Análise da fadiga muscular localizada em atletas e sedentários através de parâmetros de freqüência do sinal eletromiográfico

Embora a análise no domínio da freqüência do sinal eletromiográfico (EMG) seja empregada na caracterização do processo de fadiga muscular localizada, sua aplicação, especificamente a da freqüência mediana (Fmed), é pouco explorada no âmbito esportivo. O objetivo do presente estudo foi verificar a viabilidade da aplicação do sinal EMG, através de sua análise no domínio da freqüência, como parâmetro para determinação e diferenciação no comportamento da fadiga muscular localizada. Dois grupos de sujeitos, um caracterizado como atletas (n =12) e outro como sedentários (n =12), foram submetidos a análises baseadas em procedimentos executados em três diferentes situações experimentais, todos envolvendo a modalidade de exercício isométrico: i) teste máximo para determinação da contração isométrica voluntária máxima (CIVM); ii) teste de fadiga, sustentado por 35 seg. a 80% da CIVM; iii) teste de recuperação, sustentado por 10 seg. a 80% da CIVM; neste ultimo foi monitorado o comportamento da Fmed nos três primeiros (Fmedi) e três últimos segundos (Fmedf) do sinal EMG no músculo tibial anterior durante o teste de fadiga. Durante os 10 segundos do teste de recuperação foi calculada a Fmed referente a todo o período (Fmedr). parâmetro utilizado no cálculo do índice de recuperação muscular (IRM). Os resultados apontam que a Fmedf apresentou valor menor em relação à Fmedi em ambos os grupos (p < 0,05). Quando comparado com o grupo de sedentários, o grupo de atletas apresentou valores maiores de Fmedi e Fmedf (p < 0,05). O valor médio e desvio-padrão do IRM para o grupo de atletas foram de 62,1% ± 28,7 e, para o grupo de sedentários, de 55,2% ± 27,8 (p > 0,05). Dessa forma, os resultados apresentados neste estudo permitem inferir a viabilidade na aplicação de parâmetros no domínio da freqüência do sinal EMG para a determinação e diferenciação do comportamento da fadiga muscular localizada.

Análise da reprodutibilidade de parâmetros no domínio da frequência do sinal EMG utilizados na caracterização da fadiga muscular localizada

The aim of this study was to analyze the reproducibility of the electromyography signal's parameters (EMG) in the frequency domain used in the characterization of localized muscle fatigue. Fifteen male subjects underwent a fatigue test based on isometric knee extension, being held at three different times at intervals of seven days. To assess the reproducibility of data between the tests we calculated the correlation coefficient (ICC) for the median frequency (MF) in total exercise time (MFT), MF obtained for every 10% of exercise time (MF10%) and the powers of the frequency bands obtained by dividing the power spectrum at windows of 20 Hz. The results showed: (1) excellent reproducibility for MFT, (2) good reproducibility for MF10%, and (3) greater variation in the signal EMG bands from 20 to 120 Hz, especially at the bands of 20-40 Hz and 40-60 Hz, which showed greater sensitivity to the process of muscle fatigue. We conclude that the MF is a variable that shows good reproducibility and that the fragmented analysis of the power spectrum, by means of frequency bands, showed that significant variations occur in the EMG signal during the installation of the fatigue process, having potential to become a new method for the characterization of localized muscle fatigue.

Influência da fadiga no comportamento neuromuscular do quadríceps femoral, após reconstrução do ligamento cruzado anterior

