Muscle Fatigue

Purpose-To examine the effect of a high-intensity concurrent training program utilizing a single gravity-independent device on maintaining skeletal muscle function and aerobic capacity during short-term unilateral lower limb suspension (ULLS). Methods-Nineteen subjects (10 male; 9 female; 21.0 ± 2.5 yr, 65.4 ± 12.2 kg) were separated into 2 groups: 1) 10 day unilateral lower limb suspension only (ULLS; n = 9) and 2) 10 day ULLS plus aerobic and resistance training (ULLS+EX; n = 10). Exercise was performed on a single gravity-independent Multi-Mode Exercise Device (M-MED) with alternating days of highintensity interval aerobic training and maximal exertion resistance training. Results-Aerobic capacity increased by 7% in ULLS+EX (P < 0.05). Knee extensor and ankle plantar flexor three repetition max increased in the ULLS+EX group (P < 0.05) but this change was only different than ULLS in the plantar flexors (P < 0.05). Peak torque levels decreased with ULLS but were increased for the knee extensors and attenuated for the ankle plantar flexors with ULLS+EX (P < 0.05). A shift towards type IIx myosin heavy chain mRNA occurred with ULLS and was reversed with ULLS+EX in the vastus lateralis (P < 0.05) but not the soleus. Myostatin and atrogin increased with ULLS in both the vastus lateralis and soleus but this change was mitigated with ULLS+EX only in the vastus lateralis (P = 0.0551 for myostatin; P < 0.05 for atrogin). Citrate synthase was decreased in the soleus during ULLS but was increased with ULLS +EX (P < 0.05). indicate that an M-MED class countermeasure device appears to be effective at mitigating the deconditioning effects of microgravity simulated during a modified-ULLS protocol.

To test the hypothesis that muscle O2 uptake (V˙o 2) on-kinetics is limited, at least in part, by peripheral O2 diffusion, we determined theV˙o 2 on-kinetics in 1) normoxia (Control); 2) hyperoxic gas breathing (Hyperoxia); and 3) hyperoxia and the administration of a drug (RSR-13, Allos Therapeutics), which right-shifts the Hb-O2dissociation curve (Hyperoxia+RSR-13). The study was conducted in isolated canine gastrocnemius muscles ( n = 5) during transitions from rest to 3 min of electrically stimulated isometric tetanic contractions (200-ms trains, 50 Hz; 1 contraction/2 s; 60–70% peakV˙o 2). In all conditions, before and during contractions, muscle was pump perfused with constantly elevated blood flow (Q˙), at a level measured at steady state during contractions in preliminary trials with spontaneous Q˙. Adenosine was infused intra-arterially to prevent inordinate pressure increases with the elevated Q˙. Q˙ was measured continuously, arterial and popliteal venous O2 concentration...

and other authors have proposed that central motor command (CMC) and, consequently, exercise performance in hypoxia is determined by the following. 1) By simple negative feedback (1, 2) or complex feedback/ feedforward (4) subconscious homeostatic control systems that, based on afferent information from central and peripheral chemoreceptors, limit skeletal muscle recruitment to avoid dangerous brain deoxygenation (4), respiratory failure (2), or excessive locomotor muscle fatigue and pain (1), or 2) by the direct negative effects of severe brain hypoxia on maximal voluntary CMC and/or motivation to exercise (1, 6). However, these authors have overlooked a third possibility, which, in our opinion, is simpler and biologically more plausible. Indeed, it is well established that the sensation of respiratory effort increases when ventilation is reflexly stimulated by hypoxia. According to our psychobiological model of exercise performance based on Brehm's motivational intensity theory (3), this perceptual effect of hypoxia can increase overall perceived exertion and cause subjects to disengage from a task (which, in physiological terms, means a sudden reduction in CMC and exhaustion) earlier than in normoxic conditions even assuming no effect of hypoxia on motivation to exercise. During time trials, subjects are able to compensate for the increased sensation of respiratory effort by voluntarily reduce power output. This behavioral strategy maintains overall perception exertion within normal limits to ensure successful completion of the time trial despite hypoxia. Future studies need to control for rival hypotheses and establish experimentally which of the above three models is the most valid explanation for reduced CMC and exercise performance in hypoxia.

The aim of this study was to evaluate tile layers workload at a construction site and its influence to their working ability. The subjects (n = 8) were male tile layers (mean ± SE) age of 36 ± 3.6 years. First the subjects completed a questionnaire and thereafter they performed before and after the working day a test of tile setting on a special wall, where was 3 stages and every stage they must set correctly 14 tiles. In the course of test the electromyographical (EMG) power spectral median frequency (MF) of biceps brachii, trapezius, deltoideus and erector spinae muscles was measured (both sides). The results of questionnaire indicate that the tile layer's most burdened parts of the body were knees, lower back and upper back. Workers complained most about tiredness, skin irritations, dyscomfort in eyes, knee, leg, lower back and neck/shoulder pain. It is important emphasis that all tile layers were taking tiles from a left side. Objectively estimated muscle fatigue emerged before and after the working day when comparing EMG power spectral MF measured at the beginning and end of the tile setting test. The results indicated that the most burdened muscle was right erector spinae for all 3 stages. In case of physical work, it is advisable to make short breaks every hour, so as to avoid the problems caused by overload. The results of this study can be used by specialists of ergonomics and production managers.

Introduction: Neuromuscular electrical stimulation (NMES) is used by physical therapists in the clinic. The efficacy of NMES is limited by the rapid onset muscle fatigue. The role of NMES parameters is muscle fatigue is not clear. Objective: To determine the effects of shape waveform on muscle fatigue, during NMES. Methods: Twelve healthy subjects participated in the study. Subjects were assigned to 1 of 3 groups, randomly. Group assignment determined the order in which they were tested using 3 different shape waveforms. Maximal voluntary isometric contraction (MVIC) was measured during the first session. Fatigue test was applied with amplitude required to elicit 50% of the MVIC. In each 3 testing sessions torque of contraction and level comfort were measured, and percent fatigue was calculated. Analysis of variance tests for dependent samples was used to determine the effect of shape waveform on muscle fatigue and comfort scores Results: The results showed no one shape waveform was most fatigable and that SQ wave induced more uncomfortable stimulus.

