Introdução: A dor lombar crônica pode ser definida como dor ou desconforto persistente por mais de 12 semanas nos níveis lombar e sacral da coluna vertebral. Cerca de 5% dos pacientes apresentam comprometimento de raiz nervosa, e uma razão comum é a herniação discal. Os músculos multífido lombar (ML) e transverso do abdome (TrA) são preferencialmente acometidos frente a episódios de dor lombar. Contudo, há escassa literatura que tenha avaliado a fadiga do ML e a capacidade de ativação do TrA em indivíduos com e sem hérnia de disco lombar. Objetivo: Avaliar a fadiga do músculo multífido lombar e a capacidade de ativação do transverso do abdome em indivíduos com hérnia de disco e dor lombar crônica, e controle. Métodos: Participaram do estudo 60 indivíduos com idade entre 20 a 50 anos, divididos em dois grupos: Hérnia Lombar (GHL) com dor há mais de três meses (n=30) e Grupo Controle (GC) sem dor (n=30). A fadiga do multífido lombar foi avaliada com a eletromiografia de superfície durante a realização do teste de esforço de Sorensen e a capacidade de ativação do TrA pela Unidade de Biofeedback Pressórico (UBP). A dor foi avaliada com a escala visual analógica - EVA e questionário McGill de Dor, a incapacidade funcional pelo Índice de incapacidade de Oswestry e o relato de esforço percebido pela escala de Borg. O nível de significância adotado foi de 5%. Na análise dos dados de frequência mediana quanto menor o valor maior a fadiga. Resultados: Houve aumento da fadiga nos dois grupos, porém mais intensa no GHL (p=0,0001) proporcionando a instalação da fadiga em menor tempo (163 s). Na capacidade de ativação do TrA, o GHL apresentou ativação insuficiente (-0,9 mmHg) e GC próximo a valores ideais ( -3,9 mmHg). Na escala de Borg, houve diferença entre os grupos para o esforço inicial (p=0,0002), contudo não foi observado diferença para o esforço final (p=0,0611). O GHL apresentou dor moderada (6,4 cm) quando avaliada pela EVA e pelo Questionário McGill de dor nas categorias sensorial (19,2) afetiva (8,6) e total (36,3) e incapacidade funcional mínima. Conclusão: Os indivíduos com hérnia de disco e dor lombar crônica apresentam maior fadiga do músculo multífido lombar e ativação do transverso do abdome insuficiente quando comparados aos controles. / Introduction: Chronic low back pain can be defined as pain or discomfort lasting more than 12 weeks in the lumbar and sacral levels of the spine. About 5% of patients have nerve root impairment, and the more common etiology is the disc herniation. The lumbar multifidus (LM) and transversus abdominis (TrA) muscles are often affected in low back pain. However, the literature on the fatigue assessment of ML and the ability of TRA activation in individuals with and without lumbar disc herniation is scarce. Objective: To evaluate the lumbar multifidus muscle fatigue and transversus abdominis activation in individuals with disc herniation and chronic low back pain, and control. Methods: The study included 60 subjects aged 20 to 50 years, divided into two groups: lumbar herniated group (GLH) with pain for more than three months (n = 30) and control group (CG) without pain (n = 30). The fatigue of the lumbar multifidus was measured with surface electromyography during the Sorensen test and ability of activation of TRA with Unit Biofeedback pressure (PBU). Pain was assessed by visual analog scale - VAS and McGill pain questionnaire, functional disability by Oswestry Disability Index, and the reporting of perceived exertion with Borg scale. The significance level was established in 5%. Results: We found increased fatigue in both groups however more intense in GLH (p=0.0001) providing the onset of fatigue in less time (163 s). The ability to activate the TrA, the GLH showed insufficient activation (-0.9 mmHg) and CG near the ideal values (-3.9 mmHg). In Borg scale, difference was observed between groups for the initial effort (p = 0.0002), however no difference was observed for the final effort (p = 0.061). The GLH had moderate pain (6.4 cm) when assessed by the VAS and the McGill Pain Questionnaire in sensory (19.2), affective (8.6) and total (36.3) categories and minimal functional disability. Conclusion: Individuals with disc herniation and chronic low back pain have higher fatigue of lumbar multifidus and insufficient transversus abdominis muscle activation when compared to controls.

