Improving wheelchair user sitting posture to alleviate lumbar fatigue: a study utilizing sEMG and pressure sensors.

Background: The wheelchair is a widely used rehabilitation device, which is indispensable for people with limited mobility. In the process of using a wheelchair, they often face the situation of sitting for a long time, which is easy to cause fatigue of the waist muscles of the user. Therefore, this paper hopes to provide more scientific guidance and suggestions for the daily use of wheelchairs by studying the relationship between the development of muscle fatigue and sitting posture. Methods: First, we collected surface Electromyography (sEMG) of human vertical spine muscle and analyzed it in the frequency domain. The obtained Mean Power Frequency (MPF) was used as the dependent variable. Then, the pose information of the human body, including the percentage of pressure points, span, and center of mass as independent variables, was collected by the array of thin film pressure sensors, and analyzed by a multivariate nonlinear regression model. Results: When the centroid row coordinate of the cushion pressure point is about 16(range, 7.7-16.9), the cushion pressure area percentage is about 80%(range, 70.8%-89.7%), and the cushion pressure span range is about 27(range, 25-31), the backrest pressure point centroid row coordinate is about 15(range, 9.1-18.2), the backrest pressure area percentage is about 35%(range, 11.8%-38.7%), and the backrest pressure span range is about 16(range, 9-22). At this time, the MPF value of the subjects decreased by a small percentage, and the fatigue development of the muscles was slower. In addition, the pressure area percentage at the seat cushion is a more sensitive independent variable, too large or too small pressure area percentage will easily cause lumbar muscle fatigue. Conclusion: The results show that people should sit in the middle and back of the seat cushion when riding the wheelchair, so that the Angle of the hip joint can be in a natural state, and the thigh should fully contact the seat cushion to avoid the weight of the body concentrated on the buttocks; The back should be fully in contact with the back of the wheelchair to reduce the burden on the waist, and the spine posture can be adjusted appropriately according to personal habits, but it is necessary to avoid maintaining a chest sitting position for a long time, which will cause the lumbar spine to be in an unnatural physiological Angle and easily lead to fatigue of the waist muscles.

Recognition of Human Lower Limb Motion and Muscle Fatigue Status Using a Wearable FES-sEMG System.

Functional electrical stimulation (FES) devices are widely employed for clinical treatment, rehabilitation, and sports training. However, existing FES devices are inadequate in terms of wearability and cannot recognize a user's intention to move or muscle fatigue. These issues impede the user's ability to incorporate FES devices into their daily life. In response to these issues, this paper introduces a novel wearable FES system based on customized textile electrodes. The system is driven by surface electromyography (sEMG) movement intention. A parallel structured deep learning model based on a wearable FES device is used, which enables the identification of both the type of motion and muscle fatigue status without being affected by electrical stimulation. Five subjects took part in an experiment to test the proposed system, and the results showed that our method achieved a high level of accuracy for lower limb motion recognition and muscle fatigue status detection. The preliminary results presented here prove the effectiveness of the novel wearable FES system in terms of recognizing lower limb motions and muscle fatigue status.

Fatigue and Performance Rates as Decision-Making Critera in Pacing Control During CrossFit®.

We investigated fatigue and performance rates as decision-making criteria in pacing control during CrossFit®. Thirteen male regional-level competitors completed conditions of all-out (maximum physical work from beginning to end) and controlled-split (controlled physical work in the first two rounds but maximum work in the third round) pacing throughout the Fight Gone Bad workout separated by one week. We assessed benchmarks, countermovement jumps and ratings of fatigue after each round. Benchmarks were lower in round 1 (99 vs. 114, p < .001) but higher in rounds 2 (98 vs. 80, p < .001) and 3 (97 vs. 80, p < .001) for controlled-split compared with all-out pacing. Reductions in countermovement jumps were higher after rounds 1 (-12.6% vs. 1.6%, p < .001) and 2 (-12.7% vs. -4.0%, p = .014) but similar after round 3 (-13.2% vs. -11.3%, p = .571) for all-out compared with controlled-split pacing. Ratings of fatigue were higher after rounds 1 (7 vs. 5 a.u., p < .001) and 2 (8 vs. 7 a.u, p = .023) but similar after round 3 (9 vs. 9 a.u., p = .737) for all-out compared with controlled-split pacing. During all-out pacing, countermovement jump reductions after round 2 correlated with benchmark drops across rounds 1 and 2 (r = .78, p = .002) and rounds 1 and 3 (r = -.77, p = .002) and with benchmark workout changes between pacing strategies (r = -.58, p = .036), suggesting that the larger the countermovement jump reductions the higher the benchmark drops across rounds and workouts. Therefore, benchmarks, countermovement jumps and ratings of fatigue may assess exercise-induced fatigue as decision-making criteria to improve pacing strategy during workouts performed for as many repetitions as possible.