Objectives: There are two sub systems of paraspinal muscles, the global-mobilizing system and the local stabilizing system. The multifidus muscles are assigned to the local system and stabilize the joints. In contrast, the longissimus muscles are assigned to the global system and force exertion. This study aimed to investigate the median frequency changes in mobilizing and stabilizing muscles following fatigue. Method: A cross sectional study was designed. sEMG measurements were recorded from twenty participants following a fatigue protocol in B200 dynamometer. Participants performed dynamic trunk fl exion-extension against a moderate resistance while standing in a static dynamometer until they could no longer performs the task because of fatigue. Results: Statistical analyses showed significant differences between median frequencies pre and post fatigue (p<0.05). Median frequency of the right and left multifudus muscles reduced from "99.12 and 93.2" to "86.55 and 85.85" respectively. Also Median frequency of the right and left longissimus reduced from "76. 54 and 76.82" to "66.43 and 68.55" respectively. Conclusion: Median frequency shift toward low values following fatigue in global and local paraspinal muscles was seen. However, median frequency values for the local stabilizer muscle were higher than median frequency values for the global muscles.

Background and Aim: Proprioception is one of the most precise and delicate senses of the human body. It plays an important role in coordination and postural control by protecting the body against trauma and accidents. Although many studies have assessed the effect of fatigue on proprioception in the limbs and the low back region, but a few studies have investigated its possible effect on the cervical region. Material and Methods: Seventeen (8 women, 9 men) young and healthy volunteers were asked to perform the Cervicocephalic Relocation Test (CRT) to the neutral head position by relocating the head on trunk after actively rotating the head to right and left sides, in two conditions; before and after muscular fatigue. Absolute, constant and variable errors were used to evaluate cervical joint repositioning accuracy. Results: Fatigue had no effect on cervical joint position sense, Furthermore no considerable difference was seen between male and female subjects (p>0.05). The results suggest that following isometric fatigue of upper trapezuis muscles, no change is produced in the repositioning accuracy of both sexes. Furthermore, sex had no effect on cervical joint proprioception.

A 49-year-old man with chronic obstructive pulmonary disease (COPD) presented with significant tachypnoea, fevers, productive cough and increased work of breathing for the previous 4 days. Laboratory data showed elevated lactate of 3.2 mEq/L. Continuous inhaled ipratropium and albuterol nebuliser treatments were administered. Lactate levels increased to 5.5 and 3.9 mEq/L, at 6 and 12 h, respectively. No infectious source was found and the lactic acidosis cleared as the patient improved. The lactic acidosis was determined to be secondary to respiratory muscle fatigue and inhaled β-agonist therapy, two under-recognised causes of lactic acidosis in patients presenting with respiratory distress. Lactic acidosis is commonly used as a clinical marker for sepsis and shock, but in the absence of tissue hypoperfusion and severe hypoxia, alternative aetiologies for elevated levels should be sought to avoid unnecessary and potentially harmful medical interventions.

Symptoms guide disease management, and patients frequently report HIV-related symptoms, but HIV symptom patterns reported by patients have not been described in the era of improved antiretroviral treatment. The objectives of our study were to investigate the prevalence and burden of symptoms in people living with HIV and attending an outpatient clinic. The prevalence, burden, and bothersomeness of symptoms reported by patients in routine clinic visits during 2011 were assessed using the 20-item HIV Symptom Index. Principal component analysis was used to identify symptom clusters and relationships between groups using appropriate statistic techniques. Two main clusters were identified. The most prevalent and bothersome symptoms were muscle aches/joint pain, fatigue, and poor sleep. A third of patients had seven or more symptoms, including the most burdensome symptoms. Even with improved antiretroviral drug side-effect profiles, symptom prevalence and burden, independent of HIV viral ...

Electrical muscle stimulation demonstrates potential for preventing muscle atrophy and for restoring functional movement after spinal cord injury (SCI). Control systems used to optimize delivery of electrical stimulation protocols depend upon the algorithms generated using computational models of paralyzed muscle force output. The Hill-Huxley-type model, while being highly accurate, is also very complex, making it difficult for real-time implementation. In this paper, we propose a Wiener-Hammerstein system to model the paralyzed skeletal muscle under electrical stimulus conditions. The proposed model has substantial advantages in identification algorithm analysis and implementation including computational complexity and convergence, which enable it to be used in real-time model implementation. Experimental data sets from the soleus muscles of fourteen subjects with SCI were collected and tested. The simulation results show that the proposed model outperforms the Hill-Huxley-type model not only in peak force prediction, but also in fitting performance for force output of each individual stimulation train.

Over the past century, understanding the mechanisms underlying muscle fatigue and weakness has been the focus of much investigation. However, the dominant theory in the field, that lactic acidosis causes muscle fatigue, is unlikely to tell the whole story. Recently, dysregulation of sarcoplasmic reticulum (SR) Ca 2+ release has been associated with impaired muscle function induced by a wide range of stressors, from dystrophy to heart failure to muscle fatigue. Here, we address current understandings of the altered regulation of SR Ca 2+ release during chronic stress, focusing on the role of the SR Ca 2+ release channel known as the type 1 ryanodine receptor.

