. As such, the adolescent period is a phase of rapid growth and maturation that presents multiple challenges to both sleep and nutrition; consequently, this places a significant burden on an adolescent athletes' ability to recover, thus increasing the likelihood of injury. Therefore, this article aims to provide a comprehensive review of the available literature on the importance of sleep and nutrition interactions in injury risk in adolescent athletes. Furthermore, it provides foundations for informing further investigations exploring the relation of sleep and nutrition interactions to recovery during adolescence.

Behavioral and physiological fatigue-related factors influencing timing and force control learning in pianists

Optimizing the training regimen depending on neuromuscular fatigue is crucial for the well-being of professionals intensively practicing motor skills, such as athletes and musicians, as persistent fatigue can hinder learning and cause neuromuscular injuries. However, accurate assessment of fatigue is challenging because of the dissociation between subjective perception and its impact on motor and cognitive performance. To address this issue, we investigated the interplay between fatigue and learning development in 28 pianists during three hours of auditory-motor training, dividing them into two groups subjected to different resting conditions. Changes in behavior and muscle activity during training were measured to identify potential indicators capable of detecting fatigue before subjective awareness. Our results indicate that motor learning and fatigue development are independent of resting frequency and timing. Learning indices, such as reduction in force and timing errors throughout training, did not differ between the groups. No discernible distinctions emerged in fatigue-related behavioral and physiological indicators between the groups. Regression analysis revealed that several fatigue-related indicators, such as tapping speed variability and electromyogram amplitude per unit force, could explain the learning of timing and force control. Our findings suggest the absence of a universal resting schedule for optimizing auditory-motor learning.

Wrist Extensor Muscle Fatigue During a Dual Task With Two Muscular and Cognitive Load Levels in Younger and Older Adults

OBJECTIVE

To examine the effect of concurrent physical and cognitive demands as well as age on indicators of muscle fatigue at the wrist.

BACKGROUND

There are few studies examining risk indicators for musculoskeletal disorders associated with work-related physical and cognitive demands that often occur simultaneously in the workplace.

METHODS

Twenty-four gender-balanced older and 24 gender-balanced younger (mean age 60 and 23 years) participants performed four 30 min dual tasks. Tasks differed by the muscular load level during force tracking: 5% and 10% of maximum voluntary contraction force (MVC) and concurrent cognitive demands on the working memory: easy and difficult. Muscle fatigue was assessed by MVC decline and changes in surface electromyography (increased root mean square: RMS, decreased median frequency: MF) at the extensor digitorum (ED) and extensor carpi ulnaris (EU).

RESULTS

A decline in MVC was found in all participants when tracking was performed at 10% MVC (mean ± SD: 137.9 ± 49.2 - 123.0 ± 45.3 N). Irrespective of age, muscular, or cognitive load, RMS increased (ED 12.3 ± 6.5 - 14.1 ± 7.0% MVE, EU 15.4 ± 7.6 - 16.9 ± 8.6% MVE) and MF decreased (ED 85.4 ± 13.6 - 83.2 ± 12.8 Hz, EU 107.2 ± 17.1 - 104.3 ± 16.7 Hz) in both muscles. However, changes in MF of EU tended to be more pronounced in the older group at higher cognitive and lower muscular load, without reaching statistical significance.

CONCLUSION

Maximum voluntary contraction indicated no interaction between muscle fatigue, cognitive load, or age. However, the tendencies toward altered muscle activity due to an increase in cognitive load and older age suggest muscular adaptations while maintaining tracking performance during the onset of fatigue signs in the sEMG signal.

APPLICATION

If the tendencies in muscle activity are confirmed by further studies, ergonomic assessments in industrial workplaces should consider cognitive load and age when describing the risk of musculoskeletal disorders.

Maximizing plyometric training for adolescents: a meta-analysis of ground contact frequency and overall intervention time on jumping ability: a systematic review and meta-analysis

Plyometric training boosts adolescents' jumping ability, crucial for athletic success and health. However, the best total ground contact frequency (TGCF) and overall intervention time (OIT) for these exercises remain unclear. This meta-analysis aims to identify optimal TGCF and OIT in plyometric training for adolescents, focusing on countermovement jump (CMJ) and squat jump (SJ) outcomes. This systematic review encompassed five databases and included 38 studies with 50 randomized controlled experiments and 3347 participants. We used the Cochrane risk assessment tool for study quality and Review Manager 5.4 for data analysis. The current meta-analysis incorporated a total of 38 studies, comprising 50 sets of randomized controlled trials, to investigate the influence of different TGCFs and OITs on plyometric training. The Cochrane risk assessment tool indicated that all the included studies were classified as low risk. Various TGCFs in plyometric training positively affected CMJ and SJ heights in adolescents. The TGCF of less than 900 was ideal for enhancing CMJ, whereas more than 1400 was effective for SJ. The optimal OIT was 400-600 min, specifically, 500-600 min for CMJ and 400-500 min for SJ. Plyometric training improves jumping ability in adolescents. Lower ground contact frequency (< 900 contacts) enhances CMJ, while higher ground contact frequency (> 1400 contacts) is more effective for SJ. Optimal intervention time ranges from 400 to 600 min, with 500 to 600 min benefiting CMJ and 400 to 500 min improving SJ.

Alteration of skeletal muscle energy metabolism assessed by phosphorus-31 magnetic resonance spectroscopy in clinical routine, part 1: Advanced quality control pipeline

Implementing a standardized phosphorus-31 magnetic resonance spectroscopy (31 P-MRS) dynamic acquisition protocol to evaluate skeletal muscle energy metabolism and monitor muscle fatigability, while being compatible with various longitudinal clinical studies on diversified patient cohorts, requires a high level of technicality and expertise. Furthermore, processing data to obtain reliable results also demands a great degree of expertise from the operator. In this two-part article, we present an advanced quality control approach for data acquired using a dynamic 31 P-MRS protocol. The aim is to provide decision support to the operator to assist in data processing and obtain reliable results based on objective criteria. We present here, in part 1, an advanced data quality control (QC) approach of a dynamic 31 P-MRS protocol. Part 2 is an impact study that will demonstrate the added value of the QC approach to explore data derived from two clinical populations that experience significant fatigue, patients with coronavirus disease 2019 and multiple sclerosis. In part 1, 31 P-MRS was performed using 3-T clinical MRI in 175 subjects from clinical and healthy control populations conducted in a University Hospital. An advanced data QC score (QCS) was developed using multiple objective criteria. The criteria were based on current recommendations from the literature enriched by new proposals based on clinical experience. The QCS was designed to indicate valid and corrupt data and guide necessary objective data editing to extract as much valid physiological data as possible. Dynamic acquisitions using an MR-compatible ergometer ran over a rest (40 s), exercise (2 min), and a recovery phase (6 min). Using QCS enabled rapid identification of subjects with data anomalies, allowing the user to correct the data series or reject them partially or entirely, as well as identify fully valid datasets. Overall, the use of the QCS resulted in the automatic classification of 45% of the subjects, including 58 participants who had data with no criterion violation and 21 participants with violations that resulted in the rejection of all dynamic data. The remaining datasets were inspected manually with guidance, allowing acceptance of full datasets from an additional 80 participants and recovery phase data from an additional 16 subjects. Overall, more anomalies occurred with patient data (35% of datasets) compared with healthy controls (15% of datasets). In conclusion, the QCS ensures a standardized data rejection procedure and rigorous objective analysis of dynamic 31 P-MRS data obtained from patients. This methodology contributes to efforts made to standardize 31 P-MRS practices that have been underway for a decade, with the goal of making it an empowered tool for clinical research.

