Muscle fatigue: general understanding and treatment

Effect of dry needling on quadriceps muscles fatigue in taekwondo players: A protocol for a triple-blinded randomized controlled trial

Background

A common issue among athletes is muscle fatigue, a brief and transient reduction in the potential of skeletal muscle strength after engaging in muscular activity. A high-quality clinical investigation to evaluate the impact of dry needling (DN) on athletes' muscle fatigue is lacking. Therefore, this study aims to examine the effect of DN on quadriceps muscle fatigue in taekwondo players.

Methods

A triple-blind, randomized, controlled trial will be conducted to measure changes in quadriceps muscle fatigue after DN. Eighty-eight taekwondo players who meet the eligibility criteria will be selected to receive either DN or sham needling to the quadriceps muscle after exercise. Three assessments will be performed before the exercise, after exercise fatigue, and after intervention. The outcomes measured will be isometric peak torque, single-leg hop test, and vertical jump test.

Conclusions

The results of this study will provide preliminary evidence regarding the effectiveness of DN in improving quadriceps muscle fatigue in taekwondo players.

Trial registration

IRCT20210811052141N1.

Effects of kilohertz versus low-frequency electrical stimulation of the wrist extensors in patients after stroke: A randomized crossover trial

BACKGROUND

Electrical stimulation is an effective treatment method for improving motor function after stroke, but the optimal current type for patients with stroke and arm paresis remains unclear.

OBJECTIVE

To compare the effects of kilohertz frequency with low-frequency current on stimulation efficiency, electrically induced force, discomfort, and muscle fatigue in patients with stroke.

DESIGN

A randomized crossover study.

SETTING

Neurological inpatient rehabilitation clinic in Germany.

PARTICIPANTS

A total of 23 patients with arm paresis after stroke within the last 6 months were recruited, 21 were enrolled, and 20 completed the study (7 females; mean ± SD: 66 ± 12 years; 176 ± 11 cm; 90 ± 19 kg; 57 ± 34 days since stroke).

INTERVENTION

All patients underwent both kilohertz and low-frequency stimulation in a randomized order on 2 days (48-hour washout). Each day included a step protocol with a gradual increase in stimulation intensity, starting at the first measurable force (up to 12 steps, 1 mA increments, 8 seconds stimulation, 60 second rest) and a fatigue protocol (30 repetitions, 8 second stimulation, 3 second rest).

MAIN OUTCOME MEASURE

Primary outcome was stimulation efficiency (electrically induced force/stimulation intensity) [N/mA], measured during each step of the stepwise increase in current intensity protocol.

RESULTS

Linear-mixed-effects models showed significantly higher stimulation efficiency for low-frequency stimulation (mean difference 0.14 [95% confidence interval, 0.01-0.27 N/mA], p = .031). However, current type did not significantly affect electrically induced force, level of discomfort, or muscle fatigue (p > .05).

CONCLUSION

The findings suggest that low-frequency stimulation is more efficient than kilohertz-frequency stimulation. However, both current types yield similar effects on force, discomfort, and fatigue, making them both viable options for wrist extensor stimulation in patients after stroke. Considering the variability among individuals, customizing the current type based on electrically induced force and perceived discomfort may enhance therapeutic outcomes. Further research on the long-term treatment effects of both current types is warranted.

Does work posture affect static postural stability?

Fatigue that occurs following non-ergonomic work postures is a major reason for occupational falls. This study aimed to investigate the effects of four work postures (bending, squatting, sitting, and standing) on static postural stability. Twenty volunteers were recruited, and their static balance was assessed before (PRE), immediately after (POST 1), and after 10 minutes of resting (POST 2) following a simulation task in the four work postures until fatigue. Each postural sway variable in the four work postures during PRE, POST 1, and POST 2 was analysed using a one-way Analysis of Variance (ANOVA). Additionally, each postural sway variable in four work postures at POST 1 and POST 2 was analysed using one-way ANOVA. Results demonstrated poor static stability immediately after fatigue, especially in the sitting position. The findings of this study may aid in providing suggestions for re-designing certain work tasks to prevent falls and fall-related injuries.

Exercise-induced changes in high-γ cortical functional connectivity and short-interval intracortical inhibition

OBJECTIVE

To analyze exercise-induced changes in functional connectivity (FC) using high-density EEG (HD-EEG) and primary motor cortex excitability via paired-pulse TMS (pp-TMS).

METHODS

Ten healthy volunteers performed a 3 km high-intensity run. Neurophysiological assessments were conducted at baseline (T0), 24 h (T1), and 72 h (T2) post-exercise. FC was measured using HD-EEG, and primary motor cortex excitability was assessed with pp-TMS to measure short-interval intracortical inhibition (SICI) and facilitation (ICF).

RESULTS

At T1, a significant hyperconnected network in the high-γ band was observed in several brain regions, including sensorimotor, limbic, temporal, and occipital lobes, which normalized by T2. Additionally, pp-TMS revealed disinhibition (reduced SICI) in M1 at ISI 2-3 ms at T1.

CONCLUSIONS

The study highlighted specific features of exercise-induced central fatigue. Post-exercise, the primary motor cortex became hyperexcitable, possibly as a compensatory response to peripheral fatigue. A complex network of cortical areas involved in cognition and behavior was hyperactivated, likely reflecting awareness of fatigue and self-protection decision-making processes. These changes were reversible, allowing subjects to return to baseline conditions.

SIGNIFICANCE

This research provides insight into the neurophysiological mechanisms of central fatigue, emphasizing the brain's adaptive responses to intense physical activity and their temporal dynamics.

Improving dynamic endurance time predictions for shoulder fatigue: A comparative evaluation

Work-related musculoskeletal disorders (WMSDs) are commonplace in industry and a host of qualitative and quantitative approaches have been used to assuage the problem, including wearable sensors and biomechanical endurance models, both of which were used in the present study. Six endurance models (consumed endurance, new improved consumed endurance and the exponential and power Frey Law and Avin general and shoulder models) with four alternative maximum torque (Torquemax) quantification methods, including a novel approach to generate Torquemax, were compared. The proposed approach to quantify Torquemax, in combination with the new improved consumed endurance model produced the lowest root mean square errors (RMSE), and indicated improved performance compared to the literature. The mean RMSE was reduced from 41.08s to 19.11s for all subjects, from 26.13s to 12.16s for males, and 51.28s to 24.45s for females using the proposed method. R2 for 25% and 45% standardised intensity dynamic tasks were .459 and .314 respectively, P < .01. This research provided an optimised and individualised endurance prediction approach for loaded dynamic movements which can be applied to industry tasks and may lead to reduced upper-limb strains, and potentially WMSDs.

Plant polysaccharides and antioxidant benefits for exercise performance and gut health: from molecular pathways to clinic

In the last three decades, our understanding of how exercise induces oxidative stress has significantly advanced. Plant polysaccharides, such as dietary fibers and resistant starches, have been shown to enhance exercise performance by improving energy metabolism, reducing fatigue, increasing strength and stamina, mitigating oxidative stress post-exercise, facilitating muscle recovery, and aiding in detoxification. Moreover, antioxidants found in plant-based foods play a crucial role in protecting the body against oxidative stress induced by intense physical activity. By scavenging free radicals and reducing oxidative damage, antioxidants can improve exercise endurance, enhance recovery, and support immune function. Furthermore, the interaction between plant polysaccharides and antioxidants in the gut microbiota can lead to synergistic effects on overall health and performance. This review provides a comprehensive overview of the current research on plant polysaccharides and antioxidants in relation to exercise performance and gut health.

