Muscle fatigue: what, why and how it influences muscle function

Cupping therapy does not improve quadriceps muscle pain and fatigue intensity, perceived recovery, and vertical jump height after running: A randomized clinical trial

BACKGROUND

The relationship between running training load and adaptation is complex. Cupping therapy has gained attention as a potential recovery strategy in recent years.

OBJECTIVE

To evaluate the effectiveness of cupping therapy in enhancing recovery among runners.

METHODS

A randomized clinical trial with a 72-h follow-up was conducted. The experimental group received 5 min of cupping therapy on the quadriceps, and the control group received sham hip and knee joint mobilization post-running. The outcomes evaluated were muscle pain and fatigue intensity (Numeric Visual Analog Scale), perceived recovery (Perceived Global Effect Scale), and unipodal vertical jump height (My Jump 2 app). Differences between groups were analyzed using generalized estimation equations.

RESULTS

Eighty-one recreational runners were included. No significant differences were observed between groups for muscle pain (-0.61, 95% CI: -1.35 to 0.14), fatigue intensity (-0.38, 95% CI: -1.21 to 0.45), perceived recovery (0.11, 95% CI: -0.54 to 0.75), or vertical jump height (0.75, 95% CI: -1.99 to 3.49).

CONCLUSION

Post-running cupping therapy does not improve recovery outcomes in recreational runners, raising doubts about its choice in clinical practice.

An electromyography-based multi-muscle fatigue model to investigate operational task performance

We developed a multi-muscle fatigue model (MMFM) by incorporating electromyography (EMG)-based amplitude and frequency parameters, the fast-to-slow twitch muscle fiber ratio, a time multiplier to linearize the cumulative effect of time, and a muscle multiplier to standardize the combined effect of the number of muscles being considered. We validated the model by investigating fatigue development patterns of 10 male subjects performing one sustained-till-exhaustion static and two repetitive dynamic tasks (low and high task difficulty levels) using 0.91 kg and 2.72 kg dumbbells. The results indicated that the MMFM was sensitive to fatigue-related neuromuscular changes and predicted shoulder joint fatigue accurately.

Surface Electromyography Combined with Artificial Intelligence in Predicting Neuromuscular Falls in the Elderly: A Narrative Review of Present Applications and Future Perspectives

Background: Falls among the elderly are a major public health concern, leading to increased disability and mortality. Traditional protective measures are important, but early detection and prevention are equally critical. Surface electromyography (sEMG) signals, which assess muscle electrical activity, can indicate a fall risk by detecting muscle weakness or instability. Objective: This narrative review synthesizes the research progress of sEMG in predicting neuromuscular falls among the elderly. Our goal is to explore the innovative application and development potential of the integration of sEMG and artificial intelligence (AI) in fall prevention among the elderly. Methods: A systematic search of PubMed, IEEE Xplore, and Web of Science (2013-2023) was conducted using the following keywords: artificial intelligence, wearable, sEMG, neuromuscular, and fall prediction. The inclusion criteria prioritized studies integrating sEMG with AI for elderly fall risk assessments, while non-empirical or non-English studies were excluded. Results: AI algorithms hold significant potential in medical applications, and studies on predicting neuromuscular falls in the elderly using sEMG signals have made notable progress. However, limitations include a reliance on simulated data, a lack of standardized models, sensor inaccuracies, and a focus on prediction rather than prevention. To address these challenges, this study proposes collecting authentic sEMG signals from elderly individuals with fall histories and healthy controls. By leveraging AI to develop predictive models and designing a portable sEMG acquisition and analysis system tailored for elderly communities, real-time fall risk predictions and early warnings can be achieved, thereby reducing fall incidences among the elderly. Conclusions: The combination of sEMG and AI presents a substantial promise for predicting neuromuscular falls in the elderly. Future research should prioritize validating models in real-world settings, refining sensor technology and signal processing techniques, and shifting focus toward comprehensive preventive strategies rather than mere prediction. These advancements could significantly enhance the quality of life and health outcomes of the elderly, while alleviating burdens on families and healthcare systems.

Head-neck heating and fatigue: Effects on peripheral and central function and motor accuracy in healthy men and those with multiple sclerosis

OBJECTIVE

This study aimed to evaluate whether localized heating of the head and neck, combined with prolonged submaximal exercise at a thermoneutral temperature, would elicit peripheral and central changes in healthy men and those with multiple sclerosis (MS).

METHODS

We studied the effects of head-neck heating (at 44 °C ± 0.5 °C adjacent to the skin) in men with relapsing-remitting MS (n = 16; age: 31.8 ± 7.6 years) and healthy men (n = 18; age: 27.6 ± 4.3 years). Both groups completed local heating and control trials (1-week apart) comprising 100 intermittent isometric knee extensions (5-s contraction, 20-s rest). We assessed electrically induced torque, maximal voluntary contraction (MVC), central activation ratio, muscle temperature (Tmu), perceived effort, blood stress markers, electromyography (EMG), and motor variability and accuracy. Measurements were taken at baseline, after 50 and 100 repetitions, and after 1-h recovery.

RESULTS

Local heating inhibits central activation and reduces exercise-induced peripheral fatigue compared with non-heating conditions (p < 0.05) in men with MS. Head-neck heating led to a greater increase in Tmu during exercise in both groups. During high-intensity exercise (75 % MVC), local heating increased perceived effort in men with MS, impaired accuracy in healthy men, but did not affect EMG amplitude in either group (p < 0.05). Local heating during submaximal exercise induced greater changes in central and peripheral fatigability in men with MS than in healthy men (p < 0.05).

CONCLUSION

Head-neck heating during exercise suppressed central muscle activation and reduced peripheral fatigue in men with MS more than exercise performed under non-heating conditions.

Gender differences in the impact of fatigue on lower limb landing biomechanics and their association with anterior cruciate ligament (ACL) injuries: A systematic review and meta-analysis

BACKGROUND

This meta-analysis examines the impact of neuromuscular fatigue on gender differences in lower limb landing biomechanics and its correlation with ACL injury risk.

METHODS

A comprehensive search was conducted in PubMed, Scopus, Web of Science, Embase, and the Cochrane Library up to March 2024.

RESULTS

Fourteen studies were included, averaging a quality score of 6.79; nine were high quality. Key findings: males showed a significant increase in knee flexion angle at initial contact (effect size -1.23), but females did not (-0.25). Both genders had significant changes in hip external rotation (males: 1.35, females: 1.20). Ankle peak dorsiflexion angle increased (-1.69) with no gender differences. Peak Knee extension moment increased in males (0.76) and females (0.48) with an overall effect size of 0.64, but no change in peak abduction moment. Peak Hip extension moment was significant in males (0.58) and overall (0.51), with no changes in internal rotation or adduction moments. Peak vertical ground reaction force showed no significant changes for either gender.

CONCLUSIONS

Fatigue alters knee biomechanics in males, raising ACL injury risk, and both genders show increased hip and ankle loads post-fatigue. These results suggest the need for gender-specific fatigue management strategies to mitigate ACL injury risk and call for further research into prevention mechanisms.

Quantifying voluntary knee strength deficits and muscular contribution to torque in an anterior cruciate ligament-injured adolescent population using a musculoskeletal model

BACKGROUND

Surface electromyography is commonly used to elucidate the effect of anterior cruciate ligament injury on neuromuscular function. For comparisons, electromyography is normalized to a known value, such as peak activation during maximum voluntary isometric contractions. However, a knee injury may compromise one's ability to achieve a true maximal effort. A simple musculoskeletal model may provide insight into injury related strength deficits.

METHODS

Thirty-nine anterior cruciate ligament injured adolescents (14-16 years; 25 females) and 39 matched controls (25 females) completed maximum voluntary isometric knee extension and flexion contractions on an isokinetic dynamometer. A participant-specific musculoskeletal model used normalized electromyography of knee joint muscles to determine a theoretically ideal torque for each contraction type, assuming agonist muscles were fully activated. Strength deficit ratios expressed peak experimental torque relative to theoretically ideal torque. Individual muscle contribution to experimental torque were also computed.

FINDINGS

Injured participants demonstrated significantly lower experimental torque than controls, with percent group mean difference of 17.8 % for knee extension (Injured:2.33 ± 0.89 vs Controls:2.88 ± 0.56 Nm/kg) and 16.7 % for flexion (Injured:1.22 ± 0.44 vs Controls:1.49 ± 0.27 Nm/kg). Group mean differences in strength ratios reduced to 6.3 % for extension (Injured:0.69 ± 0.11 vs Controls:0.74 ± 0.08) and 10.0 % for flexion (Injured:0.56 ± 0.15 vs Controls:0.63 ± 0.12). No between-group differences in muscular contribution to peak experimental extension torque were observed. Injured participants had lower medial gastrocnemius percent contribution to peak experimental flexion torque.

INTERPRETATION

Isometric strength tests may not adequately identify strength deficits in adolescent anterior cruciate injured populations. Simplified modelling frameworks may be more appropriate for evaluating the relationship between neuromuscular control and functional outcomes.