Muscle fatigue is a phenomenon that promotes physiological and biomechanical disorders and their changes in healthy subjects have been widely studied and have significant importance for care in preventing injuries, but we do not have many information about its effects in patients after ACL reconstruction. Thus, this study is to analyze the effects of fatigue on neuromuscular behavior of quadriceps after ACL reconstruction. To reach this objective, participants were forty men, twenty healthy (26,90 ± 6,29 years) and twenty after ACL reconstruction (29,75 ± 7,01 years) with a graft of semitendinosus and gracilis tendons, between four to six months after surgery. At first, there was an assessment of joint position sense (JPS) at the isokinetic dynamometer at a speed of 5°/s and target angle of 45° to analyze the absolute error of JPS. Next, we applied the a muscle fatigue protocol, running 100 repetitions of isokinetic knee flexion-extension at 90°/s. Concurrently with this protocol, there was the assessment of muscle performance, as the peak torque (PT) and fatigue index, and electromyographic activity (RMS and median frequency). Finally, we repeated the assessment of JPS. The statistical analysis showed that patients after ACL reconstruction have, even under normal conditions, the amended JPS compared with healthy subjects and that after fatigue, both have disturbances in the JPS, but this alteration is significantly exacerbated in patients after ACL reconstruction. About muscle performance, we could notice that these patients have a lower PT, although there are no differences between the dynamometric and EMG fatigue index. These findings show the necessity about the cares of pacients with ACL reconstruction in respect of the risks of articulate instability and overload in ligamentar graft

Efeito do tempo de repouso após fadiga induzida no desempenho neuromuscular do quadríceps femoral: ensaio clínico, controlado, randomizado, cego

Objective: To evaluate the effect of different resting periods, after induced muscle fatigue, in the quadriceps femoris neuromuscular performance, in healthy subjects. Methods: Sixty-four volunteers, of both genders, with an average of 21,8 ± 1,7 years and mean body mass index of 24,2 ± 3,7 Kg/m2 were randomly assigned into 4 groups: control group (was not induced fatigue); Experimental Group 1 (Exp. 1 1 minute of rest after fatigue); Experimental Group 3 (Exp. 3 3 minutes of rest after fatigue) and Experimental Group 5 (Exp. 5 5 minutes of rest after fatigue). The subjects were evaluated to the knee´s joint position sense (JPS), followed by 5 flexion-extension knee concentric isokinetic contractions at 60°/s, with concomitant recording of median frequency (Fmed) of rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM). Then they underwent a muscle fatigue protocol (30 flexion-extension knee concentric contractions at 60°/s) and were reevaluated on the isokinetic performance, Fmed and JPS. Blood lactate levels were measured before initial assessment, immediately after the fatigue protocol and 5 minutes after the end of the rest period. Results: The adoption of 3 minutes of rest was sufficient to restore the initial conditions for the peak torque normalized by body weight and the VL and VM Fmed. The joint position sense returned to its initial values with 1 minute rest. The lactate concentration remained high regardless of the adopted rest period. Conclusion: The use of 3-minute rest period is sufficient for the reestablishment of the neuromuscular parameters to the pre fatigue values.

Efeitos imediatos da laserterapia sobre o desempenho neuromuscular após fadiga muscular induzida: ensaio clínico controlado, randomizado e cego

The aim of this study was to investigate the immediate effects of laser therapy on neuromuscular performance in healthy subjects after a muscle fatigue. This is a clinical trial, controlled, randomized, blinded, attended by 80 volunteers of both genders, healthy, with ages between 18 to 28 years. Initially the volunteers performed an initial evaluation (EV1) using electromyography in the biceps muscle, associated with assessment in isokinetic dynamometry with 5 concentric contractions (60 °/s) for elbow flexion. The subjects were randomly allocated into 4 groups: G1 (control, n = 20), G2 (placebo, n = 20), G3 (pre-fatigue laser, n = 20), and G4 (post fatigue laser, n = 20). The muscular fatigue protocol had 30 concentric isokinetic contractions (120 °/s). We used a 808 nm laser, power of 100 mW, applied at the belly of the biceps muscle. After the speeches the volunteers performed a final evaluation (EV2). Test was applied to two-way ANOVA with post hoc Turkey, with a significance level of 5%. There was no significant difference in electromyographic evaluation. In dynamometric evaluation showed a drop in peak torque, peak torque normalized to body weight (p <0.001) and average power (p <0, 05) between the initial and final evaluations in control. Among the groups there was a significant difference between the control and the other groups in relation to peak torque (p <0.05), peak torque to body weight (p <0.001) and average power (p <0.05). Therefore, the low intensity laser therapy does not alter the immediate neuromuscular performance after fatigue