Effects of photobiomodulation therapy on muscle function in individuals with multiple sclerosis.

BACKGROUND: In people with multiple sclerosis (pwMS), muscle fatigue and weakness are common issues that can interfere with daily activities. Photobiomodulation therapy (PBMT), comprising light in a 600-1100 nm bandwidth, is a low-level laser therapy thought to improve muscle performance in non-disease populations, in part, by improving mitochondrial function and thus, might be beneficial in pwMS. Given this potential, we aimed to investigate the effects of PBMT on muscle performance in pwMS, both in the short-term and over an extended period. METHODS: This study consisted of two parts with a randomized double-blind crossover design. In study I, muscle function was assessed in four sessions before and after PBMT in ambulatory pwMS (N = 17, F = 14) as follows: maximal voluntary contraction (MVC) and muscle fatigue of the right tibialis anterior (TA) muscle was compared at baseline and following a two-min submaximal fatiguing contraction. Then, PBMT was administered to the belly of TA muscle at different doses of energy of an active device (40 J, 80 J, 120 J) or placebo. The muscle function assessment was then repeated. OUTCOME VARIABLES: muscle force recovery (%), muscle fatigue (%). Statistical tests included McNemar's exact test, Wilcoxon signed-rank test, and the Friedman test. In study II, a subgroup from study I (N = 12, F = 11) received individualized doses (i.e., best dose-effect observed in study I) of active, or placebo PBMT, which was administered on the TA muscle for two weeks. Muscle function assessments were performed pre- and post-PBMT in four sessions similar to study I. OUTCOME VARIABLES: Baseline strength (N), endurance time (s), and muscle fatigue (%). The Wilcoxon signed-rank test was used for statistical analysis. Values are reported as mean (SD). RESULTS: In study I, participants who received a high dose of PBMT showed significant improvement in force recovery (101.89 % (13.55 %)) compared to the placebo group (96.3 % (18.48 %); p = 0.03). Muscle fatigue did not significantly improve with either active PBMT or placebo. In study II, active PBMT resulted in a significant improvement in muscle strength compared to both the baseline (pre-PBMT = 162.70 N (37.52 N); post-PBMT = 185.56 N (33.95 N); p = 0.01) and the placebo group (active PBMT: mean-change = 22.87 N (23.67 N); placebo: mean-change = -4.12 N (31.95 N); p = 0.02). Endurance time and muscle fatigue did not show significant improvement with either active PBMT or placebo. CONCLUSION: Our findings suggest that an individualized dose of PBMT might improve muscle performance, including force recovery and strength in individuals with mild-moderate MS. Therefore, PBMT might be a novel therapeutic modality, either as a standalone treatment or in combination with other interventions, to improve muscle performance in pwMS.

Effects of Limosilactobacillus reuteri ID-D01 Probiotic Supplementation on Exercise Performance and Gut Microbiota in Sprague-Dawley Rats.