Effects of back muscle fatigue and modified trunk inertia on lumbar kinematics, kinetics and muscle activity during walking

Back endurance is a strong predictor of back pain, but the mechanisms underlying this relationship are not clear. Fatigue reduces muscles' force-generating capacity, so greater fatigability may increase lumbar motion and loading and trunk muscle co-contraction. Using a novel pack to modify inertia, we tested the effect of back fatigue and increased trunk inertia on lumbar kinematics, kinetics and muscle activity during walking. Lumbar kinematic and kinetic amplitudes and maximum muscle activity were measured per stride across four conditions: pre- and post-fatigue, with and without increased trunk inertia. The pack caused increases in maximum lumbar erector spinae (ES) activity by 3.19 times the average value calculated during the pre-fatigue no-pack trial (P<0.001), amplitude of lumbar flexion-extension moment by 0.0189 N m (kg g m)-1 (P<0.001), lumbar lateral bending moment by 0.0028 N m (kg g m)-1 (P=0.019) and lumbar axial rotation moment by 0.0203 N m (kg g m)-1 (P<0.001), and decreases in the amplitude of roll angle by 1.31 deg and yaw angle by 6.65 deg (both P<0.001). Back endurance is positively associated with change in maximum lumbar ES activity (r=0.69, P=0.013) and negatively associated with change in maximum rectus abdominus (RA) activity (r=-0.72, P=0.008) and lumbar flexion-extension moment amplitude (r=-0.62, P=0.031). Overall, individuals with less back endurance had increased maximum RA activity and sagittal kinetics post-fatigue whereas individuals with higher back endurance showed the opposite response. Increased RA activity with less back endurance may be a protective mechanism for stabilizing the trunk in response to increased sagittal lumbar loading due to fatigue.

Effects of fatigue on physiological, physical fitness, and stroke performance related parameters in healthy tennis players: a systematic review and meta-analysis

Fatigue is a multifactorial phenomenon involving central and peripheral mechanisms that could negatively affect performance-related measures in tennis players. The aim of this systematic review and meta-analysis was to quantify the effects of fatigue on physiological (e.g., blood lactate, heart rate), physical fitness (e.g., explosive muscle strength, speed), and stroke performance (e.g., stroke velocity or accuracy) related parameters in healthy tennis players and to provide insight into training and recovery strategies. A systematic literature search of PubMed, Web of Science, and SportDiscus identified studies that examined effects of fatigue in tennis. Inclusion criteria required that studies were conducted with healthy participants, applied fatigue-inducing interventions, and used pre-/post-test designs measuring physiological, physical, or stroke performance related parameters. Effect sizes were calculated using weighted standardized mean differences (SMD) to assess the impact of fatigue. The search identified a total of N = 642 records. Eighteen trials (318 tennis players) were included. Fatigue evoked large to moderate negative effect on physiological (SMDw = -4.19), physical fitness (SMDw = -0.74), and stroke performance (SMDw = -0.60) related parameters. The larger negative effects of fatigue on physiological and physical parameters compared to stroke performance-related outcomes indicate the importance of targeted recovery strategies (e.g., hydration, nutrition or cold baths). For stroke performance, non-fatigued states are recommended for learning new skills, while practice under fatigued conditions may help to maintain biomechanical efficiency during prolonged games.

Effects of transfer board use on physical load and transfer time in wheelchair-to-bed and bed-to-wheelchair transfers in simulated lower limb disability

This study evaluated the impact of a transfer board on reducing physical demands during wheelchair-to-bed and bed-to-wheelchair transfers. A quasi-experimental pre- and post-intervention design was conducted with 23 university students simulating individuals with disabilities after training in transfer board use. Dependent variables included cardiovascular load (heart rate), transfer time, and perceived effort (Borg scale). Using the transfer board significantly reduced cardiovascular load from 19.2% to 11.2% (p = 0.001), decreased transfer time by 23.1% (p = 0.03), and lowered perceived effort (p = 0.001). These results indicate that the transfer board enhances the efficiency and safety of transfers while significantly reducing physical strain. The findings suggest that, in the long term, this technology could help mitigate musculoskeletal risks and improve the safety and quality of life for individuals with mobility impairments and their caregivers.

Assessment of repeatability of maximal occlusal force measured at regular time intervals

STATEMENT OF PROBLEM

In recent years, there has been an increasing interest in measuring maximal occlusal force in light of the advances in digitally supported dentistry. However, studies on the assessment of changes in maximum occlusal force are sparse.

PURPOSE

The purpose of this clinical study was to assess the repeatability of maximal occlusal force measured at regular time intervals.

MATERIAL AND METHODS

One hundred participants (50 male, 50 female, aged 20 to 36 years) with a complete dentition were recruited for this study. Group 15S, 30S, 1M, and 3M repeated occlusal force measurements after 15, 30 seconds, 1 minute, or 3 minutes, 5 or 6 times, respectively. Group 8H repeated occlusal force measurements 3 times a day in the morning, afternoon, and evening with intervals of 6 to 8 hours for 5 consecutive days, 15 times in total. Two-way repeated measures ANOVA and post hoc pairwise comparison with a Bonferroni adjustment was applied to assess the measurements.

RESULTS

In general, the measurements of repetition 1 were significantly lower than of repetition 2, 3, 4, or 5 (P<.05). Within groups, participants in Group 3M showed significantly higher occlusal force measurements in repetitions 3, 4, and 5 compared with repetition 1 (P<.05). The differences in these measurements were more pronounced in male participants.

CONCLUSIONS

The maximal occlusal force measured at regular time intervals showed a lack of repeatability. The first measurement showed a statistically significantly lower value compared with the second, third, fourth, and fifth measurements in the 5 consecutive measurements. The interval between measurements significantly affected the repeatability of maximum occlusal force measurements.

Effects of localized and general fatigue on postural adjustments coupling during predictable external perturbations

PURPOSE

The central nervous system (CNS) coordinates anticipatory (APA) and compensatory postural adjustments (CPA) to face both self-induced and external perturbations. Neuromuscular fatigue (NMF), whether localized or general, impairs the CNS's ability to maintain postural stability, but the differential effects of these fatigue types on the coupling between APA and CPA remain unclear. This study aimed to investigate how localized and general NMF influence the neuromuscular control of postural adjustments during predictable external perturbations.

METHODS

Fourteen participants were exposed to two exercise protocols: intermittent isometric exercise to induce localized NMF and prolonged upper body exercise at high cardiometabolic effort to induce general NMF. Exercise intensity was monitored by measuring cardiometabolic parameters during exercise and recovery. Postural adjustments were assessed before and after NMF (recovery period) using electromyography and kinematic analyses while participants were exposed to predictable perturbations.

RESULTS

Localized NMF led to decreased muscle activation and co-activation across both fatigued and non-fatigued muscles during APA, with persistent kinematic changes in lower limb joints. In contrast, general NMF induced short-lived increases in EMG activity and co-activation, reflecting a strategic CNS adaptation to maintain stability.

CONCLUSIONS

The results suggest that localized NMF induces a more extensive and enduring impact on postural control mechanisms, likely due to altered proprioceptive feedback, whereas general NMF effects are more transient, aligning with the rapid recovery of cardiometabolic parameters. These findings highlight the CNS's role in differentially adapting postural strategies depending on the type of fatigue, with implications for understanding how fatigue impacts stability in dynamic environments.

Urologist's Fatigue and Discomfort in Different Body Regions After Performing Flexible Ureteroscopy

OBJECTIVE

To assess self-reported surgeon fatigue and discomfort in different body regions after performing flexible ureteroscopy.

METHODS

An anonymous survey was designed and distributed among urologists and trainees in four hospitals. Participants rated their discomfort in different body and hand regions as well as overall fatigue before and immediately after each flexible ureteroscopy procedure they performed.

RESULTS

The final working sample size was 45 unique surgeons (26 female and 19 male) completing 58 procedures. Respondents were 38.2 ± 14.7 years of age. Forty-two percent of respondents were male, 75% were right-hand dominant, and 25% reported existing musculoskeletal disorder. Urologists' overall fatigue score significantly increased after ureteroscopy, but females had a significantly larger increase (female β: 1.74, P <.001; male β: 0.78, P = .017). Women experienced higher discomfort in neck, upper back, right shoulder, and right elbow than men. Across different hand regions, increased post-procedural discomfort was reported mostly in the thenar area (41.8%), followed by the hypothenar area (28.5%) and thumb area (27.9%).

DISCUSSION

Urologists experience significant increase in overall fatigue and discomfort across most body and hand regions. Women seem to be disproportionally affected. Additional studies are needed to determine the causality of these findings and explore potential interventions aimed at reducing procedure-related discomfort among all urologists, especially women.