The present study investigated the influence of a bilateral exhaustive exercise on the stability of bimanual anti-phase coordination pattern and attentional demands. Eight subjects performed the anti-phase coordination pattern in two sessions: an Exhausting Session and a Control Session. During the Exhausting Session, subjects performed the bimanual coordination after exhaustion of forearms muscles (i.e. endurance time test). For the Control Session, no endurance time test was previously designed before the performance of anti-phase coordination. Within these experimental sessions, two levels of load (loaded and unload) and two frequencies (1.75 and 2.25 Hz) were also manipulated during the bimanual task. Attentional demands associated with performing the anti-phase coordination pattern was measured via a probe reaction time task (RT). The results showed that relative phase variability was higher for the fastest frequency after the exhaustive exercise. Moreover, as a result of the previous muscle exercise, the observed phase coupling was less accurate. No significant effect was found concerning the attentional demands as assessed through RT. The present findings suggest that the muscle exhaustion affects bimanual performance at a more peripheral level.

TO THE EDITOR: Fatigue during exercise is a complex phenomenon and has historically been assigned to peripheral mechanisms. Recently more attention is paid to the "central" origin of fatigue, where failure of the motor cortex, changing neurotransmitter concentrations, decreased blood flow, etc., are put forward as underlying mechanisms (3). Both hypotheses (peripheral and central) contain the same "mistake" when isolating the head from the body and vice versa. In their Viewpoint, Robertson and Marino (4) link the prefrontal cortex (PFC) with exercise tolerance and possible fatigue. The PFC could play a role as switchboard during exhaustive exercise, taking part in "decision" making on exercise cessation (4). A declined EEG response to exercise was found in the PFC when exercise intensity increased (5), which confirms previous results with exhaustive exercise in the heat (2). This might indicate that electrocortical activity is diminished at exercise cessation or that other brain areas become more "active" (1). The important message of the recent paper ( ) is that the authors clearly try to explain that the brain integrates several signals and emotions. However, the question remains if the brain really "thinks" and "makes decisions" to avoid catastrophe. It might also be that during exercise the disturbance of peripheral and central homeostasis are integrated and that several neurotransmitter systems influencing frontal and other brain regions overshoot or even become depleted at exhaustion (3). Also, temporary depletion of brain substrates (glucose, glycogen, lactate) could be involved. At this stage we probably don't have the right tools (methods) available to confirm or reject this hypothesis.

The purpose of this study was to examine the changes in peak power output, blood lactate concentrations and surface electromyographic activity (sEMG) of the agonist [vastus lateralis (VL) and vastus medialis (VM)] and the antagonist [biceps femoris (BF)] muscles at two angular positions intervals (90-67°and 23-0°of knee flexion), during a set of 10 repetitions leading to failure of bilateral leg press exercise. Fatiguing exercise resulted in increased blood lactate concentrations, the agonist mean rectified voltage (MRV) at 90-67°of flexion, the antagonist average MRV at 23-0°of flexion and the spectral parameter proposed by Dimitrov (FI nsm5 ) (P \ 0.01-0.05). Significant decreases (P \ 0.01-0.05) were observed in power output, median frequency (F med ) of the agonist muscles at both angular position intervals and of the antagonist muscle at 90-67°of flexion. No changes were observed in the antagonist/agonist MRV activation ratio. The present data suggest that the shift of frequency spectrum to lower frequencies and the accumulation of lactate and/or H ? , but not the antagonist/agonist MRV activation ratio, may be relevant independent factors associated with fatigue.

It is unclear whether accumulation of lactate in skeletal muscle during exercise contributes to muscle fatigue. The purpose of the present study was to examine the effect of lactate infusion on muscle fatigue during prolonged indirect stimulation in situ. For this purpose, the plantaris muscle was electrically stimulated (50 Hz, for 200 ms, every 2.7 s, 5 V) in situ through the sciatic nerve to perform concentric contractions for 60 min while either saline or lactate was infused intravenously (8 rats/group). Lactate infusion (lactate concentration ∼12 mM) attenuated the reduction in submaximal dynamic force (-49 vs. -68% in rats infused with saline; P &lt; 0.05). Maximum dynamic and isometric forces at the end of the period of stimulation were also higher ( P &lt; 0.05) in rats infused with lactate (3.8 ± 0.3 and 4.4 ± 0.3 N) compared with saline (3.1 ± 0.2 and 3.6 ± 0.2 N). The beneficial effect of lactate infusion on muscle force during prolonged stimulation was associated with a ...

Carbohydrate administration increases endurance in man, and this could be associated with a reduction in muscle glycogen utilization in type I but not in type II fibres. Glucose infusion also attenuates fatigue in the rat plantaris muscle (94% type II fibres) stimulated indirectly in situ, but this is not associated with a glycogen sparing effect. The aims of this study were to verify if glucose infusion would attenuate fatigue and would reduce glycogen utilization in a muscle predominantly composed of type I fibres. For this purpose, the soleus muscle (84% type I fibres) was indirectly stimulated in situ in anaesthetized rats for 60 min while infusing either saline or glucose (1 g.kg À1 .h À1 ; plasma glucose 7.7 mmol.l À1 vs. $5 mmol.l À1 with saline only). The experimental data were expressed as the means (SD). With and without glucose, the dynamic force decreased by $20% in the first minute of stimulation. With the infusion of saline, the dynamic force further decreased to 55% of the initial value at the end of the 60min period of stimulation, but when glucose was infused for 60 min, the dynamic force remained constant at 78% of the initial value. When glucose was infused starting at min 30, dynamic force was partially restored. However, muscle glycogen utilization was not significantly different with the infusion of glucose compared to with the infusion of saline. These results suggest that glucose infusion attenuates fatigue in type I muscle fibres, but that this is not associated with any muscle glycogen sparing.