The gut microbiota composition in animals and humans has recently been found to be influenced by exercise. Although Limosilactobacillus reuteri strains have notable probiotic properties that promote human health, understanding of its effects in combination with exercise and physical activity is limited. Therefore, this study examined the effects of L. reuteri ID-D01, a human-derived probiotic, on exercise performance and fatigue in Sprague-Dawley rats. Organ weight, maximal running distance, serum biochemistry, muscle performance, microbial community composition, and short-chain fatty acid (SCFA) levels were assessed. Results indicated that ID-D01 supplementation significantly improved endurance performance. Rats in the probiotic group demonstrated a significant increase in maximal running distance compared with that in the control group (p < 0.05). Additionally, levels of fatigue markers, such as lactate and creatine phosphokinase, were significantly reduced in the ID-D01-administered groups, suggesting its potential to alleviate exercise-induced fatigue. Microbiome analysis revealed a distinct shift in gut microbiota composition in response to ID-D01 administration. The group that received ID-D01 probiotics exhibited a significant increase in the abundance of SCFA-producing bacteria, particularly Akkermansia spp., compared with that in the control groups. Furthermore, they showed elevated production of SCFAs, such as acetate and butyrate. In conclusion, this study demonstrated that ID-D01 can enhance exercise performance and reduce fatigue. Herein, we highlighted that human-derived probiotics could improve physical performance, as observed by changes in gut microbiota composition and SCFA production.

Quantitative assessment of muscle activity of back and lower extremities, whole body sagittal alignment, body sway, and health-related quality of life in adult spinal deformity patients before and after spinopelvic correction surgery: From the standpoint of the "cone of economy".

BACKGROUND AND AIMS: Pain and muscle fatigue in the low back and lower extremity associated with adult spinal deformity (ASD) markedly limit daily activities and affect quality of life. This study aimed to clarify if spinal correction surgery decreases the muscle activity requirements in relation to alignment and balance parameters. METHODS: Integrated electromyogram (I-EMG) studies of the low back and lower extremity in addition to whole body alignment, body sway, and health-related quality of life (HRQOL) were evaluated in 16 patients with ASD before and after surgery. Sixteen healthy volunteers were included as control subjects. Muscle activities of the bilateral lumbar paravertebral, biceps femoris, rectus femoris, gastrocnemius, and tibialis anterior were measured using surface electromyogram in both resting and working standing positions. Surgical outcomes were based on improvements in muscle fatigue using the sum of the whole muscle I-EMGs and body sway. HRQOL was evaluated by SRS-22r, which measures 4 domains (function, pain, self-image, mental health) and subtotal scores. RESULTS: In controls, the sum of the 10 whole I-EMGs (mVms; mean ± SD) was 3316 ± 1247 in the resting standing position and 5625 ± 2065 in the working standing position. The I-EMG values were higher in ASD patients than in healthy subjects; in the resting standing position, the sum of the whole 10 I-EMGs significantly decreased from baseline (9125 ± 3529) to 3 (6088 ± 1793) and 6 (6381 ± 1776) months postoperatively (p < 0.01). In the working standing position, the sum in ASD patients also significantly decreased from baseline (14,160 ± 5474) to 3 (8085 ± 2540) and 6 (8557 ± 3025) months postoperatively (p < 0.01). I-EMG values did not differ significantly between the 3- and 6-month time points in either condition. Body sway was also improved postoperatively at 3 months and maintained at 6 months along with the amelioration of whole-body sagittal alignment, and 4 domains and subtotal SRS-22r scores significantly increased postoperatively. CONCLUSION: Following spinopelvic correction surgery, whole body sagittal alignment was improved, and muscle activity based on I-EMG and body sway were significantly decreased. The SRS-22r scores after surgery also indicated significant improvement, suggesting that muscle fatigue in the standing position was ameliorated, i.e., the "cone of economy" was normalized.

The influence of low resistance respiratory muscle training on pulmonary function and high intensity exercise performance.