Alteration of skeletal muscle energy metabolism assessed by 31 P MRS in clinical routine: Part 2. Clinical application

In this second part of a two-part paper, we intend to demonstrate the impact of the previously proposed advanced quality control pipeline. To understand its benefit and challenge the proposed methodology in a real scenario, we chose to compare the outcome when applying it to the analysis of two patient populations with significant but highly different types of fatigue: COVID-19 and multiple sclerosis (MS). 31 P-MRS was performed on a 3 T clinical MRI, in 19 COVID-19 patients, 38 MS patients, and 40 matched healthy controls. Dynamic acquisitions using an MR-compatible ergometer ran over a rest (40 s), exercise (2 min), and a recovery phase (6 min). Long and short TR acquisitions were also made at rest for T1 correction. The advanced data quality control pipeline presented in Part 1 is applied to the selected patient cohorts to investigate its impact on clinical outcomes. We first used power and sample size analysis to estimate objectively the impact of adding the quality control score (QCS). Then, comparisons between patients and healthy control groups using the validated QCS were performed using unpaired t tests or Mann-Whitney tests (p < 0.05). The application of the QCS resulted in increased statistical power, changed the values of several outcome measures, and reduced variability (standard deviation). A significant difference was found between the T1PCr and T1Pi values of MS patients and healthy controls. Furthermore, the use of a fixed correction factor led to systematically higher estimated concentrations of PCr and Pi than when using individually corrected factors. We observed significant differences between the two patient populations and healthy controls for resting [PCr]-MS only, [Pi ], [ADP], [H2 PO4 - ], and pH-COVID-19 only, and post-exercise [PCr], [Pi ], and [H2 PO4 - ]-MS only. The dynamic indicators τPCr , τPi , ViPCr , and Vmax were reduced for COVID-19 and MS patients compared with controls. Our results show that QCS in dynamic 31 P-MRS studies results in smaller data variability and therefore impacts study sample size and power. Although QCS resulted in discarded data and therefore reduced the acceptable data and subject numbers, this rigorous and unbiased approach allowed for proper assessment of muscle metabolites and metabolism in patient populations. The outcomes include an increased metabolite T1 , which directly affects the T1 correction factor applied to the amplitudes of the metabolite, and a prolonged τPCr , indicating reduced muscle oxidative capacity for patients with MS and COVID-19.

The effects of hand dominance, fatigue, and sex on muscle activation during a repetitive overhead fatiguing task

Previous studies have shown that the dominant arm is generally stronger and more resistant to fatigue. However, whether there are side differences in shoulder muscle activation during a fatiguing upper limb task, and whether this varies according to sex, is unknown. Thirty right-handed adults (15 females) were recruited to complete two sessions of an overhead repetitive fatiguing task (shoulder flexion between 90 and 135° at 1 Hz), performed in two separate sessions with their dominant arm (DA) and non-dominant arm (NDA) until exhaustion. Electromyographic (EMG) data was collected from 11 shoulder muscles of the moving arm, and their activation amplitude (RMS) and activation variability (SD) were assessed. Results show that time to exhaustion was not affected by arm or by sex. There were some main arm effects on EMG activity amplitude, with higher activity on the DA's pectoralis major (p < 0.001), and on the NDA's middle (p = 0.009) and posterior deltoid (p = 0.001) and infraspinatus (p < 0.001). The pectoralis major was affected by arm and fatigue mostly in males. Their DA's pectoralis major activity amplitude was higher, and the amplitude variability was lower, compared to the NDA, with both parameters showing fatigue-dependent decreases at the NDA only (arm x sex x fatigue: RMS: p = 0.007; SD: p = 0.001). As for females, the DA variability of their lower trapezius was smaller, and that of their subscapularis was higher, compared to the NDA (sex x arm, p = 0.028, p = 0.05). There was also more EMG variability on the supraspinatus' dominant side, and on the posterior deltoid and infraspinatus ND side. Results show an overhead shoulder flexion task dependency on pectoralis major control in males, and on lower trapezius and shoulder girdle stabilizers in females, which could be related to both sex- and gender-based factors. This knowledge can help identify side-specific injury risk factors due to overhead work in males and females, and help determine the appropriateness of implementing sex-specific workplace protocols, including alternating arms as fatigue compensatory and recovery strategies.

Occupation-Induced Fatigue and Impacts on Emergency First Responders: A Systematic Review

Fatigue in emergency first responders (EFRs) is known to affect performance abilities and safety outcomes for both patients and EFRs. The primary aim of this review was to determine the main contributors to occupation-induced fatigue in EFRs and its subsequent impacts. Following the PRIMSA checklist, academic databases (Medline, Embase, CINAHL, and SPORTDiscus) were searched using key terms with results subjected to inclusion and exclusion criteria. Populations of interest were firefighters, paramedics, or emergency call centre personnel. Of the 5633 records identified, 43 studies, which reported on 186 unique measures from a total population of 6373 participants, informed the review. Synthesis revealed fatigue was caused by lack of sleep during the shift and consistent poor sleep quality which negatively impacted cognitive function, alertness, and physical and mental health while increasing safety-compromising behaviours and injuries. Both subjective and objective assessments of fatigue are necessary for effective risk management in EFRs. EFRs that are consistently fatigued are at a greater risk of poor physical and mental health, reduced cognitive function, and increased injuries. No studies reported on fatigue in emergency call centre personnel, highlighting a literature gap. Funding was provided by the Australian Capital Territory Emergency Services Agency. Preregistration was filed in OSF: osf.io/26f3s.

Effectiveness of Functional or Aerobic Exercise Combined With Breathing Techniques in Telerehabilitation for Patients With Long COVID: A Randomized Controlled Trial

OBJECTIVE

The aim of this study was to compare the short-term clinical effects of 2 telerehabilitation programs, functional versus aerobic exercises (AEs), both combined with breathing techniques, regarding the improvement of long coronavirus disease 2019 (COVID-19) symptoms.

METHODS

A randomized controlled trial was conducted. The participants were assigned randomly to either the functional exercise (FE) group or AE group, both including breathing techniques. The interventions lasted for 8 weeks with 3 sessions per week, and they were conducted through the Fisiotrack mobile phone application. Assessments were performed at baseline and after treatment, including testing fatigue (Fatigue Assessment Scale), dyspnea (London Chest Activity of Daily Living Scale), functional performance (30 Seconds Standing Test), perceived stress (Perceived Stress Scale), anxiety and depression (Hospital Anxiety and Depression Questionnaire), and quality of life (European Quality of Life Scale). The perceived change after treatment (Patient Global Impression of Change Scale), the usability of the application (System Usability Scale), and the adherence to treatment were also examined after treatment.

RESULTS

In total, 43 participants (FE group, n = 21; AE group, n = 22; mean age = 42.4 [SD = 6.5] years) completed the study. In the intragroup comparison, the FE group showed improved fatigue (-6.7 points; 95% CI = -11.9 to -1.3), functional capacity (2.6 repetitions; 95% CI = 0.3 to 4.9), and perceived stress (-4.9 points; 95% CI = -9.1 to 0.8), while the AE group showed improved perceived stress (-6.2 points; 95% CI = -10.3 to -2.1). No significant differences in the intergroup effect were identified for the studied variables. Significant differences were observed in the Patient Global Impression of Change Scale in favor of the FE group compared to the AE group, and quality of life reached the minimal clinically important difference for both groups. The ease of use of the telerehabilitation tool was rated excellent in both groups.

CONCLUSIONS

Both telerehabilitation exercise modalities are effective at improving stress symptoms and quality of life in patients with long COVID-19. For improving fatigue and functional performance, FE shows more promising results.

IMPACT

FE or AE may be recommended depending on patients' symptoms, and both may improve quality of life and stress symptoms in patients with long COVID-19. Telerehabilitation may be an optimal intervention modality for the prescription of physical exercise in patients with long COVID-19.

A Comprehensive Evaluation of Multiple Sclerosis-Related Fatigue with a Special Focus on Fatigability

INTRODUCTION

Fatigue is the most common and disabling symptom in multiple sclerosis (MS), being reported by 55% to 78% of patients with MS (PwMS). Etiology of MS-related fatigue remains poorly understood, but an increased neuromuscular fatigability (i.e., greater loss of torque during exercise) could contribute to this phenomenon. This study aimed to characterize the correlates of MS-related fatigue in PwMS using a comprehensive group of physiological and psychosocial measures, with a particular focus on fatigability.

METHODS

Forty-two relapsing-remitting PwMS and 20 healthy subjects were recruited. PwMS were assigned in two groups (high (HF) and low (LF) fatigue) based on two fatigue questionnaires (Fatigue Severity Scale and Modified Fatigue Impact Scale). The main outcomes of this study are derived from incremental cycling completed to task failure (i.e., inability to pedal around 60 rpm). Maximal voluntary contraction (MVC), rating of perceived exertion, and central and peripheral parameters measured using transcranial magnetic and peripheral nerve stimulation were assessed in the knee extensor muscles before, during, and after the fatiguing task. Other potential correlates of fatigue were also tested.