Measurement of Twitch Dynamics in Response to Exercise Induced Changes in Mitochondrial Disease Using Motor Unit Magnetic Resonance Imaging (MUMRI): A Proof-of-Concept Study

Muscle twitch dynamics and fatigability change in response to muscle disease. In this study, we developed an imaging paradigm to measure muscle twitch dynamics, and the response of the muscle to voluntary fatiguing contractions. We used a novel imaging technique called motor unit magnetic resonance imaging (MUMRI). MUMRI allows visualisation of muscle and motor unit activity by combining in-scanner electrical stimulation with dynamic pulsed gradient spin echo (twitch dynamics, PGSE-MUMRI) and phase contrast (fatigue, PC-MUMRI) imaging. In Part I of this study, we scanned 10 healthy controls, we measured the muscle rise (Trise), contraction (Tcontract) and half-relaxation time (Thalf-relax) of the tibialis anterior (TA) muscle on a voxel-wise basis using PGSE-MUMRI. Five controls were scanned twice to assess reproducibility; PGSE-MUMRI demonstrated reproducible results, with low variation between scans 3.4% for Trise, 6.4% for Tcontract and 7.1% for Thalf-relax. We then developed a PC-MUMRI paradigm to measure the recovery of the TA in response to a fatiguing voluntary exercise. In Part II of the study, we applied these two novel imaging paradigms in a cohort study of nine patients with single large-scale mtDNA deletion primary mitochondrial myopathy (PMM). Patients underwent a 12-week resistance exercise programme and baseline, and follow-up MRI was performed. PGSE-MUMRI detected a significantly longer muscle contraction time between baseline and follow-up in PMM patients 108.7 ± 7.9 vs. post-119.3 ± 10.4 ms; p = 0.018. There was no statistical difference in the recovery half maximum measured using PC-MUMRI in PMM patients between baseline and follow-up 254 ± 109 vs. 137 ± 41 s; p = 0.074. In conclusion, PGSE-MUMRI has detected differences in muscle twitch dynamics between controls and PMM following an exercise programme, and we can visualise differences in twitch dynamics subregions of muscle using this technique. The PC-MUMRI technique has shown promise as a novel measure of muscle fatigue.

Hybrid hydrolysates of soy protein and lactoferrin exerts synergistic antioxidant and anti-fatigue effect by modulating Keap1/Nrf2/HO-1 pathways

Oxidative stress is an important cause of exercise fatigue formation. Nutritional intervention is an important way to modulate exercise fatigue. Lactoferrin (LF) and soybean protein (SP) are potential antioxidant bioactive components. Our findings demonstrate that SP-LF hybrid hydrolysates had effective 2,2-diphenylpicrylhydrazyl (DPPH) and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radical scavenging activity and iron ion reducing ability. The synergistic effect between these hybrid hydrolysates were found to be superior to the single hydrolysate in terms of antioxidant level by the joint index analysis. These hybrid hydrolysates are characterized by high levels of amino acids with potential anti-fatigue effect: tyrosine (Tyr), phenylalanine (Phe), hydrophobic amino acid (HAAs) and branched-chain amino acids (BCAAs). In murine models, hybrid hydrolysates significantly prolonged weight-bearing swimming time, increased muscle/liver glycogen levels, decreased lactate, urea nitrogen, and malondialdehyde levels, and increased glutathione peroxidase, superoxide dismutase, catalase and ATPase activities. Pearson's correlation analysis established significant associations between antioxidant capacity and anti-fatigue efficacy. It alleviated fatigue through activating the Keap1/Nrf2/HO-1 signaling pathway, while increasing the expression levels of PGC-1α. These results collectively suggest that SP-LF hybrid hydrolysates demonstrate significant synergistic antioxidant and anti-fatigue activity and could be incorporated into functional foods as a dietary supplement to reduce fatigue.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

APOE- ε4 Modulates Facial Neuromuscular Activity in Nondemented Adults: Toward Sensitive Speech-Based Diagnostics for Alzheimer's Disease

The APOE-ε4 allele is a genetic risk factor for late-onset Alzheimer's disease (AD). Beyond cognitive decline, APOE-ε4 affects motor function, reducing muscle strength and coordination, potentially through mitochondrial dysfunction and oxidative stress. This study examined the influence of the APOE- ε4 allele on neuromuscular function in oral muscles involved in speech production, using surface electromyography (EMG); and assessed the predictive power of EMG measures in differentiating APOE- ε4 carriers from noncarriers. Forty-two cognitively intact adults (16 APOE- ε4 carriers, 26 noncarriers) completed speech tasks while EMG was recorded from seven craniofacial muscles. Seventy EMG features including amplitude, frequency, complexity, regularity, and functional connectivity were extracted. Statistical analyses assessed genotype effects, sex differences, and correlations with blood metabolic biomarkers. APOE- ε4 carriers exhibited increased motor unit recruitment and synchronization, suggesting accelerated muscle fatigue. EMG-based measures outperformed cognitive tests in distinguishing carriers (AUC = 0.90) and correlated with metabolic biomarkers. Sex differences emerged, with female carriers showing reduced and male carriers showing increased functional connectivity. These findings highlight speech-based neuromuscular changes as potential early biomarkers of Alzheimer's risk before cognition is affected.

Reference values for arm ergometry cardiopulmonary exercise testing (CPET) in healthy volunteers

INTRODUCTION

The performance of a cardiopulmonary exercise test (CPET) requires an individual to undertake a progressive, maximal exercise test to a symptom-limited end point. CPET is commonly performed using a treadmill or cycle ergometer (CE). Arm ergometry (AE) is an alternative exercise modality to CE; however, AE produces lower peak oxygen uptake (V̇O2) values as it involves smaller muscle groups and generates less cardiovascular stress. Current predicted equations for the interpretation of AE CPET are limited by small sample sizes, gender bias and limited age ranges.

AIMS

To develop predicted equations and reference ranges for AE exercise testing.

DESIGN

Incremental ramp protocol CPET, to a symptom-limited end point, via AE was performed in a group of 116 (62 F) healthy volunteers of median age 38 (IQR 29-48) years. Breath-by-breath gas analysis was performed using the Ultima CPX (Medical Graphics, UK) metabolic cart. Quantile regression analysis was used to develop regression equations for AE V̇O2, peak work rate (WR), anaerobic threshold, peak ventilation (VE), peak heart rate, oxygen pulse, V̇E/V̇CO2 slope and V̇O2/WR slope.

RESULTS

Reference equations including upper and/or lower limits, based on quantile regression, were generated and verified using a validation cohort.

CONCLUSIONS

These findings represent the largest and most diverse set of predicted values and reference ranges for AE CPET parameters in healthy individuals to date. Implementation of these reference equations will allow AE to be more widely adopted, enabling the performance and interpretation of CPET in a wider population.

Polyphenols and post-exercise muscle damage: a comprehensive review of literature

Recent research highlights the significant role of polyphenols in alleviating post-exercise muscle damage, thus positioning them as a valuable nutritional strategy for athletes and fitness enthusiasts. Polyphenols, naturally occurring bioactive compounds abundant in fruits, vegetables, tea, wine, and other plant-based foods, are recognized for their potent antioxidant and anti-inflammatory properties. This dual mechanism is critical for combating oxidative stress and inflammation-two factors that intensify during vigorous physical activity and contribute to muscle soreness and damage. Among various polyphenols, compounds like quercetin have particularly emerged as effective agents for promoting muscle recovery and enhancing exercise performance. These protective effects are facilitated through several mechanisms, including the modulation of inflammatory pathways, acceleration of muscle repair processes, and enhancement of mitochondrial function, all of which bolster overall muscle health. As ongoing studies yield deeper insights, the potential of polyphenols to enhance athletic performance and overall health will become increasingly substantiated, leading towards their strategic incorporation into exercise nutrition protocols. Therefore, we reviewed relevant studies in order to show how efficient polyphenols can be in reducing muscle fatigue and damage and what are the exact mechanisms.

Artificial intelligence applications in smile design dentistry: A scoping review

PURPOSE

Artificial intelligence (AI) applications are growing in smile design and aesthetic procedures. The current expansion and performance of AI models in digital smile design applications have not yet been systematically documented and analyzed. The purpose of this review was to assess the performance of AI models in smile design, assess the criteria of points of reference using AI analysis, and assess different AI software performance.

METHODS

An electronic review was completed in five databases: MEDLINE/PubMed, EMBASE, World of Science, Cochrane, and Scopus. Studies that developed AI models for smile design were included. The search strategy included articles published until November 1, 2024. Two investigators independently evaluated the quality of the studies by applying the Joanna Briggs Institute (JBI) Critical Appraisal Checklist for Quasi-Experimental Studies and Textual Evidence: Expert Opinion Results.