It is commonly agreed that one needs to use a threshold value in the detection of muscle activity timing in electromyographic (EMG) signal analysis. However, the algorithm for threshold determination lacks an agreement between the investigators. In this study we aimed to determine a proper threshold value in an incremental cycling exercise for accurate EMG signal analysis. Nine healthy recreationally active male subjects cycled until exhaustion. EMG recordings were performed on four low extremity muscle groups; gastrocnemius lateralis (GL), gastrocnemius medialis (GM), soleus (SOL) and vastus medialis (VM). We have analyzed our data using three different threshold levels: 25%, 35% and 45% of the mean RMS EMG value. We compared the appropriateness of these threshold values using two criteria: (1) significant correlation between the actual and estimated number of bursts and (2) proximity of the regression line of the actual and estimated number of bursts to the line of identity. It had been possible to find a significant correlation between the actual and estimated number of bursts with the 25, 35 and 45% threshold values for the GL muscle. Correlation analyses for the VM muscle had shown that the number of bursts estimated with the 35% threshold value was found to be significantly correlated with the actual number of bursts. For the GM muscle, it had been possible to predict the burst number by using either the 35% or 45% threshold value and for the SOL muscle the 25% threshold value was found as the best predictor for actual number of burst estimation. Detailed analyses of the actual and estimated number of bursts had shown that success of threshold estimation may differ among muscle groups. Evaluation of our data had clearly shown that it is important to select proper threshold values for correct EMG signal analyses. Using a single threshold value for different exercise intensities and different muscle groups may cause misleading results.

The use of cold applications is common practice in the fields of sports, medicine and physiotherapy. Although controversial, post-exercise cooling is a widely accepted recovery modality and is believed to improve various subjective and/or objective recovery characteristics. One of the most common recovery cooling procedure is cold-water immersion (CWI) where the participant is immersed up to 15 min. Relatively extreme and new forms of external cooling are the use of whole-body cryotherapy (WBC) and partial-body cryotherapy (PBC) where the participant is exposed to very low temperature for few minutes. The aim of cold therapy is to induce the primary sympathetic reaction, in order to facilitate a medical or therapeutically effect. Although research growing in this area, only few studies have directly compared the physiology after a traditional CWI and novel PBC treatment.

Electromyography (EMG) is a technique that registers muscle activity allowing the study of muscle behavior. One such study is the muscle fatigue analysis, which can be defined as the beginning of muscle tiredness and can occur in static or dynamic contractions. There are moments of activity and muscle rest during dynamic contractions, where the latter may not be interesting for some muscle analysis, like muscle fatigue. Therefore, removing muscle inactivity is attractive, but as the signal is not standardized, this process is slower and more individualized. So, this work aims at presenting a muscle fatigue analysis using semi-automatic segmentation of the EMG signal, cutting off the inactivity moments of an electromyography signal obtained during dynamic activity. This analysis consists in calculating the median frequency, a traditional measure to analyze muscle fatigue in static contractions. To assess the efficiency of the proposed method, the median frequency values were compared using manual and semi-automatic segmentation. The result is satisfactory, preserving the desired signal parts for analysis and indicating muscle fatigue as expected.

This study examines the use of electromyography (EMG) in analyzing forearm muscle responses in hand grasping force with swinging motions. We start by establishing the basics of hand grasping force and swinging motions, laying the groundwork for subsequent discussions. The paper critically assesses various EMG techniques, highlighting how they reveal muscle activity during hand grasping in dynamic situations. We explore how swinging motions affect hand grasping force biomechanics, emphasizing the role of EMG in capturing dynamic muscle activity. A thorough examination of methodologies used in EMG studies provides insights into current practices and emerging trends. Practical applications across fields like rehabilitation and robotics underscore the relevance of this research. The study concludes by addressing current challenges and suggesting future research directions. This synthesis provides a straightforward resource for researchers, practitioners, and technologists seeking a deeper understanding of EMG indices in hand-grasping force analysis with swinging action.

This study aimed to establish the effect of cycling mode and cadence on torque, external power output, and lower limb muscle activation during maximal, recumbent, isokinetic cycling. After familiarisation, twelve healthy males completed 6 × 10 s of maximal eccentric (ECC) and concentric (CON) cycling at 20, 40, 60, 80, 100, and 120 rpm with five minutes recovery. Vastus lateralis, medial gastrocnemius, rectus femoris, and biceps femoris surface electromyography was recorded throughout. As cadence increased, peak torque linearly decreased during ECC (350-248 N·m) and CON (239-117 N·m) and peak power increased in a parabolic manner. Crank angle at peak torque increased with cadence in CON (+13°) and decreased in ECC (-9.0°). At all cadences, peak torque (mean +129 N·m, range 111-143 N·m), and power (mean +871 W, range 181-1406 W), were greater during ECC compared to CON. For all recorded muscles the crank angle at peak muscle activation was greater during ECC compared to CON. This dif...

The utilization of muscle triacylglycerols was studied during and after prolonged bicycle ergometer exercise to exhaustion in eight healthy young men. Two days before exercise and in the postexercise recovery period, subjects were fed a carbohydrate-rich diet (65–70% of energy from carbohydrates). Exercise decreased muscle glycogen concentrations from 533 ± 18 to 108 ± 10 mmol/kg dry wt, whereas muscle triacylglycerol concentrations were unaffected (49 ± 5 before vs. 49 ± 8 mmol/kg dry wt after exercise). During the first 18 h after exercise, muscle glycogen concentrations were restored to 409 ± 20 mmol/kg dry wt. In contrast, muscle triacylglycerol concentrations decreased ( P &lt; 0.05) to a nadir of 38 ± 5 mmol/kg dry wt, and muscle lipoprotein lipase activity increased by 72% compared with values before exercise. Pulmonary respiratory exchange ratio values of 0.80–0.82 indicated a relatively high fractional lipid combustion despite the high carbohydrate intake. From 18 to 42 h o...