RESULTS

MVC torque decreased to a greater extent for the HF group than LF group after the third common stage of the incremental fatiguing exercise (-15.7% ± 6.6% vs -5.9% ± 13.0%, P < 0.05), and this occurred concurrently with a higher rating of perceived exertion for HF (11.8 ± 2.5 vs 9.3 ± 2.6, P < 0.05). Subjective parameters (depression, quality of life) were worse for HF compared with LF and healthy subjects ( P < 0.001). Moreover, MVC torque loss at the final common stage and maximal heart rate explained 29% of the variance of the Modified Fatigue Impact Scale.

CONCLUSIONS

These results provide novel insight into the relationship between MS-related fatigue and fatigability among PwMS. The HF group exhibited greater performance fatigability, likely contributing to a higher perceived exertion than the LF group when measured during a dynamic task.

Investigating real-time physical activity behavior using ecological momentary assessment: Effects of mental fatigue and benefit-cost valuations

BACKGROUND

Current research investigating the relationship between mental fatigue and physical activity behaviors relies on laboratory-based, experimental studies which lack ecological validity.

OBJECTIVE

This study used ecological momentary assessment (EMA) to assess feelings of mental fatigue and subjective evaluations (benefits and costs) as predictors of moderate-to-vigorous intensity physical activity in the everyday lives of young adults.

METHODS

One hundred participants (n = 22 males, n = 78 females, Mage = 20.60 years, 70% meeting or exceeding physical activity guidelines) responded to digital survey prompts up to four times a day and wore an accelerometer for seven consecutive days. Moderate-to-vigorous intensity physical activity in the 180-min time window following each survey prompt was recorded. Data from the 28 survey-moderate-to-vigorous intensity physical activity epochs were analyzed using multilevel mixed-effects linear modelling.

RESULTS

Higher levels of mental fatigue than one's average level were associated with engaging in fewer moderate-to-vigorous intensity physical activity minutes (p = .004) and lower benefit vs. cost scores (p = .001). Higher benefit vs. cost scores than one's average level were associated with engaging in more minutes of moderate-to-vigorous intensity physical activity (p < .001).

CONCLUSIONS

Results are the first to demonstrate outside the lab, that mental fatigue experienced in everyday life may amplify the perceived costs of moderate-to-vigorous intensity physical activity, with both factors playing a potential role in moderate-to-vigorous intensity physical activity decision-making. Future research may apply insights gained from this study in design and testing of real-time interventions promoting moderate-to-vigorous intensity physical activity.

Ischemic Preconditioning, But Not Priming Exercise, Improves Exercise Performance in Trained Rock Climbers

ABSTRACT

MacDougall, KB, McClean, ZJ, MacIntosh, BR, Fletcher, JR, and Aboodarda, SJ. Ischemic preconditioning, but not priming exercise, improves exercise performance in trained rock climbers. J Strength Cond Res 37(11): 2149-2157, 2023-To assess the effects of ischemic preconditioning (IPC) and priming exercise on exercise tolerance and performance fatigability in a rock climbing-specific task, 12 rock climbers completed familiarization and baseline tests, and constant-load hangboarding tests (including 7 seconds on and 3 seconds off at an intensity estimated to be sustained for approximately 5 minutes) under 3 conditions: (a) standardized warm-up (CON), (b) IPC, or (c) a priming warm-up (PRIME). Neuromuscular responses were assessed using the interpolated twitch technique, including maximum isometric voluntary contraction (MVC) of the finger flexors and median nerve stimulation, at baseline and after the performance trial. Muscle oxygenation was measured continuously using near-infrared spectroscopy (NIRS) across exercise. Time to task failure (T lim ) for IPC (316.4 ± 83.1 seconds) was significantly greater than CON (263.6 ± 69.2 seconds) ( p = 0.028), whereas there was no difference between CON and PRIME (258.9 ± 101.8 seconds). At task failure, there were no differences in MVC, single twitch force, or voluntary activation across conditions; however, recovery of MVC and single twitch force after the performance trial was delayed for IPC and PRIME compared with CON ( p < 0.05). Despite differences in T lim , there were no differences in any of the NIRS variables assessed. Overall, despite exercise tolerance being improved by an average of 20.0% after IPC, there were no differences in neuromuscular responses at task failure, which is in line with the notion of a critical threshold of peripheral fatigue. These results indicate that IPC may be a promising precompetition strategy for rock climbers, although further research is warranted to elucidate its mechanism of action.

Electrically Evoked Isotonic Plantar Flexion Contractions Are Impaired Less than Voluntary After a Dynamic Fatiguing Task

PURPOSE

Evaluating central and peripheral processes responsible for reduced power after dynamic fatiguing tasks are often limited to isometric torque, which may not accurately reflect dynamic contractile performance. Here, we compare voluntary and electrically evoked peak power (and its determinants: dynamic torque and velocity) and rate of velocity development (RVD) before and after a dynamic fatiguing task using concentric Plantar flexion contractions.

METHODS

Young (18-32 yr) males ( n = 11) and females ( n = 2) performed maximal-effort isotonic Plantar flexion contractions using a load of 20% isometric torque until an approximately 75% reduction in peak power. Voluntary and electrically evoked (300 Hz tibial nerve stimulation) contractions loaded to 20% and 40% isometric torque through 25° ankle joint range of motion were compared before and 0, 2.5, 5, and 10 min after task termination.

RESULTS

At task termination, peak power and RVD of voluntary contractions at both loads were reduced more (~40% to 50% reduction) than electrically evoked (~25% to 35% reduction) contractions ( P < 0.001 and P = 0.003). Throughout the recovery period, electrically evoked peak power and RVD returned to baseline sooner (<5 min) than voluntary contractions, which were still depressed at 10 min. Reductions in peak power for the 20% load were equally due to impaired dynamic torque and velocity, whereas velocity was impaired more than dynamic torque ( P < 0.001) for the 40% load.

CONCLUSIONS

The relative preservation of electrically evoked power and RVD compared with voluntary contractions at task termination and quicker recovery to baseline indicates that the reductions in dynamic contractile performance after task termination are due to both central and peripheral processes; however, the relative contribution of dynamic torque and velocity is load dependent.

Analysis of Kinematic and Muscular Fatigue in Long-Distance Swimmers

Muscle fatigue is a complex phenomenon that is influenced by the type of activity performed and often manifests as a decline in motor performance (mechanical failure). The purpose of our study was to investigate the compensatory strategies used to mitigate mechanical failure. A cohort of 21 swimmers underwent a front-crawl swimming task, which required the consistent maintenance of a constant speed for the maximum duration. The evaluation included three phases: non-fatigue, pre-mechanical failure, and mechanical failure. We quantified key kinematic metrics, including velocity, distance travelled, stroke frequency, stroke length, and stroke index. In addition, electromyographic (EMG) metrics, including the Root-Mean-Square amplitude and Mean Frequency of the EMG power spectrum, were obtained for 12 muscles to examine the electrical manifestations of muscle fatigue. Between the first and second phases, the athletes covered a distance of 919.38 ± 147.29 m at an average speed of 1.57 ± 0.08 m/s with an average muscle fatigue level of 12%. Almost all evaluated muscles showed a significant increase (p < 0.001) in their EMG activity, except for the latissimus dorsi, which showed a 17% reduction (ES 0.906, p < 0.001) during the push phase of the stroke cycle. Kinematic parameters showed a 6% decrease in stroke length (ES 0.948, p < 0.001), which was counteracted by a 7% increase in stroke frequency (ES -0.931, p < 0.001). Notably, the stroke index also decreased by 6% (ES 0.965, p < 0.001). In the third phase, characterised by the loss of the ability to maintain the predetermined rhythm, both EMG and kinematic parameters showed reductions compared to the previous two phases. Swimmers employed common compensatory strategies for coping with fatigue; however, the ability to maintain a predetermined motor output proved to be limited at certain levels of fatigue and loss of swimming efficiency (Protocol ID: NCT06069440).