RESULTS

The search resulted in 2653 articles. A total of 2649 were excluded according to the exclusion criteria after reading the title, abstract, and/or full-text review. Four articles published between 2023 and 2024 were included in the present investigation. Two articles compared 2D and 3D points while one article compared the outcome of satisfaction between dentists and patients, and the last article emphasized the ethical components of using AI.

CONCLUSION

The results of the studies reviewed in this paper suggest that AI-generated smile designs are not significantly different from manually created designs in terms of esthetic perception. 3D designs are more accurate than 2D designs and offer more advantages. More articles are needed in the field of AI and smile design.

Twenty years of research on exercise-induced fatigue: A bibliometric analysis of hotspots, bursts, and research trends

Data from the Web of Science Core Collection (2004-2023) on "exercise-induced fatigue" were analyzed using bibliometric tools to explore research trends across countries, institutions, authors, journals, and keywords. The analysis was limited to "Article" and "Review" literature types. Among 4531 publications, the United States contributed the most articles (1005), followed by England (559) and China (516). The most influential institution was Universidade de São Paulo, while the most productive was Institut National de la Santé et de la Recherche Médicale with 103 papers. The European Journal of Applied Physiology ranked as the top journal with 233 articles. Millet Guillaume Y. emerged as the most prolific author, and Amann Markus was the most cited. Recent keyword trends showed a surge in terms like "physical activity" and "aerobic exercise," while "fatigue" and "exercise" remained dominant. Notable findings were observed in oncology, engineering, and multidisciplinary studies, indicating potential research trends. Oxidative stress was identified as the most commonly mentioned mechanism in exercise-induced fatigue studies. This bibliometric analysis highlights current research trends and gaps, suggesting that future studies should focus on understanding the mechanisms of exercise-induced fatigue, developing objective measurement criteria, and exploring strategies for its alleviation.

Preliminary investigation of anti-fatigue effects and potential mechanisms of meiju oral liquid in mouse and zebrafish models

Meiju Oral Liquid (MOL), a representative medicinal formula in China, stems from the traditional use of specific Chinese medicinal herbs known for their anti-fatigue properties, including rose, jujube, chicory, and wolfberry. While these individual herbs have been recognized for their benefits, the formulation of MOL itself has not been extensively studied. This study was designed to evaluate the potential anti-fatigue effects of MOL, prepared from these natural herbs, and to explore its underlying mechanisms. In this research, both mouse and zebrafish models were utilized to investigate the anti-fatigue effects of MOL. Chemical characterization of MOL and identification of bioactive compounds in serum were conducted using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). The results demonstrated that MOL significantly prolonged the weight-bearing swimming time in mice, increased hepatic and muscle glycogen content, and reduced serum levels of blood urea nitrogen, blood lactate, and inflammatory markers (IL-1β, IL-6, TNF-α, and NO). Furthermore, MOL down-regulated the expression of NOX4 and TNF-α proteins while up-regulating p-PI3K and p-AKT proteins in the liver tissues of fatigued mice. In zebrafish models, MOL exhibited protective effects against sodium sulfite-induced lethality, enhanced high-speed motion trajectories, and increased movement distances in both normal and fatigued zebrafish. Additionally, MOL downregulated IL-1β, IL-6, TNF-α, and TNF-β mRNA levels while up-regulating PI3K and AKT1 mRNA levels in fatigued zebrafish. These findings suggested that the anti-fatigue effects of MOL may be mediated through the activation of the PI3K/AKT signaling pathway as well as the inhibition of TNF-α and NOX4 expression. In addition, a total of ninety-four chemical components were identified in MOL, with twenty-three migration compounds detected in mouse serum. These migration compounds are likely the primary active agents, contributing to the reduction of metabolite accumulation, enhancement of glycogen synthesis, and suppression of inflammatory responses. Taken together, our findings underscore the potential anti-fatigue effects of MOL, warranting further investigation into its therapeutic applications and the specific roles of its bioactive compounds.

The contemporary role of lactate in exercise physiology and exercise prescription - a review of the literature

Lactate is a key molecule in exercise metabolism. In the last two decades, there has been a revolution in the understanding of its role - from a byproduct of hypoxic muscles to a major energy resource and a signaling molecule - 'lactormone'. The aim of this review is to compile all the up-to-date information that is available on the general metabolism of lactate, but also the specific use that exercise physiologists, coaches, and athletes can get out of lactate measurements, lactate-based training zones, and periodization of training sessions. Since the revolution in the understanding of lactate's role in normal metabolism and disease in the late 20th century, more evidence has been assembled regarding the specific part it plays in exercise. From the vast body of knowledge, the researchers developed the concept of training intensity distribution into zones according to the level of blood lactate. The end goal of training to a specific lactate level or 'threshold' is the increased adaptation to specific training stimuli and ultimately better performance, which has been backed up by the achievements of numerous athletes training according to this concept.

Changes in Physical Performance Following Operational Military Training: A Meta-Analysis

BACKGROUND

To best simulate armed combat-related emergencies, military personnel undergo operational training that attempts to recreate multiple physical stressors. Understanding the specific aspects of physical performance degradation after operational training helps to better inform future training practices, as these declines translate to real-world operations. The purpose of this meta-analysis was to investigate the effects of operational trainings on physical performance metrics in military personnel.

METHODS

Six electronic databases were searched for studies that investigated physical performance metrics in active-duty military personnel before and after multiple-day operational training. Sample sizes, means and standard deviations were extracted from included studies, and random-effects meta-analyses were conducted using standardized mean differences (Hedge's g) with 95% confidence intervals (p ≤ 0.05).

RESULTS

Seventeen studies (N = 1592 participants) were included for final review and grouped by physical performance metric. Meta-analyses revealed a large pre-to-post decline in lower body jump power (n = 4, g = 0.87, 95% CI [0.28, 1.47]), and small declines in short-duration lower body power-jump distance (n = 5, g = 0.39, 95% CI [0.16, 0.63]), upper body endurance (n = 4, g = 0.40, 95% CI [0.09, 0.71]), and core endurance (n = 2, g = 0.46, 95% CI [0.10, 0.82]). Substantial heterogeneity was observed in the included studies (I2 = 0-91%).

CONCLUSIONS

Military operational training temporarily diminishes lower body performance to a greater extent than other constructs. The most consistent findings showed reductions in power production (large magnitude) and muscular endurance (small magnitude), which appear to have implications for military training and risk reduction. In real-world operational applications, reduced power- and endurance-generating capabilities may be detrimental to meeting tactical requirements, making these metrics valuable for military leadership to focus on during personnel training.

Gait kinematics at trot before and after repeated ridden exercise tests in young Friesian stallions during a fatiguing 10-week training program

Background

Appropriate training is essential for equine athletes to improve fitness and ensure welfare. Young Friesian stallions must complete a 10-week training program for acceptance as breeding stallions. Earlier, this training program was demonstrated to induce overtraining.

Objectives

To evaluate how this training program affects stallions' trot locomotion variables in relation to fatigue.

Study design

Prospective analytical study.

Methods

3 or 4 years-old (n = 16) Friesian stallions performed three ridden indoor standardized exercise tests (SETs) in week-1 (SET-I; n = 15), week-6 (SET-II; n = 11) and week-10 (SET-III; n = 4), measuring heart rate (bpm) and lactate concentration (LA, mmol/L). Before and after each SET, stallions' locomotion was measured with seven inertial sensors (EquiMoves, 200 Hz) during in-hand trot on a straight line. Stride characteristics, limb angular changes, and upper body kinematics were calculated. The within-measurement coefficient of variation (CV) was calculated for all parameters. Linear mixed models were used to analyze gait variables related to SET, pre-or post-SET and a peak LA ≥4 mmol/L during SETs.

Results

Horses showed individual responses in gait kinematics to moderate fatigue. The range of motion of the withers (ROMwithers) increased post SET-II and SET-III compared to post SET-I. In horses reaching LA ≥ 4 mmol/L, CV increased post SETs for several stride characteristics and upper body asymmetry. Upper body vertical movement asymmetry was above the described reference ranges in 69% of the horses.