BACKGROUND AND SIGNIFICANCE. Various studies have identified physical risk factors for musculoskeletal disorders (MSDs) associated with hand harvesting of crops, due to repetitive motions, lifting or carrying of heavy loads, and working in flexed trunk postures. A paucity of research exists on ergonomic risks to tomato farmworkers. The available studies have estimated risk based on self-reports of injury and semi-quantitative measures. METHODS. A partnership between East Tennessee State University (ETSU) and a migrant health center (Rural Medical Services) has identified some of the occupational health needs of this population. With the aid of surface electromyography (sEMG), an objective-quantitative tool, a more refined understanding of ergonomic health risks for this population will be developed. The purpose of this study is to evaluate the muscle load and fatigue induced on the anterior deltoid and upper trapezius muscles during three tasks: driving stakes into the ground, tying of tomatoes to stakes, and hoisting of a 35-pound bucket full of tomatoes. Space for a mock test plot, where the study will be conducted, is available at the ETSU’s Valleybrook facility. Muscle activity recordings will be obtained from 15 tomato farmworkers. Spectral analysis and the amplitude probability distribution function (APDF) will be used to assess fatigue and muscle load respectively. A repeated measures ANOVA will be employed in the study. ANTICIPATED RESULTS. Findings of this study should show that localized muscle loading increases muscle fatigue. Neuromuscular demand should vary, depending on the type of task performed. Stake pounding may show a higher neuromuscular demand than the other tasks. AIM 1. Evaluate the magnitude of muscle activity during three simulated tomato-field tasks and measure the intensity of movement during the stake pounding task. AIM 2. Compare estimates of muscle fatigue and muscle load induced on the anterior deltoid and upper trapezius muscles during three simulated tomato-field tasks.

Falls are the leading cause of injuries among older adults (>65) and frequently result in reduced mobility, loss of independence, decreased quality of life, injury, and death.  Extensive research has been conducted regarding postural coordination and control, and other mechanisms/processes involved in maintaining postural stability.  However, there is relatively limited knowledge regarding the patterns of joint coordination, the underlying postural controller, and efficient methods to assess passive and active musculoskeletal properties relevant to balance.  In the current work, three new methods were developed to address these limitations and also to better understand the effects of localized ankle muscle fatigue, gender, and aging on postural coordination and control. First, two methods were used to evaluate postural coordination.  A wavelet coherence approach was developed and applied to assess the level and pattern of coordination between pairs of joints (i.e., ankle-knee, ankle-trunk, and ankle-head).  In addition, the uncontrolled manifold method was implemented for evaluation of potential whole-body coordination control goals.  Clear patterns of intermittent wavelet coherence were evident, indicating that joint coordination is intermittently executed.  Both in-phase and anti-phase coherence were detected over frequencies of 2.5 -- 4.0 Hz.  Shoulder and head kinematics appeared more likely than the whole-body center of mass as control goals for whole body coordination.  Both aging and ankle muscle fatigue led to a reduction of joint coordination. Second, an intermittent sliding mode controller was developed to model quiet upright stance.  In contrast to most previous postural controllers, which assume continuous control, an intermittent controller was considered more consistent with recent evidence on muscle activity and the results of the first study on postural coordination.  The sliding mode controller was able to accurately track kinematics and kinetics, and generated passive and active ankle torques comparable with previous results.  Ankle fatigue led to an increase in active ankle torque especially among young adults and males. Third, a new method was developed to estimate passive and active mechanical properties at the ankle (e.g., stiffness and damping).  This method was inspired from intermittent control theory, and the earlier results noted.  As opposed to conventional methods, this new method is computationally efficient and does not require external mechanical or sensory perturbations.  The method yielded a ratio of passive to active ankle torques consistent with earlier evidence, and larger passive and active ankle torques among males and older adults.  A post-fatigue increase of active ankle torque was estimated, especially among males and young adults. In addition to providing new analytical methods, the noted studies suggest that older adults have decreased joint coordination and increased ankle stiffness.  As a practical implication of this, fall prevention training programs may benefit from seeking to develop appropriate joint coordination strategies and ankle stiffness magnitudes.  To expand on the current work, future research should consider measuring muscle contraction characteristics at multiple joints and in different postures or activities. / Ph. D.

Muscle fatigue is an intrinsic myoprotective process that prevents damaging ATP depletion during intense or prolonged exercise by limiting ATP demand when ATP production becomes insufficient. One mechanism of fatigue involves a reduction in membrane excitability with the opening of ATP-sensitive K+ (KATP) and ClC-1 Cl- channels, resulting in submaximal sarcoplasmic reticulum Ca2+ release and reduced force generation, but the intracellular signalling pathways for this process is unknown. As a first step toward understanding this process, the objective of this study was to test the hypothesis that adenosine receptors (ARs) and AMPK trigger fatigue when a metabolic stress occurs during muscular activity. Compared to control conditions, a pan-activation of ARs with 10 µM adenosine and NECA initially reduced the fatigue rate during the first 60 s of a 3 min fatigue bout triggered with 1 tetanic contraction every s. An activation of the A1 adenosine receptor (A1R) with 10 and 20 µM ENBA resulted in faster rate of fatigue; an effect blocked by 5 µM DPCPX, an A1R antagonist. At 10 and 20 µM, adenosine, NECA, and ENBA activated AMPK via an increased in T172 phosphorylation. At 10 µM, MK8722, an AMPK agonist, initially caused a reduction in fatigue rate during the first 60 s followed by an increased fatigue rate during the last 2 min of the fatigue bout. Co-activation of ARs and AMPK did not give rise to either an additive or synergistic effect. FDB from AMPK α1-/- and α2-/- mice had faster fatigue rate and greater increased in unstimulated force compared to FDB from AMPK α1+/+ and α2+/+ mice. It is suggested that ARs and AMPK play a role in the mechanism of fatigue when a metabolic stress develops during muscle activity.