Cross-cultural adaptation and validation of vocal fatigue index (VFI) to Chinese language

Objectives: This study aimed to translate the Vocal Fatigue Index (VFI) into Simplified Chinese and test its reliability and validity in mainland China. Methods: The original English version of the VFI was translated and adapted to a Simplified Chinese version (VFI -SC). Fifty-four participants with voice disorders and 21 healthy controls completed the VFI-SC. Sixteen participants with voice disorders completed it again two weeks later. Reliability, validity, and receiver operating characteristic (ROC) of the VFI-SC were analyzed. Results: The Cronbach's alpha values for the VFI factor scores were found to be 0.930 for tiredness and avoidance of voice use (factor 1), 0.878 for physical discomfort with voice use (factor 2), and 0.915 for improvement of symptoms with voice rest (factor 3). The test-retest reliability was 0.967 for all three factors. There was a significant difference between the total scores of the patient group and the control group (p < 0.01). Factor 1 and factor 2 were positively correlated with the Voice Handicap Index (VHI-30). The ROC curves showed acceptable intrinsic accuracies for factor 1 (AUC = 0.883), factor 2 (AUC = 0.901), and factor 3 (AUC = 0.800), with cutoff scores of 22, 7, and 9, respectively. Conclusions: This study provides preliminary evidence that the VFI-SC has good reliability and validity. It can be used to screen for clinical symptoms of voice fatigue in mainland China.

Daily patterns of fatigue after subarachnoid haemorrhage: an ecological momentary assessment study

OBJECTIVE

To examine the daily course of, and factors associated with, momentary fatigue after subarachnoid haemorrhage, and to explore subgroups of patients with distinct diurnal patterns of fatigue.

DESIGN

Observational study using ecological momentary assessment.

SUBJECTS

A total of 41 participants with subarachnoid haemorrhage.

METHODS

Patients with fatigue were included within one year post-onset. Momentary fatigue (scale 1-7) was assessed with repeated measurements (10-11 times/day) during 7 consecutive days. Multilevel-mixed-model analyses and latent-class trajectory modelling were conducted.

RESULTS

Mean (standard deviation; SD) age of the group was 53.9 (13.0) years, 56% female, and mean (SD) time post-subarachnoid haemorrhage onset was 9.3 (3.2) months. Mean (SD) momentary fatigue over all days was 3.22 (1.47). Fatigue increased significantly (p < 0.001) over the day, and experiencing more burden of fatigue and day type (working day vs weekend day) were significantly (p < 0.05) associated with higher momentary fatigue. Three subgroups could be distinguished based on diurnal patterns of fatigue. The largest group (n = 17, 41.5%) showed an increasing daily pattern of fatigue.

CONCLUSION

Momentary fatigue in patients with subarachnoid haemorrhage increases over the day, and diurnal patterns of fatigue differ between  participants. In addition to conventional measures, momentary measures of fatigue might provide valuable information for physicians to optimize personalized management of fatigue after subarachnoid haemorrhage.

Changes in neuromuscular activation, heart rate and rate of perceived exertion over the course of a wheelchair propulsion fatigue protocol

Shoulder pain is common in persons with spinal cord injury and has been associated with wheelchair use. Fatigue related compensation strategies have been identified as possibly impacting the development of shoulder injury and pain. The purpose of this study was to investigate the progression of performance fatigability (i.e., decline in objective measure of performance including neuromuscular activation and increase in heart rate) and perceived fatigability (i.e., increased perceived exertion) during a 15-min fatigue protocol including maximum voluntary overground wheelchair propulsion. Fifty participants with paraplegic spinal cord injury completed three 4-min rounds of wheelchair propulsion, separated by 90 s of rest, on a figure-8 course consisting of two turns and full stops per lap in their manual wheelchairs (ClinicalTrials.gov: NCT03153033). Electromyography (EMG) signal of five muscles acting on the shoulder joint, heart rate (HR), and rate of perceived exertion (RPE) were measured at the beginning and end of every 4 min of propulsion. Root Mean Square (RMS) and Mean Power Frequency were calculated from EMG data. There was a significant increase in %RMS of the pectoralis major pars sternalis and trapezius pars descendens, HR, and RPE with greatest changes during the first 4 min of the protocol. The observed changes in neuromuscular activation in only two of the shoulder muscles may impact muscular imbalances and the development of shoulder injuries and should be further studied. The current study gives clearer insight into the mechanisms of performance fatigability and perceived fatigability throughout a wheelchair propulsion fatigue protocol.

Management of multiple sclerosis fatigue in the digital age: from assessment to treatment

Fatigue is one of the most disabling symptoms of Multiple Sclerosis (MS), affecting more than 80% of patients over the disease course. Nevertheless, it has a multi-faceted and complex nature, making its diagnosis, evaluation, and treatment extremely challenging in clinical practice. In the last years, digital supporting tools have emerged to support the care of people with MS. These include not only smartphone or table-based apps, but also wearable devices or novel techniques such as virtual reality. Furthermore, an additional effective and cost-efficient tool for the therapeutic management of people with fatigue is becoming increasingly available. Virtual reality and e-Health are viable and modern tools to both assess and treat fatigue, with a variety of applications and adaptability to patient needs and disability levels. Most importantly, they can be employed in the patient's home setting and can not only bridge clinic visits but also be complementary to the monitoring and treatment means for those MS patients who live far away from healthcare structures. In this narrative review, we discuss the current knowledge and future perspectives in the digital management of fatigue in MS. These may also serve as sources for research of novel digital biomarkers in the identification of disease activity and progression.

Electromyographic and mechanomyographic responses of the biceps brachii during concentric and eccentric muscle actions to failure at high and low relative loads

PURPOSE

This study examined neuromuscular responses of the biceps brachii (BB) for concentric and eccentric muscle actions during bilateral, dynamic constant external resistance (DCER), reciprocal forearm flexions and extensions to failure at high (80% 1 repetition maximum [1RM]) and low (30% 1RM) relative loads.

METHODS

Nine women completed 1RM testing and repetitions to failure (RTF) at 30 and 80% 1RM. Electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) signals were measured from the BB. Analyses included repeated measures ANOVAs (p < 0.05) and post-hoc pairwise comparisons with Bonferroni corrected alpha of p < 0.008 and p < 0.01 for between and within factor pairwise comparisons, respectively.

RESULTS

EMG AMP and MPF were significantly greater for concentric than eccentric muscle actions, regardless of load or time. However, time course of change analysis revealed parallel increases in EMG AMP for concentric and eccentric muscle actions during the RTF trials at 30% 1RM, but no change at 80% 1RM. There were significant increases in MMG AMP during concentric muscle actions, but decreases or no change during eccentric muscle actions. EMG and MMG MPF decreased over time, regardless of muscle action type and loading condition.

CONCLUSION

The greater EMG AMP and MPF values during concentric compared to eccentric muscle actions may reflect the difference in the efficiency characteristic of these muscle actions. The neuromuscular responses suggested that fatigue may be mediated by recruitment of additional motor units with lower firing rates during concentric muscle actions, and changes in motor unit synchronization during eccentric muscle actions.

Beyond the Lungs: O 2 Supplementation Improves Cerebral Oxygenation and Fatigue during Exercise in Interstitial Lung Disease

PURPOSE

Cerebral hypoxia may exacerbate the perception of fatigue. We previously demonstrated that exercise-related hypoxemia, a hallmark of fibrotic interstitial lung disease ( f -ILD), dose dependently impairs cerebral oxygenation in these patients. It is unknown whether normalizing cerebral oxygenation with O 2 supplementation would be associated with positive changes in a relevant patient-centered outcome during exercise in f -ILD, such as improved perceived fatigue.

METHODS

Fourteen patients (12 males, 72 ± 8 yr, 8 with idiopathic pulmonary fibrosis, lung diffusing capacity for carbon monoxide = 44% ± 13% predicted) performed a constant-load (60% peak work rate) cycle test to symptom limitation (Tlim) breathing medical air. Fourteen controls cycled up to Tlim of an age- and sex-matched patient. Patients repeated the test on supplemental O 2 (fraction of inspired O 2 = 0.41 ± 0.08) for the same duration. Near-infrared spectroscopy and the rating-of-fatigue (ROF) scale assessed prefrontal cortex oxygenation and perceived fatigue, respectively.

RESULTS

Patients showed severe exertional hypoxemia (Tlim O 2 saturation by pulse oximetry = 80% ± 8%); they had poorer cerebral oxygenation (e.g., oxy-deoxyhemoglobin difference [HbDiff] = -3.5 ± 4.7 [range = -17.6 to +1.9] vs +1.9 ± 1.7 μmol from rest) and greater fatigue (ROF = 6.2 ± 2.0 vs 2.6 ± 2.3) versus controls under air ( P < 0.001). Reversal of exertional hypoxemia with supplemental O 2 led to improved HbDiff (+1.7 ± 2.4 μmol from rest; no longer differing from controls) and lower ROF scores (3.7 ± 1.2, P < 0.001 vs air) in patients. There was a significant correlation between O 2 -induced changes in HbDiff and ROF scores throughout exercise in f -ILD ( rrepeated-measures correlation = -0.51, P < 0.001).