Changes in muscle oxygenation and activity during cumulative isometric muscle contraction: new insight into muscle fatigue

This study aimed to investigate the progression of muscle fatigue during submaximal efforts by examining alterations in muscle activation and oxygen saturation, employing surface electromyography ( S EMG) and near-infrared spectroscopy (NIRS) measurements. Participants performed intermittent voluntary isometric knee extension tasks at 50% of maximal voluntary contraction to induce muscle fatigue. This was conducted consecutively until they could no longer generate the target torque. Knee extension torque, S EMG, and NIRS data from the vastus lateralis were collected. Torque variability, the magnitude and frequency of the S EMG signal, and NIRS-derived parameters of the tissue oxygen saturation index (TSI) were analyzed. An increase in the magnitude (p < 0.001) and a decrease in the spectrum (p < 0.001) of the S EMG signal were observed, followed by a rise in torque variability (p < 0.001), despite the average magnitude of knee extension torque remaining constant across the trials. The NIRS measurements indicated alterations in TSI parameters, reflecting increased metabolic demand and diminished oxygen supply in the fatigued muscle (p < 0.001). Furthermore, significant interrelationships were found between changes in torque, S EMG, and NIRS variables due to the development of muscle fatigue. Our findings provide a comprehensive understanding of the development of muscle fatigue, highlighting the interconnectedness of mechanical, electrical, and metabolic responses during submaximal efforts. The reduction in force-generation capacity due to muscle fatigue is reflected in the S EMG signal and manifests as an increase in motor variability. This study identified changes in the EMG and NIRS parameters, and significant interrelation between the two metrics during the process of fatigue accumulation. These findings have the potential to provide crucial knowledge for the prediction of fatigue from either EMG signal or hemodynamic signals of the muscles.

Neuromuscular fatigability is not affected by the contraction pattern of exercises with a similar mean torque

PURPOSE

Neuromuscular fatigability is task-dependent, but the influence of the contraction pattern on neuromuscular fatigability is largely unknown. Therefore, the present study aims to investigate if neuromuscular fatigability is affected by the contraction pattern of exhausting isometric exercises.

METHODS

Thirteen participants sustained a plantar flexors MVC for 1 min (MVC1-MIN) before and after exhausting exercises designed to produce a similar mean torque (30% MVC), and following a 10-min rest period. Exercises consisted of intermittent (INT), continuous (CON) or variable (continuous contraction alternating between moderate and low intensity, VAR) contractions performed until task failure.

RESULTS

The INT resulted in greater exercise duration and torque-time integral than CON and VAR. MVC similarly decreased after all exercises due to neural and muscular impairments. The torque loss during the MVC1-MIN increased after all exercises to a similar extent, mainly because of neural alterations. Contrary to MVC, the torque loss during the MVC1-MIN returned to baseline value after the recovery period.

CONCLUSION

INT, CON and VAR exercises, performed with identical mean torque and until exhaustion, led to a similar neuromuscular fatigability. When the mean torque is matched among exercises, the contraction pattern does not influence the extent of neuromuscular fatigability, assessed through the maximal torque production and sustainability. The present findings are crucial to consider for the management of neuromuscular fatigability in physical conditioning in both athletes and patients.

The Effect of Tissue Stretching and Release Strategies on Neck Muscles Fatigue and Pain Intensity in Office Workers Affected by Chronic Neck Pain: A Rater-Blind, Semi-Experimental Study

Background and Aims

Nonspecific chronic neck pain (ns-CNP) is a common cause of disability among office workers. However, the effectiveness of tissue release and stretching strategies in managing pain and fatigue of neck muscles in employees affected by ns-CNP has not been assessed.

Methods

Thirty-nine employees who suffered from ns-CNP were randomly assigned to stretching, tissue release interventions or control group (n = 13). Neck pain and fatigue in neck extensors, upper trapezius, and sternocleidomastoid muscles were measured during 40 min of typing with a 45-degree head flexion at baseline and immediately after a 6-week intervention using visual analog scale and surface electromyography.

Results

Pain significantly decreased after 6 weeks of both interventions (p < 0.05). There were no significant within-group differences for right cervical muscle fatigue in the intervention groups, but a significant difference was noted in the control group at the 25th and 40th minutes (p < 0.05). Additionally, a significant difference was observed between the release and control group at the 30th, 35th, and 40th minutes (p < 0.05). Left cervical muscle fatigue significantly decreased at the 25th and 40th minutes only for the release group (p < 0.05). A significant difference was observed between the release and control groups at the 40th minute for the right upper trapezius (p < 0.05).

Conclusion

Only the stretching group showed a significant difference with the control in the left sternocleidomastoid at the 10th and 15th minutes, and the release group with the control in the last 5-min. Stretching and release interventions could control neck pain and muscle fatigue in the 45-degree head flexion position.

Dry Needling in Sports and Sport Recovery: A Systematic Review with an Evidence Gap Map

BACKGROUND

Dry needling is an increasingly popular technique used in sports and regenerative medicine contexts. However, there is no comprehensive overview of investigations of dry needling in sports and sport recovery.

OBJECTIVES

The objectives were to perform a systematic review of dry needling in sports athletes with an evidence gap map, to identify current gaps in the literature, and to provide stakeholders with direction for future research.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) 2020 guidelines were followed. Studies on healthy and injured athletes receiving dry needling were included. Three databases (PubMed, Scopus, and Web of Science) were searched, data were synthesized narratively, key data were summarized quantitatively, and an evidence gap map was created.

RESULTS

The authors incorporated 24 studies into the current study, encompassing 580 athletes, predominantly involving talent/developmental and highly trained/national-level athletes across 13 sports. Most studies used passive or placebo controls, with 37.5% incorporating active controls. Interventions focused mainly on the lower limbs (58.3%). Around 69% of studies reported pain perception outcomes, while six examined muscular strength, activity, and range of motion. While results varied, dry needling generally showed a more positive effect on pain than on athletic performance.

CONCLUSIONS

Dry needling studies seem to describe general effectiveness and safety for reducing pain and muscle stiffness in a wide variety of body regions. However, further research is needed on underrepresented populations such as elite, world-class, and Paralympic athletes, as well as expanding investigations into long-term effects and a broader range of muscle groups, particularly the hamstrings. The results may be valuable for medical professionals, sports medicine specialists, and researchers.

REGISTRATION

OSF project no.: osf.io osf.io/h3yeq.

Acute acetaminophen ingestion improves the recovery of neuromuscular fatigue following simulated soccer match-play

OBJECTIVES

This study aimed to investigate the impact of acute acetaminophen ingestion on the responses of neuromuscular function, biomarkers of muscle damage, and physical performance during the 72-hour recovery period following simulated soccer match-play.

DESIGN

The study followed a crossover randomized, double-blind, placebo-controlled trial design.

METHODS

During the two experimental sessions, thirteen semi-professional male soccer players completed a 90-minute simulated soccer match, 60 min after oral ingestion of 1 g acetaminophen or placebo. Maximal voluntary contraction and twitch responses of the knee extensor muscles, elicited through electrical femoral nerve stimulation, were utilized to evaluate both peripheral fatigue (potentiated twitch force, Qtw,pot) and central fatigue (voluntary activation). Performance was assessed through countermovement jump and 20 m sprint tests. Creatine kinase and lactate dehydrogenase were also measured.

RESULTS

Smaller reductions were observed in maximal voluntary contraction (-13.3 ± 7.5 % vs. -24.7 ± 11.1 %) and voluntary activation (-3.8 ± 4.4 % vs. -12.9 ± 5.4 %) in the acetaminophen compared to the placebo condition immediately after simulated soccer match-play (p < 0.05). Afterward, these parameters were recovered 24 h earlier in the acetaminophen session compared to the placebo session. Furthermore, the 20 m sprint performance was significantly better throughout the recovery period in the acetaminophen session compared to the placebo session.

CONCLUSIONS

The findings of this study showed that acute ingestion of 1 g of acetaminophen (1 h before exercise) attenuated the decrease in maximal voluntary contraction and voluntary activation levels after exercise, as well as improved 20 m sprint performance.

Eicosapentaenoic Acid and Medium-Chain Triacylglycerol Structured Lipid Supplementation Improves Muscular Endurance Exercise Performance and Reduces Muscle Fatigue in Young Healthy Male

OBJECTIVE

Structured lipids containing medium-chain fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) from fish oil (EPA/MCT) and it improve overall endurance. However, their effects on local muscle endurance remain unclear. This study aimed to investigate the effects of EPA/MCT intake on muscle endurance during leg extension exercises and subsequent muscle fatigue.

METHODS

This 8-week, placebo-controlled, randomized, double-blind parallel-group trial involved 20 healthy young men. Subjects were randomly assigned to an EPA/MCT group (10 subjects) and a placebo group (PL group, 10 subjects). They consumed 4560 mg of the test food daily for 8 wk before an exercise intervention. The EPA/MCT supplement contained 600 mg of EPA, 260 mg of DHA, and 1890 mg of MCT (1110 mg of octanoic acid and 780 mg of decanoic acid). After the 8-week intervention, the subjects performed four sets of leg extension exercises at 40% of their body weight until exhaustion. The number of repetitions per set and the total repetitions across the four sets served as indicators of muscle endurance. Isometric maximum voluntary contraction (MVC), range of motion, circumference, muscle thickness, echo intensity, and muscle stiffness were measured before and after exercise to assess muscle fatigue.