Prolonged performance of repetitive movements can lead to muscle fatigue, negatively impacting human performance. As a result, researchers have explored methods to effectively assess and quantify this phenomenon, where surface electromyography (sEMG) is a popular method to reveal information regarding muscle contractions. The continuous wavelet transform (CWT) captures the instantaneous frequency components of signals, which make it suitable for sEMG analyses of dynamic muscle contractions. Moreover, sample entropy (SampEn) can be used to quantify the complexity of the sEMG signal, which provides novel insights for assessing muscle fatigue. However, the amount of research on sEMG complexity analyses to assess muscle fatigue during dynamic contractions is limited. Therefore, the goal of this work was to: 1) calculate and compare the major frequency components (MFC) from CWT and modified SampEn (MSE) of sEMG signals during a repetitive trunk flexion-extension (F-E) task; and 2) determine which sEMG metric is more closely related to ground truth fatigue indicators including the visual analogue scale (VAS), maximum pulling force, and kinematic variability of movements. Seven male and five female participants performed up to twelve sets of 50 repetitive trunk FE movements based on pre-defined stopping criteria. Their VAS and maximum pulling strength were measured immediately after each set. The MFC from CWT and the MSE values were calculated from both the left and the right lumbar erector spinae (LES) throughout the movements. Trunk dynamic kinematic variability of every set was quantified by the spine motion composite index (SMCI). Repeated measures correlation coefficients (r) were used to calculate the relationship between MFC and MSE, as well as between these outcome variables and VAS, maximum pulling force, and SMCI across all participants. Visual inspection revealed that on average that both the MFC and the MSE of sEMG signals decreased as the fatiguing protocol progressed, where a significant correlation was found between the two sEMG metrics (r = 0.270, p = 0.006). No significant correlations were found between the two sEMG measures and the maximum pulling strength (r_MFC = 0.101, p = 0.313; r_MSE = 0.193, p = 0.051). Nevertheless, both sEMG metrics showed significant correlations with fatigue VAS, with the MFC having stronger correlations across all the participants (r_MFC = −0.602, p < 0.001) than the MSE (r_MSE = −0.248, p = 0.011). Significant negative correlations were also observed between the SMCI and both sEMG MFC (r_MFC = −0.268, p = 0.010) and MSE (r_MSE = −0.335, p = 0.001). Both sEMG metrics mapped onto the perceived fatigue and movement pattern variations during the task, suggesting they could be used for assessing fatigue during dynamic movements. However, the MFC had a stronger correlation with participants' perceived fatigue whereas MSE was more strongly correlated with kinematic variability. Continued research is required to further examine these relationships, as well as determine the best method of assessing changes in force output with muscle fatigue.

Low-load blood flow restriction (LLBFR) training has been shown to elicit greater increases in muscle hypertrophy and strength compared to traditional low-load training, yet few studies have compared the effectiveness of different LLBFR protocols. To our knowledge, no previous study has compared the acute neuromuscular changes induced by two common LLBFR protocols: 30-15-15-15 repetitions (BFR-75) and four sets of repetitions performed to volitional failure (BFR-F). Therefore, the purpose of this study was to use surface electromyography (sEMG) to compare changes in muscle excitation and fatigue during BFR-75 and BFR-F protocols. Ten women (mean ± SD age = 22 ± 3.5 years) volunteered to participate in this investigation. Participants performed isokinetic, unilateral, concentric-eccentric, leg extension muscle actions at 30% maximal voluntary isometric contraction torque with BFR applied at 60% arterial occlusion pressure using a 12-centimeter-wide cuff. The sEMG amplitude and frequency values were measured from the rectus femoris muscle during the beginning and end of each set of exercise and analyzed using separate 2 [condition (BFR-75 and BFR-F)] x 8 [time (B1, E1, B2, E2, B3, E3, B4, E4)] repeated measures ANOVAs. For sEMG amplitude, there was no significant 2-way interaction (p = 0.486; ηₚ² = 0.118) or significant main effect for condition (p = 0.617; ηₚ² = 0.038), but there was a significant main effect for time (p < 0.001; ηₚ² = 0.520). SEMG amplitude increased across time during both protocols (B1 < E1, E2, B3, E3, B4, E4, p ≤ 0.001–0.049). For sEMG frequency, there was no significant 2-way interaction (p = 0.847; ηₚ² = 0.064) or significant main effect for condition (p = 0.825; ηₚ² = 0.007), but there was a significant main effect for time (p = 0.006; ηₚ² = 0.478). SEMG frequency decreased across time during both protocols (B1 > E1, B2, E2, B3, E3, B4, E4, p = 0.002–0.035). Thus, the implementation of the BFR-75 and BFR-F protocols elicited comparable neuromuscular responses that were consistent with fatiguing exercise, but investigators and clinicians may consider other factors such as participant/patient comfort, time, and rating of perceived exertion when determining which protocol to use.