Main limitations

Number of horses used and only four horses managed to complete the 10-week training program as breeding stallions.

Conclusion

The young Friesian stallions showed individually different responses in absolute gait kinematics after exercise and during an intense training program. The increased ROMwithers and CV of stride characteristics after SETs suggest an acute effect of fatigue on the locomotion pattern. Further investigation is warranted for the pronounced upper body movement asymmetry related to published asymmetry reference values.

The Impact of Work-Related Musculoskeletal Pains on Routine Tasks Among Operating Room Nurses: A Multicenter Cross-Sectional Study

PURPOSE

To determine work-related musculoskeletal pain (MSP) among 105 operating room nurses (ORNs) and its effect on their routine work.

DESIGN

Multicenter cross-sectional design.

METHODS

This study was conducted with 105 nurses working in operating rooms of five different hospitals between December 15, 2021, and February 15, 2022. Data were collected using the "Nordic Musculoskeletal Questionnaire." SPSS 22.0 was used for data analysis, and a significance level of p < .05 was established.

RESULTS

Among the nurses, 75.2% were female, 78.1% had undergraduate education, and 59% worked >40 hours/week. In the previous 12 months, 69.5% of ORNs experienced lower back pain; 68.6%, neck pain; and 61.9%, back pain. The duration spent working as a scrub nurse increased the possibility of experiencing pain in the hands, wrists, back, shoulders, and lower back region (p < .05), and women had an increased risk of lower back and back pain (p < .05). Neck, lower back, back, wrist, and hand pain increased the risk of being unable to perform daily tasks (p < .05).

CONCLUSIONS

Extended work hours as a scrub nurse increase the risk of MSP, including lower back region, neck, and back pain among ORNs. Women have a higher risk of lower back and back pain. Addressing musculoskeletal issues in this profession is crucial.

CLINICAL IMPLICATIONS

Addressing musculoskeletal discomfort is vital because of its impact on nurses' job performance and potential patient harm. Providing ergonomic equipment, training nurses on musculoskeletal health, and raising awareness can help. It is also important to encourage regular breaks.

Physiological and perceptual response to critical power anchored HIIT: a sex comparison study

PURPOSE

The aim of this study was to test the hypothesis that using threshold-based high intensity interval training (HIITTHR) prescribed at an intensity above critical power (CP) in males and females matched for maximal oxygen uptake ( V ˙ O2max) (mL/kg lean mass/min) will yield no sex differences in time to fatigue.

METHODS

Thirteen males (mean ± SD: 22.0 ± 2.48 years, 181 ± 8.36 cm, 78.8 ± 11.4 kg) and eleven females (mean ± SD: 22.4 ± 2.69 years, 170 ± 5.73 cm, 65.2 ± 7.66 kg) initially undertook an incremental test to exhaustion to determine V ˙ O2max, and a CP test. Then, one HIIT session (4 min on, 2 min off) was performed to exhaustion at the work rate associated with 105%CP. Acute physiological and cardiovascular responses were recorded.

RESULTS

No sex differences were recorded in time to fatigue [Female vs. Male (min): 36.0 ± 18.5 vs. 39.3 ± 16.3], heart rate, rate of perceived exertion, or %oxygenated [haem]. Females displayed lower %deoxygenated [haem] at the end of interval 1, 2, 3, and 4 [Female vs. Male (%): 89.4 ± 21.2 vs. 110 ± 27.3, 92.0 ± 21.5 vs. 115 ± 27.6, 87.1 ± 23.7 vs. 112 ± 22.8, 88.9 ± 26.3 vs. 113 ± 23.5]. Large interindividual variability in performance, and physiological and perceptual response were present despite the use of threshold-based prescription.

CONCLUSION

The present study suggests that threshold-based prescription may help standardize the mean response exercise across sexes but does not eliminate physiological or perceptual variability. Furthermore, the lack of sex differences in TTF was accompanied by greater %deoxy[haem] in males, indicating tissue oxygenation is an unlikely determinant of HIIT performance. This study has been retrospectively registered at Trial Registration https://doi.org/10.17605/OSF.IO/KZVGC January 17th, 2023, following data collection but prior to data analyses.

Effect of increased protein intake before pre-event on muscle fatigue development and recovery in female athletes

BACKGROUND

Protein plays a vital role in facilitating muscle growth and also plays an important part in the optimal repair and recovery of the muscle after exercise. These benefits are achieved by consuming higher-protein diets. Therefore, this study aimed to investigate the effects of increased protein intake before the pre-event on muscle fatigue (MF) and ascertain if the increased protein intake before the pre-event contributes to improving recovery in female athletes.

MATERIALS AND METHODS

The experimental study was conducted at the Sports Academy for Basketball in Zagazig, Egypt, from July 2 to August 12, 2023. The study was conducted on 20 female basketball players (age: 16.65 ± 0.47 years; body height: 165.42 ± 3.09 cm; body mass: 59.68 ± 3.63 kg; training age: 2.44 ± 0.56 years). They were divided into two equally sized groups: The group with higher protein intake before the pre-event (HPP) and the group with normal protein intake before the pre-event (NPP) group. Both groups consumed the same dosage of protein (1.2 g/kg/day) as instructed (American College of Sports Medicine (ACSM) recommendation). Both groups performed the same training protocol, three times a week, over 6 weeks. All variables were assessed one week before the experimental program and after the 6-week training period. Data were collected using the Running-Based Anaerobic Sprint Test (RAST) to assess fatigue index (FI) and peak power (PP), and the Anaerobic Power Step Test to assess anaerobic capacity (AC). Moreover, changes in heart rate (HRC) to assess the recovery. The collected data were analyzed using SPSS version 22 software with the descriptive statistical test. The level of significance was set at P ≤ 0.05.

RESULTS

The results showed that both groups made significant improvements in all variables (FI-PP-AC-HRC), but the HPP group had significantly greater improvements than the NPP group. The percentage of improvement ranged from 7% to 27% for the HPP group, versus 3% to 15% for the NPP group.

CONCLUSION

The major conclusion drawn from this study was that increased protein intake before the pre-event has a positive impact on reducing MF development and enhancing recovery in female athletes.

Astrocytic calcium signals are associated with exercise-induced fatigue in mice

Exercise-induced fatigue (EF) is characterized by a decline in maximal voluntary muscle force following prolonged physical activity, influenced by both peripheral and central factors. Central fatigue involves complex interactions within the central nervous system (CNS), where astrocytes play a crucial role. This study explores the impact of astrocytic calcium signals on EF. We used adeno-associated viruses (AAV) to express GCaMP7b in astrocytes of the dorsal striatum in mice, allowing us to monitor calcium dynamics. Our findings reveal that EF significantly increases the frequency of spontaneous astrocytic calcium signals. Utilizing genetic tools to either enhance or reduce astrocytic calcium signaling, we observed corresponding decreases and increases in exercise-induced fatigue time, respectively. Furthermore, modulation of astrocytic calcium signals influenced corticostriatal synaptic plasticity, with increased signals impairing and decreased signals ameliorating long-term depression (LTD). These results highlight the pivotal role of astrocytic calcium signaling in the regulation of exercise-induced fatigue and synaptic plasticity in the striatum.

Ginsenosides, salidroside, and syringin complex exhibits anti-fatigue in exhaustive exercise rats

Excessive exercise can lead to fatigue, consequently affect exercise performance, and further have an adverse impact to human health. The synergistic effects of ginsenosides, salidroside, and syringin on improving exercise performance remain unknown. Hence, the effects of Chinese herb powder (CHP) which consisted of bioactive compounds such as ginsenosides (Rg1, Re, and Rb1), salidroside, and syringin on exercise performance, energy metabolism, tissue damage, antioxidant activity, and inflammatory cytokine were investigated in exhaustive exercise rats. Male Sprague-Dawley rats aged of 8-week-old were randomly assigned into four groups: control (normal, N), low-dose (L, 310 mg/kg bw), medium-dose (M, 620 mg/kg bw), and high-dose (H, 1550 mg/kg bw) groups. The intervention groups were orally given CHP daily for successive 30 days. Abdominal arterial blood, liver, and gastrocnemius muscles were collected 4 hours after exhaustive exercise for further analysis. The high-dose CHP group increased the time to exhaustion, decreased serum lactate level, increased serum superoxide dismutase activity, and decreased liver interleukin-6 concentration. Therefore, CHP exhibits an anti-fatigue effect for prolonging the time to exhaustion through improving lactate clearance, and to a lesser extent, enhancing the capacity of antioxidation and anti-inflammation.