RESULTS

There was no difference between the groups in the number of repetitions for sets 1-4 or in the total number of repetitions during the leg extension exercise. In the EPA/MCT group, a significant negative correlation was observed between the increase in the blood EPA/AA ratio and the rate of decrease in the number of repetitions. Additionally, the decrease in MVC after exercise was significantly smaller in the EPA/MCT group than in the PL group.

CONCLUSION

Our study results suggest that an 8-week intake of EPA/MCT can increase the blood EPA/AA ratio and improve muscle endurance performance. Additionally, EPA/MCT intake reduces muscle fatigue after exercise.

Diaphragm Fatigue Does Not Impact Breathing Mechanics or Function in People with Chronic Low Back Pain

Background and Objective

The diaphragm is an important respiratory muscle that also plays a crucial role in developing intra-abdominal pressure and assisting in spinal stability. Chronic low back pain (CLBP) is a complex musculoskeletal condition and has been associated with respiratory problems and altered breathing mechanics. The purpose of this comparative cross-sectional study is to investigate whether diaphragm fatigue affects breathing mechanics and function in individuals with CLBP.

Methods

Volunteers were recruited between the ages of 35-65 years old with and without CLBP. Participants performed 30 minutes of exercises intended to fatigue the diaphragm. The following respiratory parameters were measured: Breathing mechanics (chest and abdominal movement and respiratory rate), diaphragm function (forced expiratory volume in 1 second (FEV1) using a handheld spirometer), and diaphragm movement as measured by sub-diaphragm (L1 to diaphragm domes) volume changes at the end of exhalation and inhalation using MRI scans.

Results

A total of 36 participants were recruited (n = 21M; n = 15F), with 18 participants suffering from CLBP (n = 10M; 8F) and 18 participants serving as a comparison group (n = 11M; n = 7F). There were no differences in breathing mechanics, diaphragm function or excursion (volumetrics) between people with and without CLBP after 30 minutes of exercises intended to fatigue the diaphragm.

Conclusion

The lack of differences suggests that the diaphragm, regardless of its fatigue status as a spinal stabilizer, will not relinquish or weaken its function as a breathing muscle, though it may be less effective as a spinal stabilizer. Individuals with chronic or recurrent low back pain might therefore be more susceptible to subsequent pain flare-ups than non-symptomatic individuals. A potential clinical implication of these findings is that incorporating diaphragmatic breathing exercises to enhance diaphragm function may offer an effective treatment option for patients with CLBP.

Changes in shooting accuracy among basketball players under fatigue: a systematic review and meta-analysis

Objective

To investigate the influence of physical and mental fatigue of different intensities (mild, moderate or severe) on basketball shooting accuracy, with the aim of informing more effective training protocols and competition strategies.

Methods

Literature searches were conducted on Web of Science, PubMed, and EBSCO databases up to 25 June 2024. Inclusion and exclusion criteria were specified, and data extraction sheets were prepared. Study quality was assessed by using the Cochrane Risk of Bias Tool in Review Manager 5.4, and Stata18.0 software was used for heterogeneity analysis, subgroup analysis, forest plots, stratification analysis, and bias assessment.

Results

Moderate physical fatigue affected two-point shooting accuracy (P < 0.01),severe physical fatigue affected both two-point (P = 0.02) and three-point shooting accuracy (p < 0.01),with severe physical fatigue showing a greater detrimental impact on three-point shooting accuracy, while two-point shooting accuracy may vary under specific conditions. Additionally, adolescent athletes were less affected by severe physical fatigue compared to adult athletes or those with longer training experience. Moderate mental fatigue also significantly reduced free-throw accuracy (p < 0.01).

Conclusion

The shooting accuracy of basketball players was significantly affected by moderate and severe physical fatigue. Severe physical fatigue notably adversely affected the accuracy of three-point shooting relative to moderate fatigue; Additionally, moderate mental fatigue significantly reduced free-throw accuracy, which may be attributed to a decline in cognitive executive functions, highlighting the importance of fatigue management in sports training.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/#myprospero, identifier CRD42024539553.

Elastic textile-based wearable modulation of musculoskeletal load: A comprehensive review of passive exosuits and resistance clothing

Elastic textiles play a critical role in passive wearable solutions for musculoskeletal load management in both passive exosuits and resistance clothing. These textiles, based on their ability to stretch and retract, can exhibit ambivalence in their load-modulating effects when used in occupational, rehabilitation, exercise, or everyday activity settings. While passive exosuits and resistance garments may appear similar in design, they have opposing goals: to reduce the musculoskeletal load in the case of exosuits and to increase it in the case of resistance clothing. Despite this intrinsic connection, these two approaches have not been extensively linked together. This review aims to fill this gap by examining the common and distinct principles of elastic textiles in passive exosuits and resistance clothing, shedding light on their interactions and the complex dynamics of musculoskeletal load systems. The effectiveness of different designs in passive exosuits that mimic musculoskeletal function and resistance clothing that increase the workload for strength training are critically reviewed. Current challenges in practical implementation and opportunities to improve critical issues, such as preload, thermal comfort, skin friction, and donning and doffing are also highlighted.

Different Spatial Characteristic Changes in Lumbopelvic Kinematics Before and After Fatigue: Comparison Between People with and Without Low Back Pain

BACKGROUND

The lumbopelvic region plays a pivotal role in enabling various functional activities. This study quantified and compared the kinematic changes between healthy individuals and patients with recurrent low back pain (LBP) in both rested and fatigued states to gain insight into the kinematic adaptation and mechanisms underlying kinematic variations that occur in the presence of these factors.

METHODS

Participants were divided into two groups: the LBP (n = 23) and healthy control groups (n = 19). Dynamic lumbopelvic measurements were taken using a biplane radiography image system while the participants performed weight-bearing forward-backward bending before and after fatigue. All lumbopelvic kinematics were described as the three-dimensional motion of the vertebra relative to the pelvis and were measured at normalized time intervals from maximum extension to approximately 45° of flexion.

RESULTS

Repetitive lifting- and lowering-induced fatigue significantly affected lumbopelvic kinematics in the anterior/posterior translation (mm) and rotation around the z-axis in both healthy individuals and patients with LBP (p < 0.05). In healthy individuals, significant differences occurred in approximately 13-83% of the forward-backward bending cycle (0-100%), whereas, in patients with LBP, significant differences mainly occurred in 61-93% of the cycle (p < 0.01).

CONCLUSIONS

The lumbopelvic kinematic changes observed in both LBP patients and healthy individuals after fatigue may indicate protective compensation or vulnerability and could play a role in LBP dysfunction.

Age- and sex-specific differences in repetitive sprinting in 9-14-year-olds living in Turkey

BACKGROUND

Since children's daily activities are mostly anaerobic, it is important to assess anaerobic performance as part of the physical assessment. Therefore, running speed, power, and heart rate during repetitive sprints were investigated.

METHOD

A total of 118 children participated (mean age:11.5 range 9-14y; 48% boys, 52% girls) and performed the children's repetitive and intermittent sprinting performance (CRISP) test, which consists of six sprint runs performed at maximal speed over 30-meter with short recovery periods (10 s) between each run. GLM Repeated Measures were used to examine the effect of runs (within-subject factor) and age and sex (between-subject factor) and as well as possible interactions for running time, power, and heart rate.

RESULTS

Running times increased significantly across runs (p < 0.001, large effect size), showing a non-linear slowdown (p = 0.013). Also, a main effect of age, [p < 0.033] and sex [p < 0.011, medium effect size] emerged. However, interaction effects showed that girls fatigued more in the second half of the test, which led to larger differences with the boys in the later runs of the CRISP. Moreover, the interaction effect of age-by-run-by-sex was found. Eleven-year-old children had the longest running times. At the same time, young children, predominantly boys, showed less fatigue, as their last runs were comparable in time to the first ones. Analysis of the power showed a main effect of age, indicating more power in older children [p < 0.001, large effect size], especially after 11 years. No differences between sexes were found for power. Heart rate increased significantly during the repetitive sprinting [p < 0.001, large effect size]. No differences for age or sex were found for mean or peak heart rate.

CONCLUSION

The CRISP test is sensitive to running fatigue [large effect size] and distinguishes between the performance characteristics of children according to age and sex. Running speed and power go up between 12 and 14 years. Girls run slower but generate comparable power over the runs. Yet they fatigue more in the second half of the test than boys.

Mechanical power distribution of the lower limbs changed during intermittent 300 countermovement jumps

PURPOSE

The aim of this study was to investigate the effect of 300 intermittent countermovement jumps (CMJs) on the mechanical power distribution at the joints of the lower limbs and the influence of the upper body to explain vertical jump performance.