Background/objectives: Respiratory muscle training (RMT) was recognized as an effective means to improve respiratory muscle (RM) strength and enhance exercise performance. The purpose of this study was to examine the effect of low-intensity RMT on RM strength, pulmonary function, and performance. Methods: Fourteen healthy active adults were assigned randomly to either a training or placebo group. The training group completed six weeks of RMT, which consisted of a first week, 1 set of 15 min/d, 5 d/wk at 10-25% of maximal inspiratory pressure (PImax), and the remaining 5 weeks, 2 sets of 15 min/d, 5 d/wk, at 30% PImax. The placebo group followed the same protocol but with almost no additional ventilatory resistance. Measurement of RM strength and endurance, spirometry, and endurance exercise performance were obtained before and after the RMT program. Results: In the training group, PImax (+14%) and maximal expiratory pressure (PEmax, +27%), forced vital capacity (FVC, +3.6%), maximal oxygen uptake (VO2max, +11%), and time to exhaustion (Tlim90%, +25%) increased significantly from baseline values (P < 0.05). No significant changes were observed in the placebo group. Also, no significant interaction in maximum voluntary ventilation (MVV12), minute ventilation (VE), and respiratory rate (RR) were detected. Conclusions: These data suggest that low-intensity RMT is an effective tool to improve RM strength, pulmonary elastic properties and endurance exercise performance.

Four-compartment muscle fatigue model to predict metabolic inhibition and long-lasting nonmetabolic components.

Introduction: Computational muscle force models aim to mathematically represent the mechanics of movement and the factors influencing force generation. These tools allow the prediction of the nonlinear and task-related muscle behavior, aiding biomechanics, sports science, and rehabilitation. Despite often overlooking muscle fatigue in low-force scenarios, these simulations are crucial for high-intensity activities where fatigue and force loss play a significant role. Applications include functional electrical stimulation, motor control, and ergonomic considerations in diverse contexts, encompassing rehabilitation and the prevention of injuries in sports and workplaces. Methods: In this work, the authors enhance the pre-existing 3CCr muscle fatigue model by introducing an additional component of force decay associated with central fatigue and a long-term fatigue state. The innovative four-compartment model distinguishes between the short-term fatigued state (related to metabolic inhibition) and the long-term fatigued state (emulating central fatigue and potential microtraumas). Results: Its validation process involved experimental measurements during both short- and long-duration exercises, shedding light on the limitations of the traditional 3CCr in addressing dynamic force profiles.

Immediate effect of kinesiology taping on muscle strength, static balance and proprioception after eccentric muscle fatigue on ankle: a randomized cross-over trial.

BACKGROUND: Kinesiology Taping(KT) is commonly used as a physical therapy to prevent exercise-induced fatigue. This study aims to evaluate the immediate effects of KT on muscle strength, static balance, and proprioception after eccentric muscle fatigue on ankle. METHODS: Twenty healthy male university students were recruited. The experimental protocol was structured into four sessions, each separated by a one-week washout period to prevent carryover effects. Participants were randomly allocated to one of four intervention conditions in each session, ensuring no participant received the same intervention twice. These conditions were: no taping(NT),sham taping(ST),athletic taping(AT),and kinesiology taping(KT).Taping was applied immediately following an eccentric muscle fatigue protocol targeting the ankle, and assessments were conducted in the order of proprioception, muscle strength and static balance. Isometric muscle strength and proprioception were evaluated using the Biodex isokinetic system. Static balance was measured using the TecnoBody balance platform. RESULTS: KT had a significantly higher plantarflexion/dorsiflexion peak torque, dorsiflexion average peak torque, and plantarflexion/dorsiflexion average power at 60°/s compared with NT and ST in terms of isometric muscle strength (p < 0.05).Furthermore, the plantarflexion peak torque of KT was significantly greater than AT at 60°/s[p = 0.005,95% confidence interval(CI) = 3.39 to 18.20] and 180°/s[p = 0.006,95%CI(2.62,21.98)]. In terms of proprioception, KT showed a lower absolute error in 25° plantarflexion and 10° dorsiflexion compared to NT, ST and AT. For static balance with eyes-open and eyes-closed conditions, AT and KT had a lower total sway area than NT and ST (p < 0.05). Additionally, a significant difference in total sway length with eyes-open condition was observed between AT and KT[p < 0.001,95%CI(-431.81,-168.25)];total sway area and the center of pressure(COP) velocity in the mediolateral(ML) and anteroposterior(AP) directions with eyes-closed condition were significantly lower in AT compared to KT. CONCLUSION: This study suggests that KT is more effective than other taping conditions in improving muscle strength and proprioception after eccentric muscle fatigue on ankle. However, AT is more helpful in increasing static postural control ability after ankle muscle fatigue than KT. TRIAL REGISTRATION: This study was registered with www.chictr.org.cn (registration number: ChiCTR2300068278) on 13/2/2023.