A Comprehensive Dataset of Surface Electromyography and Self-Perceived Fatigue Levels for Muscle Fatigue Analysis

Muscle fatigue is a risk factor for injuries in athletes and workers. This brings relevance to the study of this biochemical process to allow for its identification and prevention. This paper presents a novel dataset for muscle fatigue analysis comprising surface electromyography data from upper-limbs and the subject's self-perceived fatigue level. This dataset contains 13 h and 20 min of data from 13 participants performing a total of 12 upper-limb dynamic movements (8 uni-articular and 4 complex/compound). This dataset may contribute to the testing of new fatigue detection algorithms and analysis of the underlying mechanisms.

Skeletal muscle adaptations and post-exertional malaise in long COVID

When acute SARS-CoV-2 infections cause symptoms that persist longer than 3 months, this condition is termed long COVID. Symptoms experienced by patients often include myalgia, fatigue, brain fog, cognitive impairments, and post-exertional malaise (PEM), which is the worsening of symptoms following mental or physical exertion. There is little consensus on the pathophysiology of exercise-induced PEM and skeletal-muscle-related symptoms. In this opinion article we highlight intrinsic mitochondrial dysfunction, endothelial abnormalities, and a muscle fiber type shift towards a more glycolytic phenotype as main contributors to the reduced exercise capacity in long COVID. The mechanistic trigger for physical exercise to induce PEM is unknown, but rapid skeletal muscle tissue damage and intramuscular infiltration of immune cells contribute to PEM-related symptoms.

Latent Space Representation of Human Movement: Assessing the Effects of Fatigue

Fatigue plays a critical role in sports science, significantly affecting recovery, training effectiveness, and overall athletic performance. Understanding and predicting fatigue is essential to optimize training, prevent overtraining, and minimize the risk of injuries. The aim of this study is to leverage Human Activity Recognition (HAR) through deep learning methods for dimensionality reduction. The use of Adversarial AutoEncoders (AAEs) is explored to assess and visualize fatigue in a two-dimensional latent space, focusing on both semi-supervised and conditional approaches. By transforming complex time-series data into this latent space, the objective is to evaluate motor changes associated with fatigue within the participants' motor control by analyzing shifts in the distribution of data points and providing a visual representation of these effects. It is hypothesized that increased fatigue will cause significant changes in point distribution, which will be analyzed using clustering techniques to identify fatigue-related patterns. The data were collected using a Wii Balance Board and three Inertial Measurement Units, which were placed on the hip and both forearms (distal part, close to the wrist) to capture dynamic and kinematic information. The participants followed a fatigue-inducing protocol that involved repeating sets of 10 repetitions of four different exercises (Squat, Right Lunge, Left Lunge, and Plank Jump) until exhaustion. Our findings indicate that the AAE models are effective in reducing data dimensionality, allowing for the visualization of fatigue's impact within a 2D latent space. The latent space representation provides insights into motor control variations, revealing patterns that can be used to monitor fatigue levels and optimize training or rehabilitation programs.

Stimulation-Induced Muscle Deformation Measured with A-Mode Ultrasound Correlates with Muscle Fatigue

Muscle fatigue is a common physiological phenomenon whose onset can impair physical performance and increase the risk of injury. Traditional assessments of muscle fatigue are primarily constrained by their dependence on maximum voluntary contractions (MVCs), which not only rely heavily on participant motivation, reducing measurement accuracy, but also require large, stationary equipment such as isokinetic dynamometers, limiting their application to discrete assessments in lab-based environments. In this work, we introduce a wearable muscle fatigue tracking strategy that employs low-profile single-element ultrasound and electrical stimulation. This integrated approach demonstrates that muscle deformation from electrically-induced muscle contractions correlates with muscle fatigue, thus circumventing the need for bulky hardware and eliminating the variability associated with human volition. We define a deformation index, which fuses stimulation-induced changes in muscle thickness with baseline muscle swelling to track muscle fatigue. Our results demonstrate that the deformation index reliably tracks muscle fatigue (r = 0.85 ± 0.15), under specific conditions, namely extended joint angles and increased stimulation, as measured by changes in knee extension torque during a series of dynamic, volitional fatiguing contractions on 8 subjects on an isokinetic dynamometer. This approach has the potential to enable real-time, semi-continuous muscle fatigue monitoring in unconstrained environments.

Critical analysis of information provided by ChatGPT on lactate, exercise, fatigue, and muscle pain: current insights and future prospects for enhancement

This study aimed to critically evaluate the information provided by ChatGPT on the role of lactate in fatigue and muscle pain during physical exercise. We inserted the prompt "What is the cause of fatigue and pain during exercise?" using ChatGPT versions 3.5 and 4o. In both versions, ChatGPT associated muscle fatigue with glycogen depletion and "lactic acid" accumulation, whereas pain was linked to processes such as inflammation and microtrauma. We deepened the investigation with ChatGPT 3.5, implementing user feedback to question the accuracy of the information about lactate. The response was then reformulated, involving a scientific debate about the true role of lactate in physical exercise and debunking the idea that it is the primary cause of muscle fatigue and pain. We also utilized the creation of a "well-crafted prompt," which included persona identification and thematic characterization, resulting in much more accurate information in both the ChatGPT 3.5 and 4o models, presenting a range of information from the physiological process of lactate to its true role in physical exercise. The results indicated that the accuracy of the responses provided by ChatGPT can vary depending on the data available in its database and, more importantly, on how the question is formulated. Therefore, it is indispensable that educators guide their students in the processes of managing the AI tool to mitigate risks of misinformation.NEW & NOTEWORTHY Generative artificial intelligence (AI), exemplified by ChatGPT, provides immediate and easily accessible answers about lactate and exercise. However, the reliability of this information may fluctuate, contingent upon the scope and intricacy of the knowledge derived from the training process before most recent update. Furthermore, a deep understanding of the basic principles of human physiology becomes crucial for the effective correction and safe use of this technology.

StressFit: a hybrid wearable physicochemical sensor suite for simultaneously measuring electromyogram and sweat cortisol

This study introduces StressFit, a novel hybrid wearable sensor system designed to simultaneously monitor electromyogram (EMG) signals and sweat cortisol levels. Our approach involves the development of a noninvasive skin patch capable of monitoring skin temperature, sweat pH, cortisol levels, and corresponding EMG signals using a combination of physical and electrochemical sensors integrated with EMG electrodes. StressFit was optimized by enhancing sensor output and mechanical resilience for practical application on curved body surfaces, ensuring accurate acquisition of cortisol, pH, body temperature, and EMG data without sensor interference. In addition, we integrated an onboard data processing unit with Internet of Things (IoT) capabilities for real-time acquisition, processing, and wireless transmission of sensor measurements. Sweat cortisol and EMG signals were measured during cycling exercises to evaluate the sensor suite's performance. Our results demonstrate an increase in sweat cortisol levels and decrease in the EMG signal's power spectral density following exercise. These findings suggest that combining sweat cortisol levels with EMG signals in real-time could serve as valuable indicators for stress assessment and early detection of abnormal physiological changes.

Neuroticism Overestimated? Neuroticism Versus Hypertonia, Pain and Rehabilitation Outcomes in Post-Spinal Cord Injury Patients Rehabilitated Conventionally and with Robotic-Assisted Gait Training

BACKGROUND

The aim of the present study was to analyse the association between neuroticism (one of the Big Five personality traits) and the most common secondary sensorimotor complications occurring in patients after spinal cord injury (SCI), i.e., muscle spasticity (hypertonia) and pain, and to investigate the associations between neuroticism and the effects of conventional rehabilitation (dynamic parapodium) and those using robotic-assisted gait training (RAGT) in this group of patients. In addition, the association of neuroticism with self-efficacy, personal beliefs about pain control, and adopted coping strategies among SCI patients was analysed. These data can be used as a reference for designing effective forms of therapy and support dedicated to this group of patients.