METHODS

Fifteen male sport students (age 24.5 ± 2.3 years; body height 1.85 ± 0.06 m; body mass 84.8 ± 8.5 kg) performed a set of intermittent 300 CMJs at maximal effort. An inverse-dynamic approach was used to calculate the mechanical power at the hip, knee, and ankle joint for each jump.

RESULTS

Jump height and mechanical power in the knee and ankle joints decreased significantly (p < .010), while remained the same in the hip joint. In contrast, a significant increased vertical velocity was observed for the upper body segment. In addition, a significant higher angular momentum at the center of mass was detected during the braking and propulsion phase.

CONCLUSION

The findings highlight a fatigue-related decrease in lower limb power, particularly in the knee and ankle joints, which changed the mechanical power distribution at the joints of the lower limbs. The trunk extensor muscles were probably able to counteract the fatigue-related decrease in lower limb power by increased vertical velocity of the upper body segment and higher angular momentum at the center of mass during the braking and propulsion phase. Accordingly, the most effective way to maintain jumping performance in fatigued state would be to improve the fatigue resistance of the knee extensors, ankle plantar flexors, and trunk extensor muscles.

A Novel Passive Occupational Shoulder Exoskeleton With Adjustable Peak Assistive Torque Angle for Overhead Tasks

OBJECTIVE

Overhead tasks are a primary inducement to work-related musculoskeletal disorders. Aiming to reduce shoulder physical loads, passive shoulder exoskeletons are increasingly prevalent in the industry due to their lightweight, affordability, and effectiveness. However, they can only handle specific tasks and struggle to balance compactness with a sufficient range of motion effectively.

METHOD

We proposed a novel passive occupational shoulder exoskeleton designed to handle various overhead tasks at different arm elevation angles, ensuring sufficient ROM while maintaining compactness. By formulating kinematic models and simulations, an ergonomic shoulder structure was developed. Then, we presented a torque generator equipped with an adjustable peak assistive torque angle to switch between low and high assistance phases through a passive clutch mechanism. Ten healthy participants were recruited to validate its functionality by performing the screwing task.

RESULTS

Measured range of motion results demonstrated that the exoskeleton can ensure a sufficient ROM in both sagittal (164) and horizontal (158) flexion/extension movements. The experimental results of the screwing task showed that the exoskeleton could reduce muscle activation (up to 49.6), perceived effort and frustration, and provide an improved user experience (scored 79.7 out of 100).

CONCLUSION

These results indicate that the proposed exoskeleton can guarantee natural movements and provide efficient assistance during overhead work, and thus have the potential to reduce the risk of musculoskeletal disorders.

SIGNIFICANCE

The proposed exoskeleton provides insights into multi-task adaptability and efficient assistance, highlighting the potential for expanding the application of exoskeletons.

Observing changes in motoneuron characteristics following distorted sensorimotor input via blood flow restriction

Disruption of the blood supply to a limb in conjunction with active movement boosts muscle growth, aids in rehabilitation, and allows controlled exploration of the sensorimotor system. Yet, the underlying neuromechanical changes have not been observed in great detail. This study aims to report the acute neuromuscular effects of temporary blood flow restriction (BFR) through behavioral changes at the level of motor units (MUs) using high-density surface electromyography on the abductor digiti minimi muscle during 20 trapezoidal and sinusoidal isometric force tracking tasks (5 pre-BFR, 5 during BFR, and 10 post-BFR). Unsurprisingly, during BFR, reported discomfort levels increased significantly (ρ < 0.001) regardless of the task (+239% trapezoidal, +228% sinusoidal). However, BFR had very little impact on task tracking performance, though the reconstructed force derived from the underlying neural drive (smoothed cumulative spike train of MUs) deviated substantially during BFR (-40% in trapezoidal, -47% in sinusoidal). Regardless of the condition, the numbers of extracted MUs were consistent (20-26 in trapezoidal, 23-29 in sinusoidal). Interestingly, the interspike interval (ISI) of these units increased by 28% in trapezoidal and 24% in sinusoidal tasks during BFR, with ISI steadily returning to original values post-BFR. These results indicate that acute BFR transiently alters the active MU pool, and MU firing behavior, yet only slightly affects the resulting task performance. However, pre-BFR motor function is gradually restored after BFR release. These findings provide insights into the resulting effects of acute BFR administration and the complex response it elicits from the sensorimotor system.NEW & NOTEWORTHY To improve our understanding of how acute blood flow restriction (BFR) intervention affects neuromechanical function and motor unit characteristics, we applied high-density surface electromyography on the abductor digiti minimi muscle during isometric trapezoidal and sinusoidal precision force tracking tasks. Although BFR increased discomfort, it minimally affected force tracking performance; however, it did alter the underlying motor unit behavior. These findings further enhance our understanding of the neural mechanisms underlying BFR.

Association between periodontitis and physical fitness in law enforcement workers

OBJECTIVES

Oral and periodontal health have been linked to systemic health, cardiovascular disease and inflammation markers. Physical fitness has been linked to increased inflammatory response, but only few studies have investigated the association between oral health with physical activity. The aim of this study was to evaluate the association between oral and periodontal health status and physical fitness in British law enforcement workers.

METHODS

89 subjects were recruited between November and December 2019. Cardiopulmonary fitness was measured by Maximal Oxygen Uptake (VO2max) (ml/kg/min) and Maximum Load (Loadmax) (W) generated at the end of the Bruce incremental treadmill test; physical activity levels through accelerometers; functional strength tests by Countermovement Jump (CMJ) Power (W) and Height (cm) average. Oral variables included percentage of sites with PPD > 4 mm (% PPD > 4), full-mouth bleeding score (FMBS) and Decayed, Missing, and Filled Teeth (DMFT) index. Linear regression models were adjusted for age, gender and fat %.

RESULTS

Mean age was 41.5 years (range 23-61; 71.9% male). Higher % PPD > 4 was consistently correlated with lower Loadmax (-4.96; p = 0.092), CMJ Height average (-0.39; p = 0.064), and press-ups in 60 s (-0.85; p = 0.052) though the associations were not statistically significant. FMBS was associated with the % of a day spent in sedentary (0.78; p = 0.030) and light activities (-0.75; p = 0.022).

CONCLUSIONS

Periodontitis may be negatively associated with certain components of physical performance.

CLINICAL RELEVANCE

Oral health status may be associated with physical fitness and functional strength.

Fusion of EEG and EMG signals for detecting pre-movement intention of sitting and standing in healthy individuals and patients with spinal cord injury

Introduction

Rehabilitation devices assist individuals with movement disorders by supporting daily activities and facilitating effective rehabilitation training. Accurate and early motor intention detection is vital for real-time device applications. However, traditional methods of motor intention detection often rely on single-mode signals, such as EEG or EMG alone, which can be limited by low signal quality and reduced stability. This study proposes a multimodal fusion method based on EEG-EMG functional connectivity to detect sitting and standing intentions before movement execution, enabling timely intervention and reducing latency in rehabilitation devices.

Methods

Eight healthy subjects and five spinal cord injury (SCI) patients performed cue-based sit-to-stand and stand-to-sit transition tasks while EEG and EMG data were recorded simultaneously. We constructed EEG-EMG functional connectivity networks using data epochs from the 1.5-s period prior to movement onset. Pairwise spatial filters were then designed to extract discriminative spatial network topologies. Each filter paired with a support vector machine classifier to classify future movements into one of three classes: sit-to-stand, stand-to-sit, or rest. The final prediction was determined using a majority voting scheme.

Results

Among the three functional connectivity methods investigated-coherence, Pearson correlation coefficient and mutual information (MI)-the MI-based EEG-EMG network showed the highest decoding performance (94.33%), outperforming both EEG (73.89%) and EMG (89.16%). The robustness of the fusion method was further validated through a fatigue training experiment with healthy subjects. The fusion method achieved 92.87% accuracy during the post-fatigue stage, with no significant difference compared to the pre-fatigue stage (p > 0.05). Additionally, the proposed method using pre-movement windows achieved accuracy comparable to trans-movement windows (p > 0.05 for both pre- and post-fatigue stages). For the SCI patients, the fusion method showed improved accuracy, achieving 87.54% compared to single- modality methods (EEG: 83.03%, EMG: 84.13%), suggesting that the fusion method could be promising for practical rehabilitation applications.

Conclusion

Our results demonstrated that the proposed multimodal fusion method significantly enhances the performance of detecting human motor intentions. By enabling early detection of sitting and standing intentions, this method holds the potential to offer more accurate and timely interventions within rehabilitation systems.