Assessment of Muscle Stiffness Using the MyotonPro: Effects of Fatigue on Vastus Lateralis and Medialis Muscles.

BACKGROUND: The investigation of soft tissue stiffness has garnered increasing interest due to its potential applications in detecting tissue conditions, monitoring therapy effects, and preventing sports injuries. This study utilized the MyotonPro as a reliable measurement device to assess muscle stiffness and muscle frequency in the vastus lateralis and medialis muscles of both the dominant and non-dominant legs. METHODS: Sixteen young, healthy subjects (seven males and nine females, age 25 ± 3.46 years) participated in this study. To induce maximal muscle fatigue, the vastus lateralis and vastus medialis muscles were subjected to a 30 kg load using a single-leg leg press. Pre- and post-fatigue measurements were conducted by two testers on the dominant and non-dominant legs, respectively, employing the MyotonPro. RESULTS: We revealed a significant increase in muscle stiffness after maximal muscle fatigue. Specifically, on the dominant side, the vastus lateralis exhibited a stiffness increase of 6.5%, while the vastus medialis showed a 6.3% increase. On the non-dominant side, the vastus lateralis demonstrated a 7.6% increase, and the vastus medialis exhibited a 6.7% increase in muscle stiffness. Furthermore, muscle frequency increased by 8.6% (vastus lateralis) and 13.5% (vastus medialis) on the dominant side and by 15.1% (vastus lateralis) and 6.3% (vastus medialis) on the non-dominant side. The reliability of the measurements varied, with Cronbach's alpha values ranging from inadequate 0.49 to very good 0.88. CONCLUSION: This study affirms the efficacy of the MyotonPro as a measurement device for assessing muscle stiffness and establishes its reliability. The observed increase in muscle stiffness after maximal muscle fatigue, accompanied by changes in muscle frequency, underscores the device's utility. However, further research is warranted to validate the reproducibility of these findings and explore additional facets of the muscular response to fatigue.

Passive heating-induced changes in muscle contractile function are not further augmented by prolonged exposure in young males experiencing moderate thermal stress.

Background: We investigated the impact of 1) passive heating (PH) induced by single and intermittent/prolonged hot-water immersion (HWI) and 2) the duration of PH, on muscle contractile function under the unfatigued state, and during the development of muscle fatigue. Methods: Twelve young males volunteered for this study consisting of two phases: single phase (SP) followed by intermittent/prolonged phase (IPP), with both phases including two conditions (i.e., four trials in total) performed randomly: control passive sitting (CON) and HWI (44-45°C; water up to the waist level). SP-HWI included one continuous 45-min bath (from 15 to 60 min). IPP-HWI included an initial 45-min bath (from 15 to 60 min) followed by eight additional 15-min baths interspaced with 15-min breaks at room temperature between 75 and 300 min. Intramuscular (Tmu; measured in the vastus lateralis muscle) and rectal (Trec) temperatures were determined. Neuromuscular testing (performed in the knee extensors and flexors) was performed at baseline and 60 min later during SP, and at baseline, 60, 90, 150 and 300 min after baseline during IPP. A fatiguing protocol (100 electrical stimulations of the knee extensors) was performed after the last neuromuscular testing of each trial. Results: HWI increased Tmu and Trec to 38°C-38.5°C (p < 0.05) during both SP and IPP. Under the unfatigued state, HWI did not affect electrically induced torques at 20 Hz (P20) and 100 Hz (P100). However, it induced a shift towards a faster contractile profile during both SP and IPP, as evidenced by a decreased P20/P100 ratio (p < 0.05) and an improved muscle relaxation (i.e., reduced half-relaxation time and increased rate of torque relaxation; p < 0.05). Despite a reduced voluntary activation (i.e., -2.63% ± 4.19% after SP-HWI and -5.73% ± 4.31% after IPP-HWI; condition effect: p < 0.001), HWI did not impair maximal isokinetic and isometric contraction torques. During the fatiguing protocol, fatigue index and the changes in muscle contractile properties were larger after HWI than CON conditions (p < 0.05). Finally, none of these parameters were significantly affected by the heating duration. Conclusion: PH induces changes in muscle contractile function which are not augmented by prolonged exposure when thermal stress is moderate.