CONCLUSIONS

Supplemental O 2 improved cerebral oxygenation during exercise in f -ILD, which was moderately associated with lower ratings of perceived fatigue. Reversing cerebral hypoxia with O 2 supplementation may thus have positive effects on patients' disablement beyond those expected from lower ventilation and dyspnea in this patient population.

Intermittent blood flow occlusion modulates neuromuscular, perceptual, and cardiorespiratory determinants of exercise tolerance during cycling

PURPOSE

Constant blood flow occlusion (BFO) superimposed on aerobic exercise can impair muscle function and exercise tolerance; however, no study has investigated the effect of intermittent BFO on the associated responses. Fourteen participants (n = 7 females) were recruited to compare neuromuscular, perceptual, and cardiorespiratory responses to shorter (5:15s, occlusion-to-release) and longer (10:30s) BFO applied during cycling to task failure.

METHODS

In randomized order, participants cycled to task failure (task failure 1) at 70% of peak power output with (i) shorter BFO, (ii) longer BFO, and (iii) no BFO (Control). Upon task failure in the BFO conditions, BFO was removed, and participants continued cycling until a second task failure (task failure 2). Maximum voluntary isometric knee contractions (MVC) and femoral nerve stimuli were performed along with perceptual measures at baseline, task failure 1, and task failure 2. Cardiorespiratory measures were recorded continuously across the exercises.

RESULTS

Task failure 1 was longer in Control than 5:15s and 10:30s (P < 0.001), with no differences between the BFO conditions. At task failure 1, 10:30s elicited a greater decline in twitch force compared to 5:15s and Control (P < 0.001). At task failure 2, twitch force remained lower in 10:30s than Control (P = 0.002). Low-frequency fatigue developed to a greater extent in 10:30s compared to Control and 5:15s (P < 0.047). Dyspnea and Fatigue were greater for Control than 5:15s and 10:30s at the end of task failure 1 (P < 0.002).

CONCLUSION

Exercise tolerance during BFO is primarily dictated by the decline in muscle contractility and accelerated development of effort and pain.

Unraveling the interplay between daily life fatigue and physical activity after subarachnoid hemorrhage: an ecological momentary assessment and accelerometry study

BACKGROUND

Fatigue is one of the most commonly reported symptoms after subarachnoid hemorrhage (SAH) and is indirectly associated with physical activity (PA). Associations between fatigue and PA are primarily examined based on conventional measures (i.e. a single fatigue score or average PA levels), thereby assuming that fatigue and PA do not fluctuate over time. However, levels of fatigue and PA may not be stable and may interrelate dynamically in daily life. Insight in direct relationships between fatigue and PA in daily life, could add to the development of personalized rehabilitation strategies. Therefore we aimed to examine bidirectional relationships between momentary fatigue and PA in people with SAH.

METHODS

People (n = 38) with SAH who suffer from chronic fatigue were included in an observational study using Ecological Momentary Assessment (EMA) and accelerometry. Momentary fatigue was assessed on a scale from 1 to 7 (no to extreme fatigue), assessed with 10-11 prompts per day for 7 consecutive days using EMA with a mobile phone. PA was continuously measured during this 7-day period with a thigh-worn Activ8 accelerometer and expressed as total minutes of standing, walking, running and cycling in a period of 45 min before and after a momentary fatigue prompt. Multilevel mixed model analyses including random effects were conducted.

RESULTS

Mean age was 53.2 years (SD = 13.4), 58% female, and mean time post SAH onset was 9.5 months (SD = 2.1). Multilevel analyses with only time effects to predict fatigue and PA revealed that fatigue significantly (p < 0.001) increased over the day and PA significantly (p < 0.001) decreased. In addition, more PA was significantly associated with higher subsequent fatigue (β = 0.004, p < 0.05) and higher fatigue was significantly associated with less subsequent PA (β=-0.736, p < 0.05). Moreover, these associations significantly differed between participants (p < 0.001).

CONCLUSIONS

By combining EMA measures of fatigue with accelerometer-based PA we found that fatigue and PA are bidirectionally associated. In addition, these associations differ among participants. Given these different bidirectional associations, rehabilitation aimed at reducing fatigue should comprise personalized strategies to improve both fatigue and PA simultaneously, for example by combining exercise therapy with cognitive behavioral and/or energy management therapy.

Effectiveness of physical activity interventions on reducing perceived fatigue among adults with chronic conditions: a systematic review and meta-analysis of randomised controlled trials

Fatigue is barrier of physical activity participation in adults with chronic conditions. However, physical activity alleviates fatigue symptoms. This systematic review and meta-analysis aimed to (1) synthesise evidence from randomised controlled trials (RCTs) exploring the effects of physical activity interventions on fatigue reduction and (2) evaluate their effectiveness. Medline/CINAHL/EMBASE/Web of Science and Scopus were searched up to June 24th, 2023. Two reviewers independently conducted study screening and selection (RCTs), extracted data and assessed risk of bias (RoB2). Outcome was the standardised mean difference (SMD) with 95% confidence intervals in fatigue between experimental and control groups. 38 articles met the inclusion criteria. Overall, physical activity interventions moderately reduced fatigue (SMD = 0.54, p < 0.0001). Interventions lasting 2-6 weeks demonstrated a larger effect on fatigue reduction (SMD = 0.86, p < 0.00001). Interventions with 18-24 sessions showed a large effect on fatigue reduction (SMD = 0.97, p < 0.00001). Aerobic cycling and combination training interventions had a large to moderate effect (SMD = 0.66, p = 0.0005; SMD = 0.60, p = 0.0010, respectively). No long-term effects were found during follow-up. Physical activity interventions moderately reduced fatigue among adults with chronic conditions. Duration, total sessions, and mode of physical activity were identified as key factors in intervention effectiveness. Further research is needed to explore the impact of physical activity interventions on fatigue.

Effects of sleep deprivation on perceived and performance fatigability in females: An exploratory study

Sleep deprivation (SD) is prevalent and impairs motor function; however, little is known about its effect on perceived and performance fatigability, especially in females. To examine the effects of 24 h of SD on these attributes of fatigue, nine females completed a 20-min isometric, sustained elbow flexion contraction, followed by 10 min of recovery. The superimposed twitch (SIT) elicited via transcranial magnetic stimulation (TMS) assessed supraspinal drive. Biceps brachii electromyographic data indicated neural excitability in response to stimulation over the motor cortex (motor evoked potential; MEP), corticospinal tract (cervicomedullary motor evoked potential; CMEP), and brachial plexus (maximal M-wave; Mmax). MEPs and CMEPs were recorded during a TMS-induced silent period. At baseline, ratings of perceived effort (RPE; 2.9 vs. 1.6) and fatigue (RPF; 6.9 vs. 2.9), were higher for SD than control. Across the 20-min contraction, RPE increased from 2.2 to 7.6, SIT and MEP/CMEP increased by 284 and 474%, respectively, whereas maximal voluntary isometric contraction (MVC) torque and CMEP/Mmax decreased by 26 and 57%, respectively. No differences were found across conditions for MVC, SIT, Mmax, CMEP/Mmax, or MEP/CMEP prior to, during, and after the fatiguing task. During recovery, RPE (4.9 vs. 3.4), RPF (7.6 vs. 2.8), and perception of task difficulty (5.5 vs. 4.5) were greater for SD than control. Acute SD does not appear to alter performance fatigability development and subsequent recovery; however, it increases perceptions of fatigue, effort, and task difficulty. Thus, the disconnect between perceived and actual neuromuscular capacity following a sustained, submaximal isometric task is exacerbated by SD.HighlightsSleep deprivation did not alter supraspinal drive or neural excitability during and after a 20-min submaximal elbow flexion contractionSleep deprivation increased perceived fatigue and perception of task difficultyThe disconnect between perceived and performance fatigability is exacerbated in a sleep-deprived state.

Performance Fatigability and Neuromuscular Responses Are Not Joint Angle Specific Following a Sustained Isometric Forearm Flexion Task Anchored to a High Perceptual Intensity in Women

OBJECTIVES

To examine the effects of joint angle (JA) on maximal voluntary isometric contractions (MVIC) and neuromuscular responses following a sustained, isometric forearm flexion task anchored to a rating of perceived exertion (RPE) of 8 (RPE=8).