Premovement activity in the corticospinal tract is amplified by the placebo effect: an active inference account

The aim of this study is to investigate whether expectancy, induced through a placebo procedure, favors the activation of the corticospinal tract before movement initiation. By adopting the premovement facilitation paradigm, we applied transcranial magnetic stimulation over the left or right primary motor cortex at rest and 100 ms or 50 ms before movement onset while healthy volunteers performed a reaction time (RT) motor task consisting of abductions of the right or left thumb after a go signal. Participants in the placebo group received an inert electrical device applied on the right forearm along with information on its speed-enhancing properties. A control group received the same device with overt information about its inert nature, while another control group underwent no intervention. Along with RT, we measured the amplitude of the motor evoked potential (MEP) before and after the procedure. Compared to the control groups, the placebo group had faster RT and greater MEP amplitude before movement initiation. This study demonstrates that the placebo effect can boost the activity of the corticospinal tract before movement onset, and this modulation positively impacts motor performance. These results give experimental support to the active inference account.

Development of an Alternative Protocol to Study Muscle Fatigue

When measuring real-time in vivo muscle fatigue with electromyography (EMG), data collection can be compromised by premature sensor removal or environmental noise; therefore, the objective of this study was to develop a postmortem in vivo methodology to induce muscle fatigue and measure it using EMG. Barrows (N = 20) were stratified by weight and randomly allocated into one of two treatments. The treatments consisted of barrows being subjected to a hog electric stunner super-contraction cycle (ES) or not (CON) postmortem. The right hind limb bicep femoris (BF) and semitendinosus (ST) were selected for ambulatory movement simulation using electronic muscle stimulation (EMS). Muscle workload during EMS was measured with EMG using median power frequency (MdPF) and root mean square (RMS) as indicators of action potential velocity and muscle fiber recruitment. Ambulatory movement was induced and recorded for 20 min with a 4:4 duty cycle at 70 Hz. Muscle biopsies were collected pre- and post-EMS for metabolite analyses to corroborate muscle fatigue onset. There was a TRT × Muscle interaction for normalized RMS percentage (p < 0.01), where BF from CON barrows had greater values (p < 0.01). There were no interactions or TRT main effects for the MdPF normalized value (p ≥ 0.25), but there were Period and muscle effects on MdPF (p < 0.01). Bicep femoris had smaller (p < 0.01) MdPF than ST. The percentage of MdPF decreased (p < 0.01) by Period 5 compared to the other Periods, which did not differ from each other (p ≥ 0.38). There were TRT × Muscle and Muscle × Period interactions for ATP muscle concentration (p ≤ 0.03). The concentration of CON BF ATP was greater (p < 0.01) than that of ES BF and CON and ES ST, which did not differ from each other (p ≥ 0.11), but the APT concentration tended to differ between ES BF and ES ST (p = 0.06). Semitendinosus ATP concentration decreased (p < 0.01) post-EMS compared to ST pre- and BF pre- and post-EMS (p ≥ 0.29), but BF and ST concentration tended to differ pre-EMS (p = 0.07). The data indicated that EMS is a valuable tool for replicating ambulatory movement or physical activity, but super-contraction is not a means to accelerate postmortem muscle fatigue onset. Therefore, further refinement, such as longer EMS stimulation time, should be considered.

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.

Forearm elevation impairs local static handgrip endurance likely through reduction in vascular conductance and perfusion pressure: revisiting Rohmert's curve

Maximal isometric contraction time (MICT) is critical for most motor tasks and depends on skeletal muscle blood flow at < 40% of maximal voluntary strength (MVC). Whether limb work positions associated with reduced perfusion pressure and facilitated vessel compression affect MICT is largely unknown. In 14 healthy young men we therefore assessed bilateral handgrip MICT at 15, 20, 30, 40, and 70% of MVC in horizontal forearm positions of 0.0, + 27.5 or - 27.5 cm relative to heart level. Forearm blood flow (FBF, venous occlusion plethysmography) and brachial blood pressure were measured repetitively. MICT at 15% MVC was significantly shorter by 66.3 and 86.2 s with forearm position + 27.5 cm (389.6 ± 23.3 s) as compared to 0.0 cm (455.9 ± 34.1 s) and - 27.5 cm (475.8 ± 35.0 s) while MICT at 20-70% MVC was unaffected. Peak FBF at 15% MVC was significantly lower in position + 27.5 cm (11.11 ± 0.92 ml/min/100 ml) compared to 0.0 cm (15.55 ± 0.91 ml/min/100 ml) or - 27.5 cm (14.21 ± 0.59 ml/min/100 ml) and vascular resistance significantly higher in position + 27.5 vs 0.0 or - 27.5 cm. Working position above, but not below heart level may limit MICT at 15% MVC possibly through blood flow reduction arising from increased vascular resistance beside reduced perfusion pressure. Local isometric endurance warrants (re)evaluation regarding hydrostatic/gravitational or other hemodynamic limitations.

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

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

Effectiveness of Using a Digital Wearable Plantar Pressure Device to Detect Muscle Fatigue: Within-Subject, Repeated Measures Experimental Design

Background

Muscle fatigue, characterized by reduced force generation during repetitive contractions, impacts older adults doing daily activities and athletes during sports activities. While various sensors detect muscle fatigue via muscle activity, biochemical markers, and kinematic parameters, a real-time wearable solution with high usability remains limited. Plantar pressure monitoring detects muscle fatigue through foot loading changes, seamlessly integrating into footwear to improve the usability and compliance for home-based monitoring.

Objective

This study aimed to investigate the effects of muscle fatigue on plantar pressure measurements using a self-developed wearable plantar pressure system.

Methods

Twelve healthy participants completed a 5-minute calf muscle fatigue protocol. The plantar pressures and surface electromyography (sEMG) activity of the gastrocnemius muscles were recorded before and after exercise. The plantar pressures at 6 regions and the median frequency (MDF) of sEMG were analyzed to quantify fatigue.

Results

The self-developed foot pressure system showed a significant decrease in plantar pressure peak values at the heel of the left (P=.003) and right feet (P=.001) and at the lateral toe of the left (P=.001) and right feet (P=.026). A significant increase was observed at the metatarsal head of both the left foot (P=.001) and the right foot (P=.017). The MDF of sEMG signals significantly decreased in the left (P=.001) and right gastrocnemius (P<.001).

Conclusions

Plantar pressure changes and sEMG signals effectively detect gastrocnemius muscle fatigue using the proposed wearable system, supporting the development of a wearable solution for detecting muscle fatigue suitable for home-use.

Fatigue assessment in distance runners: A scoping review of inertial sensor-based biomechanical outcomes and their relation to fatigue markers and assessment conditions

BACKGROUND

Fatigue manifests as a decline in performance during high-intensity and prolonged exercise. With technological advancements and the increasing adoption of inertial measurement units (IMUs) in sports biomechanics, there is an opportunity to enhance our understanding of running-related fatigue beyond controlled laboratory environments.

RESEARCH QUESTION

How have IMUs have been used to assess running biomechanics under fatiguing conditions?

METHODS

Following the PRISMA-ScR guidelines, our literature search covered six databases without date restrictions until September 2024. The Population, Concept, and Context criteria were used: Population (distance runners ranging from novice to competitive), Concept (fatigue induced by running a distance over 400 m), Context (assessment of fatigue using accelerometer, gyroscope, and/or magnetometer wearable devices). Biomechanical outcomes were extracted and synthesised, and interpreted in the context of three main study characteristics (cohort ability, testing environment, and the inclusion of physiological outcomes) to explore their potential role in influencing outcomes.

RESULTS

A total of 88 articles were included in the review. There was a high prevalence of treadmill-based studies (n=46, 52%), utilising only 1-2 sensors (n=69, 78%), and cohorts ranged in experience, from sedentary to elite-level runners, and were largely comprised of males (69% of all participants). The majority of biomechanical outcomes assessed showed varying responses to fatigue across studies, likely attributable to individual variability, exercise intensity, and differences in fatigue protocol settings and prescriptions. Spatiotemporal outcomes such as stride time and frequency (n=37, 42 %) and impact accelerations (n=55, 62%) were more widely assessed, with a fatigue response that appeared population and environment specific.

SIGNIFICANCE

There was notable heterogeneity in the IMU-based biomechanical outcomes and methods evaluated in this review. The review findings emphasise the need for standardisation of IMU-based outcomes and fatigue protocols to promote interpretable metrics and facilitate inter-study comparisons.

The effects of sex and contraction intensity on fatigability and muscle oxygenation in trained individuals

Fatigability varies depending on sex and contraction intensity during sustained exercise. This study examined the responses of time to task failure (TTF), performance fatigability (PF), and muscle oxygenation (SmO2) in males and females during isometric handgrip holds to failure (HTF) at 30% and 60% maximum voluntary isometric contraction (MVIC). Males (n = 12) and females (n = 12) performed a pre-MVIC, handgrip HTF at randomly ordered percentages of MVIC (either 30% or 60%), followed by a post-MVIC on the dominant arm. During the HTF testing, the TTF and SmO2 responses were recorded, and PF was determined from the pre- to post-MVICs. TTF for 30% MVIC HTF was greater than 60% MVIC HTF (p < 0.001), but was not different between males and females (p = 0.117). PF exhibited an inverse relationship with intensity for each sex, while males demonstrated greater PF than females for both 30% and 60% MVIC HTF. For the 60% MVIC HTF, males demonstrated greater desaturation than females (CI95% = [-28.1, -2.6%], p = 0.021, d = 0.621), but not for the 30% MVIC HTF (CI95% = [-12.2, 7.9%], p = 0.315, d = 0.621). Sex differences in PF and SmO2 may be attributed to the differences in muscle mass, absolute strength, contractile properties, and muscle metabolism between males and females. However, these proposed differences between males and females may not fully inform exercise performance (e.g., TTF). Sex-specific fatigue responses may be affected by complex physio-psychological mechanisms, and therefore, additional investigations under diverse exercise conditions are required to better prescribe exercise for both males and females.