Relationship between maximal oxygen uptake, within-set fatigue and between-set recovery during resistance exercise in resistance-trained men and women.

BACKGROUND: The primary aim of this study was to examine the relationship between maximal oxygen update (V̇O2max) and within-set fatigue and between-set recovery during resistance exercise in men and women. METHODS: We examined the relationship between V̇O2max and various indices of fatigue and recovery during parallel squats (3 sets, 90 s rest, 70% of 1RM to failure) and isokinetic knee extensions (3 × 10 maximal repetitions at 60 deg/s, 45 s rest) in 28 (age 27.0 ± 3.6 years) resistance-trained subjects (14 men and 14 women). We also examined whether there were sex differences in within-set fatigue and between-set recovery. RESULTS: V̇O2max was weakly related to recovery and fatigue in both men and women (range of P-values for V̇O2max as a covariate; 0.312-0.998, range of R-values, 0.005-0.604). There were no differences between the sexes in fatigue within a set for the squat, but men showed less within-set fatigue than women in the first set of the isokinetic knee extension exercise (~ 8% torque loss difference, main effect of sex P = 0.034). Regarding recovery between sets, men showed greater relative peak power (P = 0.016) and peak torque (P = 0.034) loss between sets in both exercises, respectively, compared to women. Women also tended to complete more repetitions than men (main effect of sex, P = 0.057). Loss of peak torque between sets in knee extension was evident in both absolute and relative (%) values in men but not in women. CONCLUSIONS: Our study suggests that aerobic capacity is weakly associated with within-set fatigue and between-set recovery in resistance training in both men and women. Women and men show comparable levels of within-set fatigue in the multi-joint squat, but women show more within-set fatigue during the single-joint isokinetic knee extension compared with men. In contrast, women recover better than men between sets in both exercises.

Myoelectric, Myo-Oxygenation, and Myotonometry Changes during Robot-Assisted Bilateral Arm Exercises with Varying Resistances.

Robot-assisted bilateral arm training has demonstrated its effectiveness in improving motor function in individuals post-stroke, showing significant enhancements with increased repetitions. However, prolonged training sessions may lead to both mental and muscle fatigue. We conducted two types of robot-assisted bimanual wrist exercises on 16 healthy adults, separated by one week: long-duration, low-resistance workouts and short-duration, high-resistance exercises. Various measures, including surface electromyograms, near-infrared spectroscopy, heart rate, and the Borg Rating of Perceived Exertion scale, were employed to assess fatigue levels and the impacts of exercise intensity. High-resistance exercise resulted in a more pronounced decline in electromyogram median frequency and recruited a greater amount of hemoglobin, indicating increased muscle fatigue and a higher metabolic demand to cope with the intensified workload. Additionally, high-resistance exercise led to increased sympathetic activation and a greater sense of exertion. Conversely, engaging in low-resistance exercises proved beneficial for reducing post-exercise muscle stiffness and enhancing muscle elasticity. Choosing a low-resistance setting for robot-assisted wrist movements offers advantages by alleviating mental and physiological loads. The reduced training intensity can be further optimized by enabling extended exercise periods while maintaining an approximate dosage compared to high-resistance exercises.

Edward F. Adolph Distinguished Lecture. Age and sex differences in the limits of human performance: fatigability and real-world data.