METHODS

Nine women (age: 20.7±2.9 yrs; height: 168.8±7.2 cm; body mass: 66.3±6.8 kg) performed 2,3s forearm flexion MVICs at JAs of 75°, 100°, and 125° prior to and following a sustained, isometric forearm flexion task anchored to RPE=8 to task failure (torque reduced to zero) at JA100. Electromyographic (EMG) and mechanomyographic (MMG) signals were recorded from the biceps brachii.

RESULTS

The MVIC at JA100 (collapsed across Time) was significantly greater (p<0.05) than JA75 and JA125. The pre-test MVIC was significantly greater (p<0.001) than the post-test. For EMG amplitude (AMP) and EMG mean power frequency (MPF), pre-test values were significantly greater (p<0.05) than the post-test values, with no differences between JAs. For MMG AMP and MMG MPF, there were no significant (p>0.05) differences between Time or JAs. Pre-test neuromuscular efficiency (normalized MVIC/normalized EMG AMP) was significantly greater (p=0.005) than post-test.

CONCLUSION

Following a sustained, isometric forearm flexion task anchored to RPE=8 at JA100, the fatigue-induced MVIC and neuromuscular responses were not affected by JA.

Individualised reference ranges for markers of muscle recovery assessment in soccer

Recently an individualisation algorithm has been developed and shown to significantly improve the diagnostic accuracy of creatine kinase (CK) and urea in endurance sports and Badminton. In this study, the applicability and benefit of this algorithm was evaluated using repeated measures data from 161 professional German soccer players monitored during the 2015-2017 seasons. Venous blood samples were collected after a day off (recovered state) and after a minimum of two strenuous training sessions within 48 h (non-recovered state) and analysed for CK and urea. Group-based reference ranges were derived from that same dataset to ensure the best possible reference for comparison. A z-test was conducted to analyse differences in error rates between individualised and group-based classifications. CK values for the individualised approach showed significantly lower error rates in the assessment of muscle recovery compared to both a population-based (p < .001; z-value: -17.01; test-pass error rate: 21 vs. 67%; test-fail: 19 vs. 64%) and a group-based cut-off (p < .001; z-value: -15.29; test-pass error rate: 65%; test-fail: 67%). It could be concluded that the assessment of muscle recovery in soccer using individualised interpretations of blood-borne markers may offer higher diagnostic accuracy than a population-based and a sample-specific group-based approach.HighlightsAssessing muscle recovery via CK using individualised ranges seems to offer a higher diagnostic accuracy than a sample-specific group-based analysis.Using an individualised algorithm seems to be a promising approach to overcome diagnostic problems arising from large inter- and intraindividual variability in blood parameters as it significantly improved the diagnostic accuracy of CK as a recovery marker.As recovery assessment in elite soccer ultimately aims at the accurate detection of differences in the individual player this algorithm seems to offer coaches and sport scientists a more sensitive approach compared to group-specific evaluations.

Blood Pressure Responses to Postexercise Circulatory Occlusion Are Attenuated After Exercise-Induced Muscle Weakness

PURPOSE

Exercise blood pressure (BP) responses are thought to be determined by relative exercise intensity (percent maximal voluntary contraction (MVC) strength). However, cross-sectional studies report that during a static contraction, higher absolute force is associated with greater BP responses to relative intensity exercise and subsequent muscle metaboreflex activation with postexercise circulatory occlusion (PECO). We hypothesized that a bout of unaccustomed eccentric exercise would reduce knee extensor MVC and subsequently attenuate BP responses to PECO.

METHODS

Continuous BP, heart rate, muscle oxygenation, and knee extensor electromyography were recorded in 21 young healthy individuals (female, n = 10) during 2 min of 20% MVC static knee extension exercise and 2 min of PECO, performed before and 24 h after 300 maximal knee extensor eccentric contractions to cause exercise-induced muscle weakness. As a control, 14 participants repeated the eccentric exercise 4 wks later to test whether BP responses were altered when exercise-induced muscle weakness was attenuated via the protective effects of the repeated bout effect.

RESULTS

Eccentric exercise reduced MVC in all participants (144 ± 43 vs 110 ± 34 N·m, P < 0.0001). BP responses to matched relative intensity static exercise (lower absolute force) were unchanged after eccentric exercise ( P > 0.99) but were attenuated during PECO (systolic BP: 18 ± 10 vs 12 ± 9 mm Hg, P = 0.02). Exercise-induced muscle weakness modulated the deoxygenated hemoglobin response to static exercise (64% ± 22% vs 46% ± 22%, P = 0.04). When repeated after 4 wks, exercise-induced weakness after eccentric exercise was attenuated (-21.6% ± 14.3% vs -9.3 ± 9.7, P = 0.0002) and BP responses to PECO were not different from control values (all, P > 0.96).

CONCLUSIONS

BP responses to muscle metaboreflex activation, but not exercise, are attenuated by exercise-induced muscle weakness, indicating a contribution of absolute exercise intensity on muscle metaboreflex activation.

The Effect of a Mental Task Versus Unilateral Physical Fatigue on Non-Local Muscle Fatigue in Recreationally Active Young Adults

Non-local muscle fatigue (NLMF) has been attributed to both physical and mental fatigue. The purpose of this study was to investigate the effects of mental exertion versus unilateral physical fatigue on NLMF. Sixteen recreationally active participants completed a physical task (2-sets of 100-s unilateral knee extension (KE) maximal voluntary isometric contractions (MVIC) with the dominant leg with 40-s recovery between sets, mental task (4-minute Stroop task), and control condition. Before and after each condition, blood lactate was collected, and contralateral 5-s KE, flexion (KF) and bilateral lateral trunk flexors MVIC (measure of trunk stability strength) was performed. Following the post-test 5-s MVICs, participants performed 12 non-dominant KE MVICs with a work-to-rest ratio of 5/10-s. Electromyography was monitored during the MVICs. Neither the 4-minute Stroop test or the unilateral KE physical fatigue intervention adversely affected the non-dominant KE forces or EMG activity with a single MVIC or 12 repetition MVICs. Although the non-dominant KF fatigue index forces and hamstrings EMG were not impaired by the interventions, there was a significant interaction (p = 0.001) small magnitude (d = 0.42) decrease in the non-dominant KF single MVIC force following the contralateral fatigue intervention, albeit with no significant change in hamstrings EMG. This MVIC deficit may be related to the significant decrease in dominant (p = 0.046, d = 2.6) and non-dominant external obliques (p = 0.048, d = 0.57) activation adversely affecting trunk stability. In conclusion, a 4-minute Stroop test or unilateral KE physical fatigue intervention did not impair non-dominant KE single or repeated 12 repetition MVIC forces or EMG activity. The small magnitude deficit in the non-dominant KF single MVIC force following the contralateral fatigue intervention are in accord with the heterogenous findings common in the literature.

Running Mechanics After Repeated Sprints in Femoroacetabular Impingement Syndrome, Cam Morphology, and Controls

BACKGROUND

People with femoroacetabular with femoroacetabular impingement syndrome (FAIS) often report pain during sports involving repeated sprinting. It remains unclear how sports participation influences running biomechanics in individuals with FAIS.

HYPOTHESIS

Changes in running biomechanics and/or isometric hip strength after repeated sprint exercise would be greatest in individuals with FAIS compared with asymptomatic individuals with (CAM) and without cam morphology (Control).

STUDY DESIGN

Controlled laboratory study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Three-dimensional hip biomechanics during maximal running (10 m) and hip strength were measured in 49 recreationally active individuals (FAIS = 15; CAM = 16; Control = 18) before and after repeated sprint exercise performed on a nonmotorized treadmill (8-16 × 30 m). Effects of group and time were assessed for biomechanics and strength variables with repeated-measures analyses of variance. Relationships between hip pain (Copenhagen Hip and Groin Outcome Score) and changes in hip moments and strength after repeated sprint exercise were determined using Spearman's correlation coefficients (ρ).

RESULTS

Running speed, hip flexion angles, hip flexion and extension moments, and hip strength in all muscle groups were significantly reduced from pre to post. No significant between-group differences were observed before or after repeated sprint exercise. No significant relationships (ρ = 0.04-0.30) were observed between hip pain and changes in hip moments or strength in the FAIS group.

CONCLUSION

Changes in running biomechanics and strength after repeated sprint exercise did not differ between participants with FAIS and asymptomatic participants with and without cam morphology. Self-reported pain did not appear to influence biomechanics during running or strength after repeated sprint exercise in participants with FAIS.