METHODS AND PROCEDURES

Quantitative analysis included 110 patients after SCI. The participants were divided by simple randomisation into a rehabilitation group with RAGT and a rehabilitation group with dynamic parapodium therapy (DPT). The following survey instruments were used for data collection: Revised NEO Personality Inventory (NEO-PI-R); Ashworth Scale; the Spinal Cord Independence Measure III (SCIM III); the Walking Index for Spinal Cord Injury II (WISCI-II); the American Spinal Injury Association Impairment Scale (AIS); the Pain Coping Strategies Questionnaire-CSQ; and the Beliefs about Pain Control Questionnaire-BPCQ.

OUTCOMES AND RESULTS

analyses showed a positive association between neuroticism and spastic tension (rho = 0.39; p < 0.001).

CONCLUSIONS AND IMPLICATIONS

the study showed that a high level of neuroticism correlates with a higher level of spasticity, but no such correlation was observed for pain. Additionally, the study did not show a significant correlation between neuroticism and rehabilitation outcome depending on the rehabilitation modality (RAGT vs. DPT). The results underline the importance of carrying out a psychological diagnosis of patients to provide therapeutic support in the rehabilitation process.

Circadian Rhythm and Physical Fatigue Separately Influence Cognitive and Physical Performance in Amateur Athletes

BACKGROUND/OBJECTIVES

Circadian rhythm (CR) influences various physiological functions, including physical and cognitive performance, which fluctuate throughout the day. The present study aimed to investigate the combined and separate effects of CR and physical fatigue on cognitive and physical performance.

METHODS

A sample of 18 amateur athletes was subjected to a series of tests at three different times of the day: morning, afternoon, and evening. Fatigue was induced following an isokinetic concentric exercise combined with a 20 min treadmill run, followed by assessments of selected physical and cognitive tasks.

RESULTS

A repeated measure ANOVA did not reveal an interaction between CR and fatigue in cognitive performance (p > 0.05). However, a significant main effect of fatigue was observed in visual reaction time (VisRT) across all three timepoints. Moreover, peak torque (PT) and the peak torque fatigue index (PTFI) showed significant differences between the three times of the day, peaking in the evening.

CONCLUSIONS

Although we found no interaction between CR and the physical fatigue state on selected cognitive parameters at the three times of the day, a separate effect of fatigue on cognitive performance was identified. Additionally, physical parameters exhibited peak values occurring in the evening hours. Future research should further explore underlying mechanisms that potentially influence cognitive performance at different times of the day.

Wearable heart rate sensing and critical power-based whole-body fatigue monitoring in the field

Whole-body fatigue (WBF) presents a concerning risk to construction workers, which can impact function and ultimately lead to accidents and diminished productivity. This study proposes a new WBF monitoring technique by applying the Critical Power (CP) model, a bioenergetic model, with a wrist-worn heart rate sensor. The authors modified the CP model to calculate WBF from the percentage of heart rate reserve (%HRR) and generated a personalized model via WBF perception surveys. Data were collected for two days from 33 workers at four construction sites. The results showed that the proposed technique can monitor field workers' perceived WBF with a mean absolute error of 12.8% and Spearman correlation coefficient of 0.83. This study, therefore, demonstrates the viability of wearable WBF monitoring on construction sites to support programs aimed at improving workplace safety and productivity.

The Effects of Normobaric Hypoxia on the Acute Physiological Responses to Resistance Training: A Narrative Review

ABSTRACT

Allsopp, GL, Britto, FA, Wright, CR, and Deldicque, L. The effects of normobaric hypoxia on the acute physiological responses to resistance training: a narrative review. J Strength Cond Res 38(11): 2001-2011, 2024-Athletes have used altitude training for many years as a strategy to improve endurance performance. The use of resistance training in simulated altitude (normobaric hypoxia) is a growing strategy that aims to improve the hypertrophy and strength adaptations to training. An increasing breadth of research has characterized the acute physiological responses to resistance training in hypoxia, often with the goal to elucidate the mechanisms by which hypoxia may improve the training adaptations. There is currently no consensus on the overall effectiveness of hypoxic resistance training for strength and hypertrophy adaptations, nor the underlying biochemical pathways involved. There are, however, numerous interesting physiological responses that are amplified by performing resistance training in hypoxia. These include potential changes to the energy system contribution to exercise and alterations to the level of metabolic stress, hormone and cytokine production, autonomic regulation, and other hypoxia-induced cellular pathways. This review describes the foundational exercise physiology underpinning the acute responses to resistance training in normobaric hypoxia, potential applications to clinical populations, including training considerations for athletic populations. The review also presents a summary of the ideal training parameters to promote metabolic stress and associated training adaptations. There are currently many gaps in our understanding of the physiological responses to hypoxic resistance training, partly caused by the infancy of the research field and diversity of hypoxic and training parameters.

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.

Submaximal Verification Test to Exhaustion Confirms Maximal Oxygen Uptake: Roles of Anaerobic Performance and Respiratory Muscle Strength

Background: The incremental exercise test is commonly used to measure maximal oxygen uptake (VO2max), but an additional verification test is often recommended as the "gold standard" to confirm the true VO2max. Therefore, the aim of this study was to compare the peak oxygen uptake (VO2peak) obtained in the ramp incremental exercise test and that in the verification test performed on different days at submaximal intensity. Additionally, we examined the roles of anaerobic performance and respiratory muscle strength. Methods: Sixteen physically active men participated in the study, with an average age of 22.7 ± 2.4 (years), height of 178.0 ± 7.4 (cm), and weight of 77.4 ± 7.3 (kg). They performed the three following tests on a cycle ergometer: the Wingate Anaerobic Test (WAnT), the ramp incremental exercise test (IETRAMP), and the verification test performed at an intensity of 85% (VER85) maximal power, which was obtained during the IETRAMP. Results: No significant difference was observed in the peak oxygen uptake between the IETRAMP and VER85 (p = 0.51). The coefficient of variation was 3.1% and the Bland-Altman analysis showed a high agreement. We found significant correlations between the total work performed in the IETRAMP, the anaerobic peak power (r = 0.52, p ≤ 0.05), and the total work obtained in the WAnT (r = 0.67, p ≤ 0.01). There were no significant differences in post-exercise changes in the strength of the inspiratory and expiratory muscles after the IETRAMP and the VER85. Conclusions: The submaximal intensity verification test performed on different days provided reliable values that confirmed the real VO2max, which was not limited by respiratory muscle fatigue. This verification test may be suggested for participants with a lower anaerobic mechanical performance.

Advancements in Textile-Based sEMG Sensors for Muscle Fatigue Detection: A Journey from Material Evolution to Technological Integration

Textile-based surface electromyography (sEMG) electrodes have emerged as a prominent tool in muscle fatigue assessment, marking a significant shift toward innovative, noninvasive methods. This review examines the transition from metallic fibers to novel conductive polymers, elastomers, and advanced material-based electrodes, reflecting on the rapid evolution of materials in sEMG sensor technology. It highlights the pivotal role of materials science in enhancing sensor adaptability, signal accuracy, and longevity, crucial for practical applications in health monitoring, while examining the balance of clinical precision with user comfort. Additionally, it maps the global sEMG research landscape of diverse regional contributors and their impact on technological progress, focusing on the integration of Eastern manufacturing prowess with Western technological innovations and exploring both the opportunities and challenges in this global synergy. The integration of such textile-based sEMG innovations with artificial intelligence, nanotechnology, energy harvesting, and IoT connectivity is also anticipated as future prospects. Such advancements are poised to revolutionize personalized preventive healthcare. As the exploration of textile-based sEMG electrodes continues, the transformative potential not only promises to revolutionize integrated wellness and preventive healthcare but also signifies a seamless transition from laboratory innovations to real-world applications in sports medicine, envisioning the future of truly wearable material technologies.