Medicinal plants for the management of post-COVID-19 fatigue: A literature review on the role and mechanisms

Background

COVID-19 infection has a lasting impact on human health, which is known as post-COVID-19 conditions. Fatigue is one of the most commonly reported post-COVID-19 conditions. Management of fatigue in the post-COVID-19 era is necessary and emerging. The use of medicinal plants may provide a strategy for the management of post-COVID-19 fatigue.

Methods

A literature search has been conducted by using PubMed, Embase and Cochrane library databases is performed for studies published up to March 2024. Keywords, such as "post-COVID-19 conditions, persistent COVID-19 symptoms, chronic COVID-19, long-term sequelae, fatigue, post-COVID-19 fatigue, herbal plants, medicinal herbs, traditional Chinese medicine, pharmacological mechanisms, pharmacological actions" are thoroughly searched in Englsih and Chinese. This study reviews the pathophysiology of post-COVID-19 fatigue and potential herbal plants for managing post-COVID-19 fatigue.

Results and conclusion

Representative medicinal plants that have been extensively investigated by previous studies are presented in the study. Three common mechanisms among the most extensively studied for post-COVID-19 fatigue, with each mechanism having medicinal plants as an example. The latest clinical studies concerning the management of post-COVID-19 fatigue using medicinal plants have also been summarized. The study shows the potential for improving post-COVID-19 fatigue by consuming medicinal plants.

Time-of-day effects on physical performance and perceptual responses in Brazilian Jiu-Jitsu athletes

This study investigated how the time of day affects physical performance and perceptual responses in Brazilian Jiu-Jitsu (BJJ) athletes. Given the significance of circadian rhythms on athletic capabilities, we aimed to determine whether performance variations occur across different times of the day (morning, 10:00-11:00h; afternoon, 14:00-15:00h; and evening, 18:00-19:00h) and if these effects differ by sex. In total, 23 BJJ athletes (9 females, 14 males) participated in this study. The athletes performed physical tests including the maximal isometric handgrip strength test (HGS), Kimono Grip Strength Endurance Test (KGST), and a BJJ-specific test (BJJST) in the morning, afternoon, and evening. Perceptual responses (RPE) were also collected before the BJJST. Results showed enhanced physical performance in the evening for most tests, including increased HGS and superior performance in the KGST and BJJST for both sexes (p < 0.05). No significant differences were observed in perceptual responses (RPE) or between sexes (p > 0.05). We conclude that BJJ athletes generally perform better in the evening compared to other times of the day, with notable improvements in HSG and specific BJJ tests. The study highlights the importance of aligning training schedules with an athlete's circadian rhythm to optimize performance, leading to more efficient training sessions and improved long-term performance outcomes.

Inspiration Time: The Ultrasound Variable Necessary to Study the Diaphragm Functionality. A Cross-Sectional Controlled Study

Introduction

The diaphragm is considered the main inspiratory muscle, and as such, its assessment is crucial in patients with respiratory pathology. It is known that the contractile capacity of a muscle is determined by strength, length, and the duration of contraction. Although transdiaphragmatic pressure is the gold standard test for its study, ultrasound has been confirmed as a useful tool in clinical practice. Thanks to it, both the strength (diaphragmatic thickness) and the length of movement (diaphragmatic excursion) can be evaluated. This study aims to investigate the relationship between the inspiratory time and the diaphragmatic contraction.

Design

Cross-sectional controlled study.

Methodology

Eighty healthy subjects, yoga practitioners, with no previous respiratory pathology participated in this study. They were asked to take three different types of deep breaths: diaphragmatic with nasal inspiration, pursed-lip inspiration, and ujjayi (nasal inspiration with slight contraction of the glottis). The variables of thickness, excursion, and inspiratory contraction time were taken for each of them by ultrasound.

Results

Diaphragmatic contraction time is the only variable that shows a significant correlation with the other two. Thus, the correlation between inspiratory time and diaphragmatic thickness is significant (p < .001) for the three breaths: diaphragmatic (0.60), ujjayi (0.67), and pursed lips (0.39) and the correlation between inspiratory time and diaphragmatic excursion is significant for diaphragmatic breaths (-0.24, p = .035) and ujjayi (0.27, p = .017), but not in pursed lips (-0.01, p = .90).

Conclusion

The inspiratory contraction time and the diaphragmatic excursion are two essential variables in the dynamic functional evaluation of the diaphragm, compared to the diaphragmatic thickness measurement that only reports its strength.

Force drifts and matching errors in the lower extremities: implications for the control and perception of foot force

Accurate control of force on the environment is mechanically necessary for many tasks involving the lower extremities. We investigated drifts in the horizontal (shear) active force produced by right-footed seated subjects and the effects of force matching by the other foot. Subjects generated constant shear force at 15% and 30% of maximal voluntary contraction (MVC) using one foot. Visual feedback of shear force magnitude was provided for the first 5s, then turned off for 30s. During the 30% MVC task, we observed parallel drops in active shear and vertical force magnitudes leading to consistent drifts in the resultant force magnitude, not in its direction. Force matching by the other foot resulted in significantly lower forces when feedback was available throughout the trial. No feedback was provided for the matching foot. When the matching foot began exerting force, the task foot experienced a notable drop in all force components, with a change in force direction only for the task foot. After this initial drop, the downward drift in the task foot stopped or reversed. Subjects were unaware of these drifts and errors. Our findings suggest that shear force production involves setting a referent coordinate vector, which shows drifts and matching errors, while its direction remains stable. Involvement of the matching foot appears to perturb the neural commands to the task foot, with minor differences observed between feet. The discrepancy between the consistent force drifts and lack of awareness of the drifts indicates a difference between force perception-to-act and perception-to-report.

Analyzing the Impact of Various Jump Load Intensities on Countermovement Jump Metrics: A Comparison of Average, Peak, and Peak-to-Average Ratios in Force-Based Metrics

The purpose was to create a systematic approach for analyzing data to improve predictive models for fatigue and neuromuscular performance in volleyball, with potential applications in other sports. The study aimed to assess whether average, peak, or peak-to-average ratios of countermovement jump (CMJ) force plate metrics exhibit stronger correlations and determine which metric most effectively predicts performance. Data were obtained from nine division I female volleyball athletes over a season, recording daily jump loads (total jumps, jump counts >38.1 cm (Jumps 38+), and >50.8 cm (Jumps 50+) in height) and comparing these with CMJ force metrics recorded the next day, both average and peak. Correlations and regressions were utilized to assess the relationship and predictive value for jump loads on CMJ test data. The findings revealed that the most significant (p < 0.001 for all) negative correlations (r ranged from -0.384 to -0.529) occurred between Jumps 50+ and the average CMJ test variables. Furthermore, there were no significant relationships between jump loads and peak-to-average ratios (p ≥ 0.233). Average CMJ force metrics and Jumps 50+ provide slightly more predictive (up to 28% of variability) potential for fatigue modeling of neuromuscular performance.

Influence of an inspiratory muscle fatigue protocol on older adults on respiratory muscle strength, muscle oxygen saturation, and functional capacity: a randomized controlled trial

BACKGROUND

The fatigue of the inspiratory musculature, particularly the diaphragm, has been demonstrated to exert systemic effects on the body, impacting cardiovascular and performance outcomes. This study aimed to evaluate the influence of an inspiratory muscle fatigue protocol on respiratory muscle strength, functionality, and muscle oxygen saturation in older adults.

METHODS

A single-blinded randomized controlled clinical trial was conducted on twenty-four older adults aged over 60 years, who met inclusion criteria were physically independent in terms of gait and functionality. Participants were randomly assigned to one of three groups: control group, inspiratory muscle fatigue group, or activation group. Diaphragmatic ultrasonography (diaphragmatic thickness, thickening fraction, diaphragm movement curve), maximal inspiratory mouth pressure, muscle oxygen saturation, and functionality (timed up and go test, for five times sit to stand test) were used to measure the study variables at two time points: pre-intervention (T1) and post-intervention (T2).

RESULTS

In the maximum inspiratory pressure variable in the activation group an increase was found between baseline and post-treatment of 3.00 ± 0.93 cmH2O (P < 0.01), while in the inspiratory muscle fatigue a decrease of -6.75 ± 2.66 cmH2O (P < 0.01) was found. In addition, the inspiratory muscle fatigue group showed lower scores for respiratory and functional variables after performing the diaphragmatic fatigue intervention than the activation and control group (P < 0.05), on the other hand, the activation group showed more positive values for functional and respiratory capacity variables after performing the inspiratory muscle activation training (P < 0.05).