Background-Analysis of the composition of muscle fibers constituent to a cleft palate could provide significant insight into the cause of velopharyngeal inadequacy. The authors hypothesized that levator veli palatini muscle dysfunction inherent to cleft palates could affect the timing and outcome of cleft palate repair. Methods-Single, permeabilized muscle fibers from levator veli palatini muscles of three normal (n = 19 fibers) and three chemically induced congenital cleft palates (n = 21 fibers) of 14-month-old goats were isolated, and contractile properties were evaluated. The maximum isometric force and rate constants of tension redevelopment (k tr ) were measured, and the specific force and normalized power were calculated for each fiber. Results-The k tr measures indicate that cleft fibers are predominantly fast-fatigable; normal fibers are slow fatigue-resistant: after a 10-minute isometric contraction, fibers from cleft palates had a loss of force 16 percent greater than that from normal palates (p = 0.0001). The cross-sectional areas of the fibers from cleft palates (2750 ± 209 μm 2 ) were greater (p = 0.05) than those from normal palates (2226 ± 143 μm 2 ). Specific forces did not differ between the two groups. Maximum normalized power of fibers from cleft palates (11.05 ± 1.82 W/l) was greater (p = 0.0001) than fibers from normal palates (1.60 ± 0.12 W/l). Conclusions-There are clear physiologic differences in single muscle fibers from cleft palates and normal palates: cleft palate fibers are physiologically fast, have greater fatigability, and have greater power production. Detection of functional and/or fiber type differences in muscles of cleft palates may provide preoperative identification of a patient's susceptibility to velopharyngeal inadequacy and permit early surgical intervention to correct this clinical condition.

The aim of this work is to develop a versatile muscle model and robustly implement it in an existent multibody system dynamics code with natural coordinates. Two different models are included: the first is a Hill-type muscle model that simulates the functioning of the contractile structures both in forward and in inverse dynamic analysis; the second is a dynamic muscular fatigue model that considers the force production history of each muscle and estimates its fitness level using a threecompartment theory approach and a physiological muscle recruitment hierarchy. The existent equations of motion formulation is rearranged to include the referred models using the Newton's method approach. This allows, in a forward dynamics perspective, for the calculation of the system's motion that results from a pattern of given muscle activations, or, in an inverse dynamics perspective, for the computation of the muscle activations that are required to produce a prescribed articular movement. In both perspectives the system presents a redundant nature that is overcome in the latter case using an SQP optimization algorithm. The methodologies and models are applied to several case studies to evaluate their robustness and accuracy. An upper extremity model with seven muscles is designed to evidence the effectiveness of the implementation of a muscle fatigue model in a multibody system. A second model, encompassing the lower extremity musculoskeletal apparatus with twelve muscles, is proposed for the exclusive calculation of muscle activations. The results are presented and conclusions are discussed. The work concludes with a perspective of possible future developments.

Uma das principais causas da fadiga muscular decorrente de esforco e o aumento da concentracao de hidrogenio no meio intracelular, acidificando-o e, consequentemente, influenciando negativamente na performance. A literatura cientifica diz que a suplementacao de bicarbonato de sodio e capaz de atenuar o desequilibrio do pH na pratica esportiva, diminuindo a fadiga e melhorando o desempenho. O presente estudo buscou avaliar os efeitos da suplementacao de bicarbonato de sodio no desempenho de praticantes de musculacao. Os participantes receberam a suplementacao contendo 0,3 g/kg de massa corporal de bicarbonato de sodio e foram submetidos ao treinamento. Analisou-se o lactato sanguineo e a percepcao subjetiva de esforco em dois momentos: sem a suplementacao e com a suplementacao. Os niveis de lactato sanguineo aumentaram em todos os participantes, e a maioria relatou reducao na percepcao subjetiva de esforco. A suplementacao de bicarbonato de sodio se mostrou eficaz em melhorar o desem...

Repetitive upper extremity exercises result in overuse injuries. However, it is challenging to identify the specific causative movements. This study evaluated the effects of different shoulder positions on grip and electrophysiological activity of upper extremity muscles. [Subjects and Methods] Forty subjects ranging from 18 and 30 years of age were analyzed. Surface electromyography and hand grip strength were measured during a range of shoulder exercises and numerous signal processing methods were applied. [Results] The maximum electromyographic activity intensity was observed in the wrist extensors at various angles. Deltoid activity rose significantly during shoulder flexion. [Conclusion] Overhead work causes shoulder muscle fatigue and prevents effective hand function, which affects occupational health and efficiency. Overhead work involves a hazardous position and decreases efficiency. Ergonomic solutions should be developed to prevent muscle fatigue and decreased grip force.

Objective To evaluate the effects of infrared-light-emitting diode (LED) during treadmill training on functional performance. Methods Thirty postmenopausal women aged 50 -60 years were randomly assigned to one of three groups and successfully completed the full study. The three groups were: (1) the LED group, which performed treadmill training associated with phototherapy ( n ϭ 10); (2) the exercise group, which carried out treadmill training only ( n ϭ 10); and (3) the sedentary group, which neither performed physical training nor underwent phototherapy ( n ϭ 10). Training was performed over a period of 6 months, twice a week for 45 min per session at 85 -90% of maximal heart rate, which was obtained during progressive exercise testing. The irradiation parameters were 100 mW, 39 mW/cm 2 and 108 J/cm 2 for 45 min. Quadriceps performance was measured during isokinetic exercise testing at 60 ° /s and 300 ° /s. Results Peak torque did not differ amongst the groups. However, the results showed signifi cantly higher values of power and total work for the LED group ( Δ ϭ 21 ϩ Ϫ 6 W and Δ ϭ 634 ϩ Ϫ 156 J, p Ͻ 0.05) when compared to both the exercise group ( Δ ϭ 13 ϩ Ϫ 10 W and Δ ϭ 410 ϩ Ϫ 270 J) and the sedentary group ( Δ ϭ 10 ϩ Ϫ 9 W and Δ ϭ 357 ϩ Ϫ 327 J). Fatigue was also signifi cantly lower in the LED group ( Δ ϭ Ϫ 7 ϩ Ϫ 4%, p Ͻ 0.05) compared to both the exercise group ( Δ ϭ 3 ϩ Ϫ 8%) and the sedentary group (Δ ϭ Ϫ 2 ϩ Ϫ 6%). Conclusions Infrared-LED during treadmill training may improve quadriceps power and reduce peripheral fatigue in postmenopausal women.