CLINICAL RELEVANCE

A short bout of repeated sprinting may not elicit changes in running biomechanics in FAIS beyond what occurs in those without symptoms. Longer duration activities or activities requiring greater hip flexion angles may better provoke pathology-related changes in running biomechanics in people with FAIS.

Fatiguing Joint Angle Does Not Influence Torque and Neuromuscular Responses Following Sustained, Isometric Forearm Flexion Tasks Anchored to Perceptual Intensity in Men

This study examined the effects of joint angle (JA) on maximal voluntary isometric contraction (MVIC) and neuromuscular responses following fatiguing tasks anchored to RPE. Nine men (mean ± SD: age = 20.7 ± 1.2 yrs) performed forearm flexion MVICs at elbow JAs of 75° and 125° before and after sustained, isometric forearm flexion tasks to failure at fatiguing joint angles (FJA) of 75° and 125° anchored to RPE = 8. The amplitude and frequency of the electromyographic and mechanomyographic signals were recorded. Neuromuscular efficiency was calculated by dividing normalized torque by normalized electromyographic amplitude. A dependent t-test was used to assess the mean difference for time to task failure (TTF) between FJA. Repeated measure ANOVAs were used to assess mean differences for pre-test to post-test MVIC and neuromuscular responses. There was no significant difference between FJA for TTF (p = 0.223). The MVIC (collapsed across FJA and MVIC JA) decreased from pre-test to post-test (51.1 ± 5.0 vs. 45.3 ± 5.6 Nm, p < 0.001). Normalized neuromuscular parameters remained unchanged (p > 0.05). The FJA resulted in similar torque and neuromuscular responses, and the decreases in MVIC were not tracked by changes in the neuromuscular parameters. Thus, the neuromuscular parameters were not sensitive to fatigue, and pre-test to post-test measures may be compared between different FJA.

Neuromuscular fatigue in autoimmune myasthenia gravis: A cross-sectional study

OBJECTIVES

To investigate the presence of increased neuromuscular fatigue (NMF) in individuals with myasthenia gravis (IwMG), compared to healthy controls. A secondary aim was to assess associations between NMF, strength and perceived health-related quality of life (HRQoL) and symptom severity in IwMG.

METHODS

In this cross-sectional study, we assessed NMF using classical myoelectrical indicators (root mean square: RMS, mean power frequency: MPF) obtained from surface electromyography (sEMG) during a sustained submaximal isometric contraction of the right Biceps Brachii and the right Vastus Lateralis and by evaluating the post-effort decline in peak torque following a fatiguing task consisting of a 40-second sustained isometric contraction. Relationships with MG-specific clinical scores (Myasthenia Muscle Score for symptom severity, MGQOL-15-F for HRQoL) were investigated.

RESULTS

Forty-one females with MG were compared to 18 control females of similar age. IwMG demonstrated reduced strength in both muscle groups, compared to control subjects. In both populations and both limbs, NMF was demonstrated by an increase in RMS and a decrease in MPF. However, IwMG did not demonstrate greater NMF based on these myoelectrical indicators nor based on post-effort peak torque decline.

DISCUSSION

Despite a decrease in baseline strength, IwMG did not display greater NMF in this specific experimental paradigm. This cohort consisted of individuals with mild-to-moderately severe MG which was well-controlled and stable. Further studies are warranted to identify simple and reliable methods to measure NMF in MG and to understand the relationship between NMF and perceived fatigue in activities of daily living for IwMG.

Reliability and sensitivity to change of post-match physical performance measures in elite youth soccer players

Introduction

To effectively monitor post-match changes in physical performance, valid, reliable and practical measures which are sensitive to change are required. This study aimed to quantify test-retest reliability and sensitivity to change of a range of physical performance measures recorded during an isometric posterior chain (IPC) lower-limb muscle test and a countermovement jump (CMJ) test.

Methods

Eighteen Italian Serie A academy soccer players performed three IPC repetitions per limb and five CMJ trials in 4 testing sessions. Test-retest reliability was evaluated between two testing sessions seven days apart using typical error of measurement, coefficient of variation and intraclass correlation coefficient. Sensitivity to change was assessed on two additional testing sessions performed before and immediately after a soccer match through Hedges' g effect size (g) and comparisons to typical error.

Results

Absolute reliability (coefficient of variations) ranged from 1.5 to 8.8%. IPC and CMJ measures demonstrated moderate to excellent relative reliability (intraclass correlation coefficients ranged from 0.70 to 0.98). A wide range of physical performance measures showed significant alterations post-match (p < 0.05; g: small to moderate). IPC peak force and torque, CMJ reactive strength index modified, CMJ eccentric forces (mean breaking force, mean deceleration force, peak force, force at zero velocity) and CMJ mean power measures had post-match changes greater than their typical variation, demonstrating acceptable sensitivity in detecting performance changes at post-match.

Discussion

IPC peak force and torque, CMJ reactive strength index modified, CMJ eccentric phase forces and CMJ mean power were found to be both reliable and sensitive to change, and thus may be appropriate for monitoring post-match neuromuscular performance in youth soccer population.

Effects of induced motor fatigue on walking mechanics and energetics

Lower-body robotic exoskeletons can be used to reduce the energy demand of locomotion and increase the endurance of wearers. Understanding how motor fatigue affects walking performance may lead to better exoskeleton designs to support the changing physical capacity of an individual due to motor fatigue. The purpose of this study was to investigate the effects of motor fatigue on walking mechanics and energetics. Treadmill walking with progressively increased incline gradient was used to induce motor fatigue. Twenty healthy young participants walked on an instrumented treadmill at 1.25 m/s and 0° of incline for 5 min before (PRE) and after (POST) motor fatigue. We examined lower-limb joint mechanics, metabolic cost, and the efficiency of positive mechanical work (η+work). Compared to PRE, participants had increased net metabolic power by ∼14% (p < 0.001) during POST. Participants also had increased total-limb positive mechanical power (Total P+mech) by ∼4% during POST (p < 0.001), resulting in a reduced η+work by ∼8% (p < 0.001). In addition, the positive mechanical work contribution of the lower-limb joints during POST was shifted from the ankle to the knee while the negative mechanical work contribution was shifted from the knee to the ankle (all p < 0.017). Although greater knee positive mechanical power was generated to compensate for the reduction in ankle positive power after motor fatigue, the disproportionate increase in metabolic cost resulted in a reduced walking efficiency. The findings of this study suggest that powering the ankle joint may help delay the onset of the lower-limb joint work redistribution observed during motor fatigue.

Taurine supplementation enhances anaerobic power in elite speed skaters: A double-blind, randomized, placebo-controlled, crossover study

Taurine (2-aminoethanesulfonic acid) is a semi-essential sulphur-containing amino acid abundant in skeletal muscle. Taurine supplementation is popular among athletes and has been purported to enhance exercise performance. This study aimed to investigate the ergogenic effects of taurine supplementation on anaerobic (Wingate; WanT) performance, blood lactate, ratings of perceived exertion (RPE), and countermovement vertical jump (CMJ) in elite athletes. For this study, randomized, double-blind, placebo-controlled crossover designs were used. Thirty young male speed skaters were randomly assigned to either taurine (TAU; single dose of 6 g) or placebo (PLAC; single dose of 6 g) 60 minutes before testing. Following a 72-hour washout, period participants completed the opposite condition. TAU improved peak (Δ% = 13.41, p < 0.001, d = 1.71), mean (Δ% = 3.95, p = 0.002, d = 1.04), and minimum power output (Δ% = 7.89, p = 0.034, d = 0.48) compared to placebo. Further, RPE (Δ% = -10.98, p = 0.002, d = 0.46) was significantly lower following the WanT in the TAU condition compared to placebo. There were no differences between conditions for the countermovement vertical jump. In conclusion, acute TAU supplementation augments anaerobic performance in elite speed skaters.