No description available.

No description available.

Work-related musculoskeletal disorders (WMSDs) are prevalent in the workplace, and epidemiology studies show that these problems do not tend to diminish. While the use of new and advanced technology has substantially reduced the amount of physical workload, repetitive manual activities are still typically observed in various work settings. Despite their fairly low workload intensity, prolonged repetitive tasks have been associated with the development of musculoskeletal complaints and problems. Research on localized muscle fatigue (LMF) has been viewed as a viable endeavor toward understanding the processes and mechanisms associated with WMSDs. A mounting of evidence on local fatigue during sustained static work has been presented, but much less is known with respect to muscle fatigue during more complex activities. A study was conducted with the primary objectives of determining the repeatability of several commonly used fatigue measures, and to evaluate the presence of long-lasting effects of fatigue from different recovery periods. Based on low-level intermittent arm abductions, findings from this study demonstrated that the use of perceptions of muscular discomfort and muscle strength as fatigue measures was satisfactory. In contrast, electromyography (EMG)-based measures were characterized by a fairly low repeatability. The study also suggested that, whenever practical, two days of recovery should be allotted in studies involving multiple exposures to fatiguing protocols. Long lasting effects of fatigue could be present when shorter amounts of recovery period were assigned. A second study was also carried out to investigate the effects of work parameters (force-level, work-rest ratio, and work cycle) on muscular fatigue during intermittent static efforts. It was suggested that work conditions with muscular contraction level less than 12% MVE was non-fatiguing, irrespective of the values of the work parameters selected. Intermittent work with higher levels of muscle contraction might be acceptable, but it was dependent upon interactions of the other two parameters. The effects of dynamic work conditions on muscle fatigue were investigated in another study. Findings from this third study suggested that muscles responded differently under dynamic conditions and the use of typical EMG measures (dynamic EMG) could be less sensitive. This study further demonstrated that fatigue evaluations during such conditions were difficult, and only a limited number of EMG-based measures could be potentially employed. / Ph. D.

Human postural control is a complex process, but that is critical to understand in order to reduce the prevalence of occupational falls. Localized muscle fatigue (LMF), altered sensory input, and inter-individual differences (e.g. age and gender) have been shown to influence postural control, and numerous methods have been developed in order to quantify such effects. Recently, methods based on statistical mechanics have become popular, and when applied to center of pressure (COP) data, appear to provide new information regarding the postural control system. This study addresses in particular the stabilogram diffusion and Hurst exponent methods. An existing dataset was employed, in which sway during quiet stance was measured under different visual and surface compliance conditions, among both genders and different age groups, as well as before and after induction of localized muscle fatigue at the ankle, knee, torso, and shoulder. The stabilogram diffusion method determines both short-term and long-term diffusion coefficients, which correspond to open- and closed-loop control of posture, respectively. To do so, a "critical point" (or critical time interval) needs to be determined to distinguish between the two diffusion regions. Several limitations are inherent in existing methods to determine this critical point. To address this, a new algorithm was developed, based on a wavelet transform of COP data. The new algorithm is able to detect local maxima over specified frequency bands within COP data; therefore it can identify postural control mechanisms correspondent to those frequency bands. Results showed that older adults had smaller critical time intervals, and indicating that sway control of older adults was essentially different from young adults. Diffusion coefficients show that among young adults, torso LMF significantly compromised sway stability. In contrast, older adults appeared more resistance to LMF. Similar to earlier work, vision was found to play a crucial role in maintaining sway stability, and that stability was worse under eyes-closed (EC) than eyes-opened (EO) conditions. It was also found that the short-term Hurst exponent was not successful at detecting the effects of LMF on sway stability, likely because of a small sample size. The new critical point identification algorithm was verified to have better sensitivity and reliability than the traditional approach. The new algorithm can be used in future work to aid in the assessment of postural control and the mechanisms underlying this control. / Master of Science