Objective: The objective of this study was to investigate fatigue in the three heads of the triceps brachii (TB) muscle using surface electromyography (sEMG) obtained at 30%, 45% and 60% of maximal voluntary contraction (MVC). Methods: Twenty-five subjects performed isometric elbow extension until failure, and the rate of fatigue (ROF), time to fatigue (TTF) and normalized TTF (NTTF) were statistically analysed. Subsequently, the behaviour of root-mean-square (RMS), mean-power frequency (MPF) and median-power frequency (MDF) under pre-, onset- and post-fatigue conditions were compared. Results: The findings indicated that, among the heads, ROF was statistically significant at 30% and 45% MVC (P&lt;0.05) but TTF and NTTF at all intensities was statistically insignificant (P&gt;0.05). For every head, only TTF was statistically significant (P&lt;0.05) at different intensities. MPF and MDF under pre-, onset- and post-fatigue conditions were statistically significant (P&lt;0.05) among th...

The surface electromyogram (EMG) from active muscle and oxygen uptake (1202) were studied simultaneously to examine changes of motor unit (MU) activity during exercise tests with different ramp increments. Six male subjects performed four exhausting cycle exercises with different ramp slopes of 10, 20, 30 and 40 W. min-1 on different days. The EMG signals taken from the vastus lateralis muscle were stored on a digital data recorder and converted to obtain the integrated EMG (iEMG). The 1202 was measured, with 20-s intervals, by the mixing chamber method. A non-linear increase in iEMG against work load was observed for each exercise in all subjects. The break point of the linear relationship of iEMG was determined by the crossing point of the two regression lines (iEMGbp). Significant differences were obtained in the exercise intensities corresponding to maximal oxygen uptake (1202max) and the iEMGbp between 10 and 30, and 10 and 40W.min -1 ramp exercises (P<0.05). However, no significant differences were obtained in 1202max and 1202 corresponding to the iEMGbp during the four ramp exercises. With respect to the relationship between 1202 and exercise intensity during the ramp increments, the 1202-exercise intensity slope showed significant differences only for the upper half (i.e. above iEMGbp). These results demonstrated that the 1202max and V02 at which a nonlinear increase in iEMG was observed were not varied by the change of ramp slopes but by the exercise intensity corresponding to 1202max and the iEMGbp was varied by the change of ramp slopes. In addition, the significant differences in the 1202 exercise intensity slopes for the upper half of the tests would suggest that the recruitment patterns of MU and/or muscle metabolic state might be considerably altered depending upon the ramp slope increments.

Exercise effectively promotes and preserves cardiorespiratory, neuromuscular, metabolic, and cognitive functions throughout life. The molecular mechanisms underlying the beneficial adaptations to exercise training are, however, still poorly understood. To improve the mechanistic study of specific exercise training adaptations, standardized, physiological, and well-characterized training interventions are required. Therefore, we performed a comprehensive interrogation of systemic changes and muscle-specific cellular and molecular adaptations to voluntary low-resistance wheel running (Run) and progressive high-resistance wheel running (RR) in young male mice. Following 10 weeks of training, both groups showed similar improvements in body composition and peak oxygen uptake (V̇O2peak ), as well as elevated mitochondrial proteins and capillarization markers in the M. plantaris. Run mice clearly outperformed RR mice in a forced treadmill running capacity test, while RR mice displayed increased grip strength as well as superior mass gains in the M. soleus, associated with distinct proteomic changes specifying the two paradigms. Thus, even though both training modalities induce overlapping adaptations, Run interventions preferably improve submaximal running performance, while progressive RR is a valid model to study training-induced gains in grip strength and plantar flexor hypertrophy.

It has been well established that, in addition to the pulmonary involvement, COPD has systemic consequences that can lead to peripheral muscle dysfunction, with greater muscle fatigue, lower exercise tolerance and lower survival in these patients. In view of the negative repercussions of early muscle fatigue in COPD, the objective of this review was to discuss the principal findings in the literature on the metabolic and bioenergy determinants of muscle fatigue, its functional repercussions, as well as the methods for its identification and quantification. The anatomical and functional substrate of higher muscle fatigue in COPD appears to include lower levels of high-energy phosphates, lower mitochondrial density, early lactacidemia, higher serum ammonia and reduced muscle perfusion. These alterations can be revealed by contraction failure, decreased firing rates of motor units and increased recruitment of motor units in a given activity, which can be functionally detected by a reduction in muscle strength, power and endurance. This review article also shows that various types of muscle contraction regimens and protocols have been used in order to detect muscle fatigue in this population. With this understanding, rehabilitation strategies can be developed in order to improve the resistance to muscle fatigue in this population.

Background Because MRI has shown great accuracy in assessing acute muscle injuries, identification of risk factors for reinjury before return to play (RTP) in professional athletes during the healing process could be very relevant. We assessed the value of MRI findings prior to RTP as predictors of reinjury. Methods Retrospective observational study of 59 professional athletes, mean age 26 years, with first-time acute muscle injury and successful rehabilitation ready to RTP. They underwent MRI within 6 days of the injury and within 7 days prior to RTP. The primary outcome was reinjury. Risk of reinjury was assessed using radiological signs in control MRI scans before RTP. The risk was classified as low, medium or high when none, one or two radiological signs were observed, respectively. Results Reinjury occurred in 9 participants, with a rate of 15.2%. None of the baseline MRI-related variables was significantly associated with reinjury. In the control MRI scan performed within 7 da...