High-level athletic performances may be a proxy for the trajectory of optimal function of human biology with advanced aging and the differences between males and females. Males are faster, stronger, and more powerful than females and these physical attributes decline dramatically with advanced aging for both sexes. Experimental mechanistic studies determine the physiological mechanisms for these sex and age differences in human physical performance. The assumption however, that real-world performances solely reflect the biological and physiological differences between the sexes and with advanced aging, even among elite athletes, is not complete. This review presents evidence that an integrated approach encompassing analysis of real-world data and experimental mechanistic studies is necessary to determine the biological and sociocultural factors attributed to the limits of performance with aging and between males and females. First, experimental studies are presented that focus on the sex and age differences in performance fatigability that determine the physiological mechanisms of absolute and relative exercise performance. Second, analysis of current and historical real-world data including world records, and performances of elite, collegiate, and competitive age-group athletes are highlighted. These data illustrate that the upper limits of physical performance that have changed historically, and other factors such as sociocultural influences, explain the widening of the sex and age gaps in human performance observed in real-world data even in present-day performances. These approaches have broader significance when applied to understanding the impact of the historically low representation of females and minority groups in biomedical research on health outcomes.

Electromyography-driven musculoskeletal models with time-varying fatigue dynamics improve lumbosacral joint moments during lifting.

Muscle fatigue is prevalent across different aspects of daily life. Tracking muscle fatigue is useful to understand muscle overuse and possible risk of injury leading to musculoskeletal disorders. Current fatigue models are not suitable for real-world settings as they are either validated using simulations or non-functional tasks. Moreover, models that capture the changes to muscle activity due to fatigue either assume a linear relationship between muscle activity and muscle force or utilize a simple muscle model. Personalised electromygraphy (EMG)-driven musculoskeletal models (pEMS) offer person-specific approaches to model muscle and joint kinetics during a wide repertoire of daily life tasks. These models utilize EMG, thus capturing central fatigue-dependent changes in multi-muscle bio-electrical activity. However, the peripheral muscle force decay is missing in these models. Thus, we studied the influence of fatigue on a large scale pEMS of the trunk. Eleven healthy participants performed functional asymmetric lifting task. Average peak body-weight normalized lumbosacral moments (BW-LM) were estimated to be 2.55 ± 0.26 Nm/kg by reference inverse dynamics. After complete exhaustion of the lower back, the pEMS overestimated the peak BW-LM by 0.64 ± 0.37 Nm/kg. Then, we developed a time-varying muscle force decay model resulting in a time-varying pEMS (t-pEMS). This reduced the difference between BW-LM estimated by the t-pEMS and reference to 0.49 ± 0.14 Nm/kg. We also showed that five fatiguing contractions are sufficient to calibrate the t-pEMS. Thus, this study presents a person and muscle specific model to track fatigue during functional tasks.

A new fractional fuzzy dispersion entropy and its application in muscle fatigue detection.

Recently, fuzzy dispersion entropy (DispEn) has attracted much attention as a new nonlinear dynamics method that combines the advantages of both DispEn and fuzzy entropy. However, it suffers from limitation of insensitivity to dynamic changes. To solve this limitation, we proposed fractional fuzzy dispersion entropy (FFDispEn) based on DispEn, a novel fuzzy membership function and fractional calculus. The fuzzy membership function was defined based on the Euclidean distance between the embedding vector and dispersion pattern. Simulated signals generated by the one-dimensional (1D) logistic map were used to test the sensitivity of the proposed method to dynamic changes. Moreover, 29 subjects were recruited for an upper limb muscle fatigue experiment, during which surface electromyography (sEMG) signals of the biceps brachii muscle were recorded. Both simulated signals and sEMG signals were processed using a sliding window approach. Sample entropy (SampEn), DispEn and FFDispEn were separately used to calculate the complexity of each frame. The sensitivity of different algorithms to the muscle fatigue process was analyzed using fitting parameters through linear fitting of the complexity of each frame signal. The results showed that for simulated signals, the larger the fractional order q, the higher the sensitivity to dynamic changes. Moreover, DispEn performed poorly in the sensitivity to dynamic changes compared with FFDispEn. As for muscle fatigue detection, the FFDispEn value showed a clear declining tendency with a mean slope of -1.658 × 10-3 as muscle fatigue progresses; additionally, it was more sensitive to muscle fatigue compared with SampEn (slope: -0.4156 × 10-3) and DispEn (slope: -0.1675 × 10-3). The highest accuracy of 97.5% was achieved with the FFDispEn and support vector machine (SVM). This study provided a new useful nonlinear dynamic indicator for sEMG signal processing and muscle fatigue analysis. The proposed method may be useful for physiological and biomedical signal analysis.