Activation of α7 Nicotinic Acetylcholine Receptor Improves Muscle Endurance by Upregulating Orosomucoid Expression and Glycogen Content in Mice

There are presently no acknowledged therapeutic targets or official drugs for the treatment of muscle fatigue. The alpha7 nicotinic acetylcholine receptor (α7nAChR) is expressed in skeletal muscle, with an unknown role in muscle endurance. Here, we try to explore whether α7nAChR could act as a potential therapeutic target for the treatment of muscle fatigue. Results showed that nicotine and PNU-282987 (PNU), as nonspecific and specific agonists of α7nAChR, respectively, could both significantly increase C57BL6/J mice treadmill-running time in a time- and dose-dependent manner. The improvement effect of PNU on running time and ex vivo muscle fatigue index disappeared when α7nAChR deletion. RNA sequencing revealed that the differential mRNAs affected by PNU were enriched in glycolysis/gluconeogenesis signaling pathways. Further studies found that PNU treatment significantly elevates glycogen content and ATP level in the muscle tissues of α7nAChR+/+ mice but not α7nAChR-/- mice. α7nAChR activation specifically increased endogenous glycogen-targeting protein orosomucoid (ORM) expression both in vivo skeletal muscle tissues and in vitro C2C12 skeletal muscle cells. In ORM1 deficient mice, the positive effects of PNU on running time, glycogen and ATP content, as well as muscle fatigue index, were abolished. Therefore, the activation of α7nAChR could enhance muscle endurance via elevating endogenous anti-fatigue protein ORM and might act as a promising therapeutic strategy for the treatment of muscle fatigue.

Novel Metrics for High-Density sEMG Analysis in the Time-Space Domain During Sustained Isometric Contractions

Goal: This study introduces a novel approach to examine the temporal-spatial information derived from High-Density surface Electromyography (HD-sEMG). By integrating and adapting postural control parameters into a framework for the analysis of myoelectrical activity, new metrics to evaluate muscle fatigue progression were proposed, investigating their ability to predict endurance time. Methods: Nine subjects performed a fatiguing isometric contraction of the lumbar erector spinae. Topographical amplitude maps were generated from two HD-sEMG grids. Once identified the coordinates of the muscle activity, novel metrics for quantifying the muscle spatial distribution over time were calculated. Results: Spatial metrics showed significant differences from beginning to end of the contraction, highlighting their ability of characterizing the neuromuscular adaptations in presence of fatigue. Additionally, linear regression models revealed strong correlations between these spatial metrics and endurance time. Conclusions: These innovative metrics can characterize the spatial distribution of muscle activity and predict the time of task failure.

A comparison of individual force decline profiles during a fatiguing eccentric trunk flexion and extension protocol: a pilot study

Introduction

Muscle fatigue, characterized by diminished force production and contraction sustainability, can impair muscle coordination and increase joint instability. Differing force profiles used in fatiguing tasks, such as prolonged eccentric trunk protocols, might provide insights into individualized strategies and resulting spinal stability. Thus, this study assessed individual differences in fatigue characteristics during an eccentric trunk flexion-extension protocol in a population of asymptomatic individuals.

Methods

Twelve participants (2 f/10 m, 29 ± 4 years, 78.4 ± 16.9 kg, 1.76 ± 0.10 m) performed an eccentric trunk flexion and extension protocol on an isokinetic dynamometer (45° flexion to 10° extension; 60°/s), with final analysis on 8 participants for trunk flexion and 11 for trunk extension due to data exclusions. Participants engaged in a maximal all-out (AO) task for 2 min. Each participant's torque output (Nm) was assessed on a repetition-by-repetition basis, and smoothened by a moving average of 5 repetitions. Individual time profiles for reaching fatigue thresholds (10%, 15%, 20% and 30% reduction of initial torque output), and inter subject variability (by coefficient of variation, CV in %) were assessed throughout the AO task. Further, percentage torque reduction and variability were assessed at mid (1-minute) and end (2-minute) of task.

Results

On average, for flexor and extensor muscles combined, participants reached a force reduction of 10% within 23.2 ± 19.1 s, of 15% within 44.9 ± 19.6 s, of 20% in 62.4 ± 26.3 s, and of 30% within 79.2 ± 21.8 s. The variability between individuals for the timepoint of reaching the defined torque thresholds was assessed by CV ranged between 23.4% and 103.8% for trunk flexor muscles, and between 28.4% and 56.5% for trunk extensor muscles.

Discussion

A reduction of up to 20% was seen on average for all participants within 1-minute of eccentric trunk flexion and extension. Different inter-individual force output profiles were seen throughout the AO protocol, potentially related to physiological, skill-based, technical, adaptational, and/or motivational factors. The increase in fatigue resulted in a reduction in variability among individuals. A 2-minute protocol effectively induced pronounced fatigue, offering insights into individual force profiles and strategies.

A novel kinetic model to demonstrate the independent effects of ATP and ADP/Pi concentrations on sarcomere function

Understanding muscle contraction mechanisms is a standing challenge, and one of the approaches has been to create models of the sarcomere-the basic contractile unit of striated muscle. While these models have been successful in elucidating many aspects of muscle contraction, they fall short in explaining the energetics of functional phenomena, such as rigor, and in particular, their dependence on the concentrations of the biomolecules involved in the cross-bridge cycle. Our hypothesis posits that the stochastic time delay between ATP adsorption and ADP/Pi release in the cross-bridge cycle necessitates a modeling approach where the rates of these two reaction steps are controlled by two independent parts of the total free energy change of the hydrolysis reaction. To test this hypothesis, we built a two-filament, stochastic-mechanical half-sarcomere model that separates the energetic roles of ATP and ADP/Pi in the cross-bridge cycle's free energy landscape. Our results clearly demonstrate that there is a nontrivial dependence of the cross-bridge cycle's kinetics on the independent concentrations of ATP, ADP, and Pi. The simplicity of the proposed model allows for analytical solutions of the more basic systems, which provide novel insight into the dominant mechanisms driving some of the experimentally observed contractile phenomena.

Diapocynin treatment induces functional and structural improvements in an advanced disease state in the mdx5Cv mice

Duchenne muscular dystrophy (DMD) is the most common muscular disorder affecting children. It affects nearly 1 male birth over 5000. Oxidative stress is a pervasive feature in the pathogenesis of DMD. Recent work shows that the main generators of ROS are NADPH oxidases (NOX), suggesting that they are an early and promising target in DMD. In addition, skeletal muscles of mdx mice, a murine model of DMD, overexpress NOXes. We investigated the impact of diapocynin, a dimer of the NOX inhibitor apocynin, on the chronic disease phase of mdx5Cv mice. Treatment of these mice with diapocynin from 7 to 10 months of age resulted in decreased hypertrophy of several muscles, prevented force loss induced by tetanic and eccentric contractions, improved muscle and respiratory functions, decreased fibrosis of the diaphragm and positively regulated the expression of disease modifiers. These encouraging results ensure the potential role of diapocynin in future treatment strategies.

User Perspectives and Psychophysiological Manifestations of Fatigue with Trunk Orthosis for Dystrophinopathy Patients

The chair-mounted passive trunk orthosis (CMPTO) is designed to enhance wheelchair safety for individuals with dystrophinopathy during their daily activities. Given the disease's progressive nature, it is crucial to ensure that assistive devices are carefully evaluated to prevent overexertion. This study aims to assess the CMPTO's user experience and its impact on fatigue-related psychophysiological measurements. We conducted electromyography (EMG) evaluations of four trunk muscles and assessed perceived exertion using the Borg CR-10 scale in 40 healthy subjects while they performed seated maximal reaching tasks with the CMPTO. Additionally, fifteen dystrophinopathy patients evaluated the CMPTO for usability with the System Usability Scale. Paired t-tests were employed to compare the median frequency (MDF) of EMG signals, the Wilcoxon signed-rank test for evaluating exertion, and the Mann-Whitney U test to compare the usability reported by patients to those of healthy subjects. The 4-way ANOVA revealed that MDF patterns were significantly influenced by task orientation for each muscle. The CMPTO did not cause a significant reduction in the MDF. Tasks requiring greater trunk rotation were perceived as more exhaustive. Patients reported acceptable usability with the CMPTO, with scores higher than those of healthy subjects. The CMPTO's usability was comprehensively evaluated in both healthy subjects and patients with dystrophinopathy. Our findings indicate that the CMPTO can be safely used by individuals with dystrophinopathy as an assistive device to improve seated comfort and functional abilities.