The purpose of this study was to research the effects of downhill running and short-time Mellissa Officinalis supplementation on the blood elements in male athletes. For this purpose reason, 20 healthy male swimmers were chosen randomly and were divided into two groups of 10 members. The amount of hemoglobin, hematocrit and leukocytes was measured in the basic level, before and after supplementation. After data collection, the variance analysis test was done for evaluation of time series and also Bonferroni test and the independent t-test were used significantly for evaluation of the differences among groups. Also, the significant level of p&lt;0.05 was used. Evaluation of research findings has shown that after supplementation the blood elements increased less in the group of Mellissa Officinalis L than the other group as a result of downhill running. In general, we conclude that this herbal supplement can decrease the hemoglobin, hematocrit and leukocytes caused by downhill running.

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a rare fatty acids oxidation disorder which is often associated with deficiency of electron transfer flavoprotein dehydrogenase (ETFDH). In this study we reported clinical features and evaluation of expression profile of circulating muscle-specific miRNAs (myomiRs) in two MADD patients carrying different ETFDH gene mutations. Patient 1 was a compound heterozygote for two missense mutations. She showed a late onset MADD clinical phenotype and a significant increase of serum myomiRs. Patient 2, carrying a missense and a frameshift mutation, displayed early onset symptoms and a slight increase of some serum myomiRs.

After a unilateral muscle exercise, the performance of the non-exercised contralateral limb muscle can be also impaired. This crossover fatigue phenomenon is still debated in the literature and very few studies have investigated the influence of eccentric contractions. This study was designed to assess neuromuscular adaptations involved in the crossover fatigue of the non-exercised contralateral knee flexor muscles. Seventeen healthy young men performed a unilateral submaximal eccentric exercise of the right knee flexors until a 20% reduction in maximal voluntary isometric contraction torque was attained in the exercised limb. Before (PRE), immediately after exercise cessation (POST) and 24 hours later (POST24), neuromuscular function and perceived muscle soreness were measured in both the exercised limb and non-exercised limb. In addition, global perceived fatigue was assessed at each measurement time. At POST, significant reductions in maximal voluntary isometric contraction were observed in the exercised limb (-28.1%, p < 0.001) and in the non-exercised limb (-8.5%, p < 0.05), evidencing crossover fatigue. At POST, voluntary activation decreased in the exercised limb only (-6.0%, p < 0.001), while electrically evoked potentiated doublet torque was impaired in both the exercised limb and the non-exercised limb (-11.6%, p = 0.001). In addition, global perceived fatigue significantly increased at POST (p < 0.001). At POST24, all measured variables returned to PRE values, except for perceived muscle soreness scores exhibiting greater values than PRE (p < 0.05). A possible cumulative interaction between peripheral alterations and global perceived fatigue may account for the immediate crossover fatigue observed in the non-exercised limb.

Kearns–Sayre syndrome (KSS) is a rare, multisystem mitochondrial disorder defined by onset before 20 years of age, chronic progressive external ophthalmoplegia (CPEO), and pigmentary retinopathy, often accompanied by cardiac conduction defects, neurological impairment, and endocrine abnormalities. The disease is typically caused by large-scale mitochondrial DNA (mtDNA) deletions, most frequently the “common 4,977 bp deletion,” disrupting oxidative phosphorylation and impairing cellular energy production in high-demand tissues. Epidemiologically, KSS is rare, with a reported prevalence of 1.6 per 100,000 in certain populations, but its true prevalence is likely underestimated due to diagnostic challenges.
Pathophysiologically, skeletal muscle biopsy often reveals ragged red fibers, reflecting mitochondrial proliferation and dysfunction, while ocular pathology demonstrates retinal pigment epithelium degeneration with a characteristic “salt-and-pepper” fundus. Neuropathology may include severe cerebral white matter demyelination, although the exact mechanisms remain unclear. Clinically, patients may present with ptosis, progressive ophthalmoplegia, sensorineural hearing loss, cerebellar ataxia, growth hormone deficiency, diabetes mellitus, or life-threatening cardiac conduction blocks.
Diagnosis requires molecular confirmation of mtDNA deletions, with next-generation sequencing (NGS) of blood or muscle tissue as the gold standard. Ancillary investigations include cerebrospinal fluid analysis, neuroimaging, MR spectroscopy, and comprehensive cardiac evaluation. Management is supportive, focusing on early detection and treatment of complications, including pacemaker implantation, endocrine replacement, folate supplementation, and rehabilitation strategies. Emerging therapeutic approaches, such as heteroplasmy shifting via mitochondrial-targeted nucleases and antioxidant supplementation with Coenzyme Q10 or its synthetic analog EPI-743, hold promise but remain experimental.
Given its progressive course and systemic involvement, KSS requires an interprofessional approach to optimize quality of life, prevent sudden cardiac death, and address treatable metabolic and endocrine dysfunctions.

The physical demands and combative nature of rugby lead to notable levels of muscle damage. In professional rugby, athletes only have a limited timeframe to recover following training sessions and competition. Through the implementation of recovery strategies, sport scientists, practitioners and coaches have sought to reduce the effect of fatigue and allow athletes to recover faster. Although some studies demonstrate that recovery strategies are extensively used by rugby athletes, the research remains equivocal concerning the efficacy of recovery strategies in rugby. Moreover, given the role of inflammation arising from muscle damage in the mediation of protein synthesis mechanisms, some considerations have been raised on the long-term effect of using certain recovery modalities that diminish inflammation. While some studies aimed to understand the effects of recovery modalities during the acute recovery phase (<48 h post-match), others investigated the effect of recovery modalities during a more prolonged timeframe (i.e. during a training week). Regarding the acute effectiveness of different recovery modalities, cold water immersion and contrast baths seem to provide a beneficial effect on creatine kinase clearance, neuromuscular performance and delayed onset of muscle soreness. There is support in the literature concerning the effect of compression garments on enhancing recovery from delayed onset of muscle soreness; however, conflicting findings were observed for the restoration of neuromuscular function with the use of this strategy. Using a short-duration active recovery protocol seems to yield little benefit to recovery from rugby training or competition. Given that cold modalities may potentially affect muscle size adaptations from training, their inclusion should be treated with caution and perhaps restricted to certain periods where athlete readiness is more important than increases in muscle size.