CONCLUSIONS

Fatigue of the inspiratory musculature appears to negatively impact inspiratory muscle strength, peripheral muscle strength, muscular oxygenation, and functionality in older adults. Activation of the inspiratory musculature could contribute to improved respiratory muscle strength and function in these individuals.

TRIAL REGISTRATION

ClinicalTrials.gov ID: NCT06266013.

Positional Differences in Jump Loads and Force and Velocity Metrics Throughout a 16-Week Division I Volleyball Season

The study quantified total and high-intensity jump counts and assessed neuromuscular performance through countermovement jump (CMJ) force and velocity metrics by position. Twelve Division I female athletes (19.6 ± 1.3 years; 182.7 ± 6.5 cm) were included in the 16-week study using wearable microsensors to monitor daily jump loads. CMJ tests were conducted twice weekly using dual force plates to measure force and velocity metrics. There were significant main effects of position (p ≤ 0.001) for jump and force plate metrics. Middle blockers accumulated significantly more jump counts of 38.1 cm or higher (jumps 38+; 65.4 ± 39.2 counts) and jump counts of 50.8 cm or higher (jumps 50+; 39.5 ± 32.7 counts) compared to outside hitters (jumps 38+; 39.4 ± 25.9 counts and jumps 50+; 15.0 ± 15.6 counts) and opposite hitters (jumps 38+; 47.9 ± 24.1 counts and jumps 50+; 29.7 ± 18.1 counts), while setters had the fewest high-intensity jump counts (jumps 38+; 19.0 ± 16.6 counts and jumps 50+; 0.4 ± 0.8 counts). Middle blockers had the highest CMJ height (36.1 ± 6.4 cm), deepest CMJ depth (-41.7 ± 6.4 cm) and peak (2.75 ± 0.22 m/s) and average (1.49 ± 0.08 m/s) propulsion velocities (2.75 ± 0.22 m/s). Meanwhile, setters had significantly greater braking RFD (7839 ± 2617 N), average (1698 ± 223 N) and peak braking force (2061 ± 248 N), and average (1446 ± 88 N) and peak propulsion force (1994 ± 213 N), compared to all other positions. Opposite and outside hitters' data fell between setters and middle blockers. Regardless of position, neuromuscular performance fluctuates during the season and there are noticeable positional differences in jump loads and force and velocity metrics.

Optimizing active recovery strategies for finger flexor fatigue

Introduction

Active recovery (AR) is used during exercise training; however, it is unclear whether the AR should involve the whole body, only the upper extremities, or only the lower extremities when aiming to maintain localized upper body performance. Therefore, this study aimed to evaluate the impact of different AR strategies on repeated intermittent finger flexor performance leading to exhaustion.

Methods

A crossover trial involving a familiarization session and three laboratory visits, each including three exhaustive intermittent isometric tests at 60% of finger flexor maximal voluntary contraction separated by 22 min of randomly assigned AR: walking, intermittent hanging, and climbing.

Results

The impulse (Nꞏs) significantly decreased from the first to third trials after walking (-18.4%, P = 0.002, d = 0.78), climbing (-29.5%, P < 0.001, d = 1.48), and hanging (-27.2%, P < 0.001, d = 1.22). In the third trial, the impulse from the intermittent test was significantly higher after walking (21,253 ± 5,650 Nꞏs) than after hanging (18,618 ± 5,174 Nꞏs, P = 0.013, d = 0.49) and after climbing (18,508 ± 4,435 Nꞏs, P = 0.009, d = 0.54).

Conclusions

The results show that easy climbing or intermittent isolated forearm contractions should not be used as AR strategies to maintain subsequent performance in comparison to walking, indicating that using the same muscle group for AR should be avoided between exhaustive isometric contractions.

Biophysics of ACL Injuries

Anterior Cruciate Ligament (ACL) injuries rank among the most prevalent and severe types of injuries, significantly impacting both athletes and non-athletes alike. These injuries not only result in immediate physical impairment, such as intense pain, substantial swelling, and a marked loss of mobility, but also carry long-term health consequences that can alter a person's quality of life. Chronic pain, persistent instability, and an increased risk of developing osteoarthritis are among the lasting effects that can follow an ACL injury. An in-depth understanding of the biophysics behind ACL injuries is paramount for devising effective prevention and treatment protocols. Biophysics, which combines principles from physics with biological systems, provides crucial insights into the mechanical and structural integrity of the ACL and its susceptibility to injury under various conditions. This systematic review aims to collate and synthesize the current knowledge surrounding the biophysical mechanisms that underlie ACL injuries.

Effects of Postural Changes Using a Standing Desk on the Craniovertebral Angle, Muscle Fatigue, Work Performance, and Discomfort in Individuals with a Forward Head Posture

Forward head posture is common among office workers who sit for long periods of time and is one of the main causes of neck pain. This study aimed to assess the effects of utilizing a standing desk on the craniovertebral angle, muscle fatigue, work performance, and discomfort in individuals with forward head posture. Twenty-four participants meeting the inclusion criteria were randomly assigned to either a traditional desk group (n = 12) or a standing desk group (n = 12). Each group engaged in 30 min of computer typing. To evaluate the impact of posture change using a standing desk, pre- and post-experiment discomfort surveys were conducted, and the craniovertebral angle and muscle fatigue were measured throughout the experiment. Work performance was assessed post-experiment based on the work completed by the participants. Intra-group analysis of the craniovertebral angle showed a significant decrease in the traditional desk group (p < 0.05) and a significant increase in the standing desk group (p < 0.05). When comparing the craniovertebral angle between the two groups, a significant difference was observed (p < 0.05). Additionally, significant differences in muscle fatigue, particularly in the levator scapulae muscles, were observed between the two groups (p < 0.05). The traditional desk group reported increased discomfort in the neck and shoulders (p < 0.05). These findings suggest that utilizing a standing desk can positively impact posture, reduce muscle fatigue, and alleviate discomfort in individuals with forward head posture, potentially serving as an intervention to prevent musculoskeletal disorders.

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.

Differential T2* changes in tibialis anterior and soleus: Influence of exercise type and perceived exertion

Understanding muscle response to exercise is critical for optimizing training strategies. This study investigated the effects of dorsiflexion and plantar flexion exercises on T2* values in the tibialis anterior (TA) and soleus (SOL) muscles and explored their relationship with muscle cross-sectional area (MCA), strength, and perceived exertion. Forty participants were divided into two exercise protocols: 30 performed dorsiflexion, 16 performed plantar flexion, and 6 completed both. T2* values were measured pre-and post-exercise using a 1.5 T MRI scanner. MCA and muscle strength were assessed via MRI and a dynamometer, while perceived exertion was measured using the Borg scale. Results showed that TA T2* values significantly increased after dorsiflexion (9.04 ± 4.21 ms), peaking 600 s post-exercise, whereas SOL T2* changes during plantar flexion were minimal (1.29 ± 1.05 ms). A significant correlation (r = 0.41, p = 0.026) was observed between T2* changes and Borg scale scores during dorsiflexion, but not with muscle strength (r = 0.08) or MCA (r = 0.35). No significant correlations were found for the SOL during plantar flexion. General linear model analysis showed a significant main effect of dorsiflexion on T2* values (p < 0.0001) and perceived exertion within the dorsiflexion protocol (p = 0.044). These findings suggest that dorsiflexion induces greater metabolic disturbances in the TA compared to plantar flexion. The results emphasize the importance of exercise-specific approaches for assessing muscle function and highlight the role of perceived exertion in evaluating muscle response.

The relationship between changes in elbow valgus laxity and forearm flexor strength during repetitive pitching

This study examined the changes in the medial elbow joint space width and forearm flexor strength due to repetitive pitching and analysed the relationships among these factors. Thirty-one collegiate baseball players pitched seven sets of 15 pitches each. The medial elbow joint space width, grip strength, and forearm flexor strengths were measured before pitching and after each set. These parameters were compared at baseline and after pitching for each set. Additionally, the relationships between changes in the medial elbow joint space and forearm flexor strength were examined for each set. The medial elbow joint space width significantly increased after four sets compared to baseline values. Compared to baseline values, grip strength decreased significantly after one set, wrist flexion and radial deviation after six, and ulnar deviation after five. However, changes in the medial joint space compared to baseline values after each set were not significantly correlated with changes in forearm flexor strength variables. Therefore, repetitive pitching causes an increase in elbow valgus laxity and a decrease in forearm flexor strength. However, the decrease in forearm muscle strength does not explain the increase in elbow valgus laxity.

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

Objective

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

Design

Pre-post within-subject repeated-measures design.

Setting

General acute care hospital and designated stroke center.

Participants

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

Interventions

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

Main Outcome Measures

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

Results

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

Conclusions

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