Validação da escala de fatigabilidade percebida para avaliação da fadiga em idosas

The term fatigability concerns the degree of fatigue associated with performing an activity of any type (physical, mental, emotional and / or social). Recently scales for assessing fatigue in the English language were created, however, gaps exist regarding the validity of these scales in relation to oxygen consumption and levels of perceived fatigue. Objective: To investigate the validity of perceived fatigability scale in older women frail and non-frail by the expired gases kinetics. Methods: This is a study of type validation, where were evaluated 48 elderly. The evaluation was conducted at two different sessions. In the first, data were collected demographic partners, as well as assessment of cognitive function, physical health, and the phenotype of frailty. The second was composed by the test 6-minute walk (6MWT) associated the expired gases kinects and assessment of perceived fatigability. Statistical analysis was performed a descriptive analysis and then we used the Pearson correlation test to evaluate the relationship between the measure of perceived fatigue and variables oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory exchange ratio (RER)before and after 6MWT. We used a linear regression model initially considering the following explanatory variable: age, Body Mass Index (BMI), presence of frailty, comorbidities, level of physical activity, distance covered in the 6MWT , the energy cost of walking and severity of fatigability on performance. Results: The final sample consisted of 44 elderly women, 4 elderly were excluded because they didn t complete all phases of this study. The mean age obtained was 75 years (± 7.2 years). There was no significant correlation between fatigability measures and the values of VO2 ( r = .09 , p = .56 ) , VCO2 ( r = .173 , p = .26 ) , RER ( r = - .121 , p = .43 ). The final linear regression model showed that the energy cost of walking, the usual level of physical activity and the performance severity of fatigability explained 83.5 % (R2 = 0.835, p < 0.01) of the variation in the perceived fatigability. Conclusion: Our findings indicate a relationship between greater severity of fatigability and lower levels of physical activity and increased energy cost in walking, suggesting that the fatigability analyses using a simple numeric scale is valid and viable for assessment of fatigue in older women

Fadiga no trabalho: como o psicólogo pode atuar?

As más condições laborais e a forma de organização do trabalho dentro do sistema capitalista frequentemente têm se mostrado nocivas para o trabalhador. Além disso, a chamada síndrome da fadiga crônica é um dos males que acomete a classe trabalhadora. Por meio de revisão teórica buscou-se caracterizar a síndrome, suas possíveis causas e consequências e o papel do psicólogo nas organizações. A fadiga pode ser compreendida como um esgotamento físico e mental, culminando em consequências para a saúde do trabalhador. Excesso de trabalho, pressão por produção, turnos alternados, riscos físicos e falta de autonomia são alguns fatores apontados como prováveis desencadeadores da síndrome, e as consequências encontradas vão desde baixo rendimento e maior risco de acidentes de trabalho até dificuldade para relaxar em momentos de lazer. É papel do psicólogo do trabalho e organizacional realizar ações remediadoras e preventivas que impeçam ou dificultem o aparecimento da fadiga no trabalho.

Avaliação do efeito de gases poluentes na corrosão metálica: um experimento para o ensino da corrosão

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Análise do efeito higrotérmico no comportamento em fadiga de compósitos de PPS/fibras de carbono

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Avaliação da fissuração por fadiga em tubos durante transporte marítimo

Tubos de aço são transportados diariamente em todo o mundo, por caminhão, trem ou navio. Conseqüentemente, danos de transporte, podem ocorrer com freqüência e regularidade. O tipo de dano particular selecionado para este estudo foi o de trinca por fadiga, o qual é considerado como um dos mais críticos. Neste trabalho foram estudados tubos de aço fabricados de acordo com os requisitos da norma API 5L [1]. Foram efetuadas caracterizações químicas, mecânicas e metalográficas de um tubo com diâmetro 609,6 mm e espessura 15,87 mm grau X-65. A simulação do transporte por navio de tubos de aço foi feita submetendo-se seções de tubo com comprimento igual a 0,1 metro, a ciclos de fadiga por meio de máquina servo-hidráulica. Foi possível concluir que em tubos soldados, a região adjacente ao cordão de solda é a mais crítica, e que quando o posicionamento do tubo na carga é efetuado de maneira que a solda fique apoiada sobre alguma superfície rígida, a ocorrência de trinca por fadiga torna-se possível principalmente se os procedimentos de manuseio, carregamento e transporte não forem executados da maneira como recomendada pelos fabricantes de tubos e pela norma API [2].