Naclerio, F and Larumbe-Zabala, E. Relative load prediction by velocity and the OMNI-RES 0–10 scale in parallel squat. J Strength Cond Res 31(6): 1585–1591, 2017—This study analyzed the possibility of using movement velocity and the rate of perceived exertion as predictors of relative load in the parallel squat (PSQ) exercise. To determine the full load-velocity and load-rate of perceived exertion relationships, 290 young, resistance-trained athletes (209 males and 81 females) performed a progressive strength test up to the 1 repetition maximum. Longitudinal regression models were used to predict the relative load from the average velocity (AV) and the OMNI-RES 0–10 scale, considering sets as the time-related variable. Two adjusted predictive equations were developed from the association between the relative load and the AV or the rate of perceived exertion expressed after performing several sets of 1–3 repetitions during the progressive test. The resulting 2 models were capable of ...

To determine the relationship between fatigue and post-activation potentiation, we examined the effects of sub-maximal continuous running on neuromuscular function tests, as well as on the squat jump and counter movement jump in endurance athletes. The height of the squat jump and counter movement jump and the estimate of the fast twitch fiber recruiting capabilities were assessed in seven male middle distance runners before and after 40 min of continuous running at an intensity corresponding to the individual lactate threshold. The same test was then repeated after three weeks of specific aerobic training. Since the three variables were strongly correlated, only the estimate of the fast twitch fiber was considered for the results. The subjects showed a significant improvement in the fast twitch fiber recruitment percentage after the 40 min run. Our data show that submaximal physical exercise determined a change in fast twitch muscle fiber recruitment patterns observed when subjects...

Electric utility line workers report high levels of fatigue in forearm muscles when operating a conventional pistol grip control in aerial buckets. This study measured the applied force and surface electromyographic (sEMG) signals from four upper extremity muscles required to operate the pistol grip control in two tasks. The first task was movement of the pistol grip in six directions (up/down, forward/rearward, clockwise/counter-clockwise), and the second task was movement of the bucket from its resting position on the truck bed to an overhead conductor on top of a 40 ft tall pole. The force applied to the pistol grip was measured in 14 aerial bucket trucks, and sEMG activity was measured on eight apprentice line workers. The applied force required to move the pistol grip control in the six directions ranged from 12 to 15 lb. The sEMG activity in the extensor digitorum communis (EDC) forearm muscle was approximately twice as great or more than the other three muscles (flexor digitorum superficialis, triceps, and biceps). Line workers exerted 14 to 30% MVCEMG to move the pistol grip in the six directions. Average %MVCEMG of the EDC to move the bucket from the truck platform to an overhead line ranged from 26 to 30% across the four phases of the task. The sEMG findings from this study provide physiologic evidence to support the anecdotal reports of muscle fatigue from line workers after using the pistol grip control for repeated, long durations.

Overhead line workers have anecdotally reported elevated levels of fatigue in forearm muscles when operating the pistol grip control that maneuvers an aerial bucket on a utility truck. Previous research with surface electromyographic (sEMG) recordings of forearm muscles corroborated these reports of muscle fatigue. A new pistol grip was designed that reduces the applied force by 50% in all directions of movement. In laboratory testing, sEMG signals were recorded from the upper extremity muscles of twenty subjects, who operated a conventional-force pistol grip and the 50% reduced-force control to move a 1/15 scale model of an aerial truck boom. The muscle that resulted in the greatest sEMG activity (extensor digitorum communis (EDC)) was the muscle that workers typically pointed to when they reported forearm muscle fatigue from using the control. The reduced-forced pistol grip decreased EDC sEMG by an average of 5.6%, compared to the conventional control, increasing the maximum endur...

The expression of carbonic anhydrase (CA) XIV was investigated in mouse skeletal muscles. Sarcoplasmic reticulum (SR) and sarcolemmal (SL) membrane fractions were isolated from wild-type (WT) and CA XIV knockout (KO) mice. The CA XIV protein of 54 kDa was present in SR and SL membrane fractions as shown by Western blot analysis. CA activity measurements of WT and KO membrane fractions showed that CA XIV accounts for ∼50% and 66% of the total CA activities determined in the SR and SL fractions, respectively. This indicates the presence of at least one other membrane-associated CA isoform in these membranes, e.g., CA IV, CA IX, or CA XII. Muscle fibers of the extensor digitorum longus (EDL) muscle were immunostained with anti-CA XIV/FITC and anti-sarco(endo)plasmic reticulum Ca2+-ATPase 1/TRITC, with anti-CA XIV/FITC and anti-ryanodine receptor/TRITC, or with anti-CA XIV/FITC and anti-monocarboxylate transporter-4/TRITC. CA XIV was expressed in the plasma membrane and in the longitudi...

This study investigated the variations in muscle fatigue, time to fatigue, and maximum task duration at different levels of production standard time. [Methods] Twenty subjects performed repetitive tasks at three different levels of production standard time corresponding to "normal", "hard" and "very hard". Surface electromyography was used to measure the muscle activity. [Results] The results showed that muscle activity was significantly affected by the production standard time level. Muscle activity increased twice in percentage as the production standard time shifted from hard to very hard (6.9% vs. 12.9%). The muscle activity increased over time, indicating muscle fatigue. The muscle fatigue rate increased for the harder production standard time (Hard: 0.105; Very hard: 0.115), which indicated the associated higher risk of work-related musculoskeletal disorders. Muscle fatigue was also found to occur earlier for hard and very hard production standard times. [Conclusion] It is recommended that the maximum task duration should not exceed 5.6, 2.9, and 2.2 hours for normal, hard, and very hard production standard times, respectively, in order to maintain work performance and minimize the risk of workrelated musculoskeletal disorders.