Molecular and biochemical investigations of the anti-fatigue effects of tea polyphenols and fruit extracts of Lycium ruthenicum Murr. on mice with exercise-induced fatigue

Background: The molecular mechanisms regulating the therapeutic effects of plant-based ingredients on the exercise-induced fatigue (EIF) remain unclear. The therapeutic effects of both tea polyphenols (TP) and fruit extracts of Lycium ruthenicum (LR) on mouse model of EIF were investigated. Methods: The variations in the fatigue-related biochemical factors, i.e., lactate dehydrogenase (LDH), superoxide dismutase (SOD), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-2 (IL-2), and interleukin-6 (IL-6), in mouse models of EIF treated with TP and LR were determined. The microRNAs involved in the therapeutic effects of TP and LR on the treatment of mice with EIF were identified using the next-generation sequencing technology. Results: Our results revealed that both TP and LR showed evident anti-inflammatory effect and reduced oxidative stress. In comparison with the control groups, the contents of LDH, TNF-α, IL-6, IL-1β, and IL-2 were significantly decreased and the contents of SOD were significantly increased in the experimental groups treated with either TP or LR. A total of 23 microRNAs (21 upregulated and 2 downregulated) identified for the first time by the high-throughput RNA sequencing were involved in the molecular response to EIF in mice treated with TP and LR. The regulatory functions of these microRNAs in the pathogenesis of EIF in mice were further explored based on Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses with a total of over 20,000-30,000 target genes annotated and 44 metabolic pathways enriched in the experimental groups based on GO and KEGG databases, respectively. Conclusion: Our study revealed the therapeutic effects of TP and LR and identified the microRNAs involved in the molecular mechanisms regulating the EIF in mice, providing strong experimental evidence to support further agricultural development of LR as well as the investigations and applications of TP and LR in the treatment of EIF in humans, including the professional athletes.

Unilaterally Induced Quadriceps Fatigue during Sustained Submaximal Isometric Exercise Does Not Alter Contralateral Leg Extensor Performance

This study investigated the effects of fatiguing unilateral exercise on the ipsilateral, exercised, and contralateral, non-exercised limb's post-exercise performance in males and females. Ten males and ten females performed a fatiguing, unilateral isometric leg extension at 50% maximal voluntary isometric contraction (MVIC) force. Prior to and immediately after the fatiguing tasks, MVICs were performed for the exercised and non-exercised limb, with surface electromyographic (sEMG) and mechanomyography (sMMG) amplitude (AMP) and mean power frequency (MPF) recorded from each limb's vastus lateralis. There were no fatigue-induced, sex-dependent, differences in time to task failure (p = 0.265) or ipsilateral performance fatigability (p = 0.437). However, there was a limb by time interaction (p < 0.001) which indicated decreases in MVIC force of the ipsilateral, exercised (p < 0.001), but not the contralateral, non-exercised limb (p = 0.962). There were no sex-dependent, fatigue-induced differences in neurophysiological outcomes between the limbs (p > 0.05), but there was a fatigue-induced difference in sEMG MPF (p = 0.005). To summarize, there were no differences in fatigability between males and females. Moreover, there was insufficient evidence to support the presence of a general crossover effect following submaximal unilateral isometric exercise. However, independent of sex, the neurophysiological outcomes suggested that competing inputs from the nervous system may influence the performance of both limbs following unilateral fatigue.

Recovery of pinch force sense after short-term fatigue

The aim of this study was to identify the exact origin of force sense and identify whether it arises centrally or peripherally. The present study was designed to analyze the effects of short-term fatigue on pinch force sense and the duration of these effects. During the fatigue protocol, twenty (10 men and 10 women; Mage = 22.0 years old) young Chinese participants were asked to squeeze maximally until the pinch grip force decreased to 50% of its maximal due to fatigue. Participants were instructed to produce the target force (10% of maximal voluntary isometric contraction) using the same hand before and after fatigue (immediately, 10, 30, 60, 180, 300 s). The results showed significantly higher absolute error immediately after fatigue (1.22 ± 1.06 N) than before fatigue (0.68 ± 0.34 N), and 60 s (0.76 ± 0.69 N), 180 s (0.67 ± 0.42 N), and 300 s (0.75 ± 0.37 N) after fatigue (all P < 0.05) but with no effect on the variable error (P > 0.05). It was also revealed that there was a significant overestimate of the constant error values before (0.32 ± 0.61 N) and immediately after fatigue (0.80 ± 1.38 N, all P < 0.05), while no significant overestimation or underestimation exceeded 300 s after fatigue (P > 0.05). Our study results revealed that short-term fatigue resulted in a significant decrease in force sense accuracy, but it did not affect force sense consistently; however, force sense accuracy recovered to a certain extent within 10 s and 30 s, whereas it recovered fully within 60 s, and force sense directivity improvement exceeded 300 s after fatigue. The present study shows that the sense of tension (peripherally) is also an important factor affecting force sense. Our study supports the view that the periphery is part of the origin of force sense.

Influence of Exogenous Factors Related to Nutritional and Hydration Strategies and Environmental Conditions on Fatigue in Endurance Sports: A Systematic Review with Meta-Analysis

The aim of this systematic review with meta-analysis was to examine the influence of exogenous factors related to nutritional and hydration strategies and environmental conditions, as modulators of fatigue, including factors associated with performance fatigability and perceived fatigability, in endurance tests lasting 45 min to 3 h. A search was carried out using four databases: PubMed, Web of Science, SPORTDiscus, and EBSCO. A total of 5103 articles were screened, with 34 included in the meta-analysis. The review was registered with PROSPERO (CRD42022327203) and adhered to the PRISMA guidelines. The study quality was evaluated according to the PEDro score and assessed using Rosenthal's fail-safe N. Carbohydrate (CHO) intake increased the time to exhaustion (p < 0.001) and decreased the heart rate (HR) during the test (p = 0.018). Carbohydrate with protein intake (CHO + PROT) increased lactate during the test (p = 0.039). With respect to hydration, dehydrated individuals showed a higher rate of perceived exertion (RPE) (p = 0.016) and had a higher body mass loss (p = 0.018). In hot conditions, athletes showed significant increases in RPE (p < 0.001), HR (p < 0.001), and skin temperature (p = 0.002), and a decrease in the temperature gradient (p < 0.001) after the test. No differences were found when athletes were subjected to altitude or cold conditions. In conclusion, the results revealed that exogenous factors, such as nutritional and hydration strategies, as well as environmental conditions, affected fatigue in endurance sports, including factors associated with performance fatigability and perceived fatigability.

The Minimal Difference as an Individual Threshold to Examine the Utility of a Verification Bout in Determining V̇O 2max

PURPOSE

A square-wave verification bout to confirm maximal oxygen uptake (V̇O 2max ) from a graded exercise test (GXT) has been recommended based on mean responses. This study used the test-retest reliability, mean, and individual differences between the highest V̇O 2 from the GXT (V̇O 2GXT ) and verification bout (V̇O 2verification ) to examine the efficacy of a verification bout in the determination of O 2max in healthy, recreationally trained, well-motivated men.

METHODS

Ten men (24 ± 4 yr) completed a GXT on a cycle ergometer followed by a submaximal verification bout to determine V̇O 2GXT and V̇O 2verification . After completion of the initial GXT, subjects rested for 5 min then performed the verification bout at 90% of the peak power output from the initial GXT. Analyses included a two-way repeated-measures ANOVA, intraclass correlation coefficients (ICC 2,1 ), standard errors of the measurement (SEM), minimal differences (MD), and coefficients of variation (COV).

RESULTS

There was no test (test 1 vs test 2)-method (GXT vs verification) interaction ( P = 0.300) and no main effect for test ( P = 0.690), but there was a main effect for method ( P = 0.003). The V̇O 2GXT (46.0 mL⋅kg -1 ⋅min -1 ) was significantly greater than V̇O 2verification (43.9 mL⋅kg -1 ⋅min -1 ), collapsed across test. The V̇O 2GXT (ICC = 0.970, SEM = 1.63 mL⋅kg -1 ⋅min -1 , MD = 4.51 mL⋅kg -1 ⋅min -1 , COV = 3.54%) and the V̇O 2verification (ICC = 0.953, SEM = 1.87 mL⋅kg -1 ⋅min -1 , MD = 5.17 mL⋅kg -1 ⋅min -1 , COV = 4.25%) demonstrated "excellent" reliability. No subject exceeded the MD test-retest for V̇O 2GXT or V̇O 2verification . No subject had a V̇O 2verification that exceeded V̇O 2GXT by more than the MD, but two subjects had a V̇O 2GXT , which exceeded V̇O 2verification by more than the MD.

CONCLUSIONS

The excellent reliability of V̇O 2GXT in addition to the examination of the individual differences between V̇O 2GXT and V̇O 2verification using the MD indicated that a standalone GXT was sufficient to determine V̇O 2max .