A proposta biomecânica para a avaliação de sobrecarga na coluna lombar: efeito de diferentes variáveis demográficas na fadiga muscular

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fadiga de grampos de retenção em prótese parcial removível. Efeito de ligas, espessuras e técnicas de fusão. Parte I.

The authors looked for the verification of the fatigue of retentive clasps utilized on the removable partial denture. According to this, it was idealized and built on assay machine, that through movements, simulate the insertion and removal of the clasp for a pattern tooth, manufactured on cobalt-chromium which has all the preparation normally utilized to the correct confection of this type of prosthesis. It was utilized three different commercial alloys based on cobalt-chromium: L1-Biosil; L2-Steldent; L3-Duracron. It was utilized the T clasp of Roach, with was tested upon three different proportions among width and thickness: E1-1.7;E2-2.0 and E3-2.3 and was casted through two casting techniques: F1-oxygen-gas and F2-oxygen-acetylene. The clasps were tested on the machine, which allowed the reading of the number of insertion and removal cycles made until fatigue appeared. The obtained results were submitted to the statistic analysis and the authors concluded that: a) L3 (Duracrom) obtained the best results followed by L1 (Biosil) and finally L3 (Steldent); b) among the analyzed thickness, the best results were obtained by E3, followed by E2 and after this E1; c) form the casting techniques, F2 gave us the best results.

Fadiga de grampos de retenção em prótese parcial removível. Efeito de ligas, espessuras e técnicas de fusão. Parte II.

The authors tested the T clasp of Roach in three differents proportions among width and thickness: E1-1.7; E2-2.0 and E3-2.3, with a constant length of 15 mm. These clasps were casted with three cobalt-chromium alloys (L1-Biosil; L2-Steldent and L3-Duracrom), through two casting techniques (F1-oxygen-gas and F2-oxygen-acetylene). The fatigue of the clasps were verified by using and assay machine, that through movements, simulate the insertion and removal of the clasps for a pattern which were obtained from a premolar, prepared in a surveyor. This machine detect the fatigue of the clasps and count the number of cycles of insertion and removal realized. The obtained results of the interaction between the analysed factors, were submitted to the statistic analysis and the authors concluded that: a) the interaction of factors, Alloy x Thickness, Alloy x Casting Technique and Thickness x Casting Technique did not change the order of effects that the factors showed separately but gave rise to effects of different magnitude for any observed sense; b) the simultaneous interaction of the factors Alloy x Thickness x Casting Technique confirmed the superiority of the L3 alloy, the thickness E3 and the F2 casting technique.

Fadiga em dormentes de concreto reforçados com fibras de aço

A prestressed concrete monoblock railroad tie was designed to attend the characteristics of a Brazilian railroad track with 1,600 mm gauge and 320 kN axle load. Concrete ties specimens were manufactured without and with steel fibers in a volume fraction of 60 kg/m3 (0.76 % by volume), and three different initial prestress forces. Static and fatigue tests were carried out on the ties. Static tests showed that steel fibers increase the first crack and ultimate bending moments, increase significantly the slip force of the prestressing tendons, reduce crack width, add higher ductility to the ties and decrease the stress in the prestressing tendons. Under dynamic loading the steel fibers decreased the stress in the prestressing tendons by about 50%, which improved significantly the fatigue strength of the tie. A tie without fibers failed after only 150,000 cycles. However, a similar tie, with fibers, resisted 3,000,000 cycles without suffering fatigue failure.

Situación y perspectivas de la minería metálica en Argentina

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