Effects of a Passive Back-Support Exosuit on Postural Control and Cognitive Performance During a Fatigue-Inducing Posture Maintenance Task.

OBJECTIVE: To evaluate the effectiveness of passive back-support exosuit on postural control and cognitive performance during a fatigue-inducing posture maintenance task. BACKGROUND: Wearable support systems (exoskeletons/exosuits) reduce physical demands but may also influence postural control and cognitive performance by reducing muscular fatigue. METHOD: Eighteen participants visited on two different days to test an exosuit system and performed dual-task cognitive assessments based on human information processing (information acquisition, information integration, and action implementation) while maintaining a 35° trunk flexion posture for 16 minutes. Center-of-pressure (CoP), cognitive performance, and perceived workload were recorded, while erector spinae muscle activity was captured to quantify muscle fatigue. RESULTS: The exosuit was effective in reducing erector spinae muscle fatigue during the static posture maintenance task (61% less in Δmedian frequency: -9.5 Hz (EXO-Off) versus -3.7 Hz (EXO-On)). The fatigue-inducing task increased CoP velocity as a function of time (29% greater: 9.3 mm/sec (pre) versus 12.0 mm/sec (post)), and exosuit use decreased CoP velocity (23% less: 12.1 mm/sec (EXO-Off) versus 9.4 mm/sec (EXO-On)). The exosuit was also effective at mitigating cognitive degradation, as evidenced by a higher hit-to-signal ratio (8% greater: 81.3 (EXO-Off) versus 87.9 (EXO-On)) in the information integration task and reducing perceived workload in all stages of human information processing. CONCLUSION: Exosuit provided benefits of postural control and information integration processing during a 16-min static posture maintenance task. APPLICATION: Torso exoskeletons/suits can have positive implications for occupations with concurrent physical and cognitive demands.

Acute Effect of Oral Adenosine Triphosphate (ATP) Supplementation on Muscular Performance in Trained Adults.

INTRODUCTION: Adenosine Triphosphate is a molecule with the function of generating energy, where high levels are directly related to cellular and muscular health. Oral supplementation appears as a possibility to guarantee such levels, and is normally consumed in capsules, which can be acute or chronic. OBJECTIVES: To verify the influence of a dose of ATP on muscular performance in adults. METHODS: This is an acute, crossover, randomized, double-blind, placebo-controlled intervention study. 18 trained men were recruited, with an average age of 27.95 years. Two visits were made to the laboratory, where each of the protocols consisted of randomized supplementation of 400 mg of Peak ATP® or placebo, and 30 min later, five series were performed, where the first consisted of five repetitions and the following four of ten repetitions at 60° per second in knee extension and flexion on a Biodex® 4.0 isokinetic dynamometer, where the volunteers' muscle strength and resistance to fatigue were measured. For data analysis, data normality was assessed using Shapiro Wilk, the ANOVA repeated measures test with Bonferroni post hoc. To identify the size of the effect, the Cohen test was performed, and the statistical package used was SPSS 25 with an applied significance of p < 0.05. RESULTS: Acute supplementation was unable to achieve significant improvements in muscle strength indicators. The supplement delays drops in strength as the exercise progresses in knee extension compared to the placebo. CONCLUSIONS: An acute dose of 400 mg of ATP did not improve the volunteers' muscle strength indicators, but it was able to reduce fatigue levels as the exercise progressed, enabling greater performance for longer.