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

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

Sprint Interval Training Improves Brain-Derived Neurotropic Factor-Induced Benefits in Brain Health-A Possible Molecular Signaling Intervention

Physical exercise can significantly impact our bodies, affecting our functional capacity, structure establishment, and molecular makeup. The magnitude of these changes depends on the specific exercise protocols used. For instance, low-to-moderate-intensity exercise can activate important molecular targets in the short term, such as BDNF-mediated signaling, while high-intensity exercise can maintain these signaling molecules in the active state for a longer term. This makes it challenging to recommend specific exercises for obtaining BDNF-induced benefits. Additionally, exercise-induced molecular signaling targets can have positive and negative effects, with some exercises blunting these targets and others activating them. For example, increasing BDNF concentration through exercise can be beneficial for brain health, but it may also have a negative impact on conditions such as bipolar disorder. Therefore, a deeper understanding of a specific exercise-mediated mechanistic approach is required. This review will delve into how the sprint exercise-mediated activation of BDNF could help maintain brain health and explore potential molecular interventions.

Efficacy of amino acids in sports nutrition- review of clinical evidences

The efficacy of amino acids as popular sports supplements has triggered debates, with their impact on athletic performance varying across sports disciplines due to diversity and heterogeneity in clinical trials. This review evaluates the ergogenic potential of amino acids, by critical appraisal of results of clinical trials of Branched chain amino acids (BCAAs), arginine, glutamine, citrulline, β-alanine, and taurine, performed on elite sportsmen from various land and water sports. Clinical trials reviewed here confirm notable physiological benefits thereby supporting the claim that BCAA, citrulline and arginine in various doses can have positive effects on endurance and overall performance in sportsperson. Furthermore, results of clinical trials and metabolomic studies indicate that in future it would be more beneficial to design precise formulations to target the requirement of specific sports. For instance, some combinations of amino acids may be more suitable for long term endurance and some others may be suitable for short burst of excessive energy. The most important insights from this review are the identification of three key areas where research is urgently needed: a) Biomarkers that can identify the physiological end points and to distinguish the specific role of amino acid as anti-fatigue or reducing muscle soreness or enhancing energy b) In-depth sports-wise clinical trials on elite sportsperson to understand the ergogenic needs for the particular sports c) Design of precision formula for similar types of sports instead of common supplements.

A non-antibiotic erythromycin derivative improves muscle endurance by regulating endogenous anti-fatigue protein orosomucoid in mice

At present, there are no official approved drugs for improving muscle endurance. Our previous research found acute phase protein orosomucoid (ORM) is an endogenous anti-fatigue protein, and macrolides antibiotics erythromycin can elevate ORM level to increase muscle bioenergetics and endurance parameters. Here, we further designed, synthesized and screened a new erythromycin derivative named HMS-01, which lost its antibacterial activity in vitro and in vivo. Data showed that HMS-01 could time- and dose-dependently prolong mice forced-swimming time and running time, and improve fatigue index in isolated soleus muscle. Moreover, HMS-01 treatment could increase the glycogen content, mitochondria number and function in liver and skeletal muscle, as well as ORM level in these tissues and sera. In Orm-deficient mice, the anti-fatigue and glycogen-elevation activity of HMS-01 disappeared. Therefore, HMS-01 might act as a promising small molecule drug targeting ORM to enhance muscle endurance.

Kinematics of Two Special Endurance Trials: A Methodological Contribution to 400-m Performance

This study aimed to determine changes in the kinematics of sprint steps based on progressive muscular fatigue during high-intensity 350-m and 500-m trials. Twelve elite healthy male 400-m sprinters with a minimum of six years of regular sprint training experience were recruited. They were divided into two groups for the experiment: a 350-m and a 500-m trial group. Time and kinematics of sprinting step motion for specific segments, i.e., starting to final stages of each trial, were obtained using the Opto Jump-Microgate optical measurement system. The starting phase of each sprint was defined as the section without muscular fatigue (noF), and the final phase was the sprint under muscular fatigue (onF). Each last 25 m of the 50-m evaluated section containing ten complete running steps was selected for detailed statistical analysis. Various patterns of temporal and spatial variables of sprinting efforts were observed between 350-m and 500-m trials. Each trial result was influenced by significant individual changes (p < 0.05). All variables indicated that the two distances differed significantly in terms of running kinematics. This was confirmed by significant differences in the mean step frequency (p < 0.001), which presented a difference of 11.75%, and the mean step speed (p < 0.001). As a result of these changes, a hierarchical intermittent endurance training pattern was defined. The research concluded that special endurance (intermittent sprints) based on 350 m differed significantly in kinematics from sprints over 500 m. Therefore, it should be assumed that the distance of 350 m is more similar in its kinematics to the 400-m competition. This should encourage coaches and athletes to apply a 350-m distance in training developing special endurance, especially in the pre-competitive and competitive periods.

Impact of Pediococcus pentosaceus YF01 on the exercise capacity of mice through the regulation of oxidative stress and alteration of gut microbiota

Using treadmill training, this study replicated human exercise conditions and triggered exercise-induced fatigue in mice to examine the potential of Pediococcus pentosaceus YF01 in delaying this fatigue by regulating oxidative stress and its impact on the exercise capacity and gut microbiota of mice. The exercise capacity of mice was tested by conducting exhaustion tests, determining histopathological changes in mouse tissues, detecting the levels of serum biochemical markers, and evaluating the mRNA expression levels of relevant genes. YF01 prolonged the exhaustion time of mice, increased the serum levels of oxidative stress-related markers T-AOC, CAT, and GSH, as well as GLU and LA levels in the mice. YF01 decreased the levels of hepatic-related markers AST and ALT, as well as exercise-related markers LDH, BUN, UA, and CRE in the mice. YF01 upregulated the mRNA expression of MyHc I, SIRT1, and PGC in muscle tissues, as well as SOD1, SOD2, and CAT in both liver and muscle tissues. YF01 also downregulated the mRNA expression of MyHc IIa, MyHc IIb, and MyHc IIx in muscle tissues. Furthermore, YF01 increased the abundance of beneficial bacteria such as Lactobacillus and Lachnospiraceae in the gut microbiota of mice. In conclusion, P. pentosaceus YF01 may affect the exercise capacity of mice by modulating oxidative stress levels, thereby offering novel ideas for developing of sports science and human health.

Bioactive Compounds in Citrus reticulata Peel Are Potential Candidates for Alleviating Physical Fatigue through a Triad Approach of Network Pharmacology, Molecular Docking, and Molecular Dynamics Modeling

Physical fatigue (peripheral fatigue), which affects a considerable portion of the world population, is a decline in the ability of muscle fibers to contract effectively due to alterations in the regulatory processes of muscle action potentials. However, it lacks an efficacious therapeutic intervention. The present study explored bioactive compounds and the mechanism of action of Citrus reticulata peel (CR-P) in treating physical fatigue by utilizing network pharmacology (NP), molecular docking, and simulation-based molecular dynamics (MD). The bioactive ingredients of CR-P and prospective targets of CR-P and physical fatigue were obtained from various databases. A PPI network was generated by the STRING database, while the key overlapping targets were analyzed for enrichment by adopting KEGG and GO. The binding affinities of bioactive ingredients to the hub targets were determined by molecular docking. The results were further validated by MD simulation. Five bioactive compounds were screened, and 56 key overlapping targets were identified for CR-P and physical fatigue, whereas the hub targets with a greater degree in the PPI network were AKT1, TP53, STAT3, MTOR, KRAS, HRAS, JAK2, IL6, EGFR, and ESR1. The findings of the enrichment analysis indicated significant enrichment of the targets in three key signaling pathways, namely PI3K-AKT, MAPK, and JAK-STAT. The molecular docking and MD simulation results revealed that the bioactive compounds of CR-P exhibit a stronger affinity for interacting with the hub targets. The present work suggests that bioactive compounds of CR-P, specifically Hesperetin and Sitosterol, may ameliorate physical fatigue via the PI3K-AKT signaling pathway by targeting AKT1, KRAS, and MTOR proteins.