Efeitos de dois parâmetros antropométricos no comportamento do sinal mecanomiográfico em testes de força muscular

Abstract

RESUMOApesar da mecanomiografia (MMG) ser uma técnica com crescente destaque em investigações relativas ao fenômeno da contração muscular, poucos trabalhos se dedicaram a entender os possíveis efeitos de variáveis antropométricas no sinal de MMG. Portanto, o objetivo do estudo foi avaliar os efeitos da dobra cutânea e do perímetro do braço no comportamento do sinal de MMG nos domínios do tempo e da freqüência em diferentes níveis de contração isométrica. Participaram do estudo 21 indivíduos do sexo masculino (24,9 ± 7,8 anos) e 21 do feminino (20,7 ± 2,5 anos), todos destros. O protocolo experimental constou de um teste de contração voluntária máxima (CVM) que permitiu determinar cinco cargas percentuais administradas durante os testes de força (20%, 40%, 60%, 80% e 100% da CVM). Um acelerômetro biaxial foi colocado sobre o ventre muscular do bíceps braquial direito. O sinal de MMG foi analisado nos domínios do tempo, mediante o comportamento da amplitude do sinal, por meio do cálculo da raiz média quadrática (valor RMS), e da freqüência, através da freqüência mediana (FM) calculada a partir do seu espectro de potência. Estes parâmetros foram extraídos a partir dos sinais gerados na direção X, perpendicular às fibras musculares. Foram também medidos os parâmetros antropométricos dobra cutânea biciptal (BD_DC_B) e perímetros de braço relaxado (BD_PR) e contraído (BD_PC) no terço médio do braço direito. Ambos os grupos apresentaram um comportamento decrescente da FM com o nível de contração. O valor RMS apresentou comportamento crescente com a carga para ambos os grupos. Houve diferenças estatisticamente significativas (p < 0,05) entre as variáveis antropométricas quando comparados os grupos. Sugere-se que o valor RMS, ao contrário da FM, que poderá sofrer atenuações por parte dos tecidos presentes na interface entre o músculo e o transdutor, seja mais consistente na discriminação da força muscular.Palavras-chave: mecanomiografia, MMG, sinal de MMG, vibromiografia, VMG. ABSTRACTIn spite of being a useful method on muscle contraction analysis, few studies have been dedicated to understand how some anthropometrical parameters can interfere in the mechanomyographic (MMG) signal properties. Therefore, the aim of this study was to evaluate the effects of skinfold thickness and arm circumference in the MMG signal behavior in the temporal and frequency domains at different levels of isometric contraction. Twenty-one males (24.9 ± 7.8 years) and 21 females (20.7 ± 2.5 years), all right-handed, participated in this study. Prior to the MMG signals collection, a maximum voluntary contraction test (MVC) was performed to further determine the five levels (20%, 40%, 60%, 80% and 100% of CVM) used during the tests. The two groups performed isometric contractions in the five different levels while MMG signal was collected from the right biceps brachii muscle by a biaxial accelerometer. The root mean square value (RMS), and the median frequency (MF) calculated from the MMG power spectrum were extracted from the MMG signals in X di...

Influence of subcutaneous fat on mechanomyographic signals at three levels of voluntary effort

“…Such results corroborate the study by Polato et al (2008), which used a biaxial sensor to evaluate the relation between the behavior of the MMG signal and median frequency (MDF) of the brachial biceps muscle in different levels of isometric contraction (20%, 40%, 60%, 80%, and 100% MVC) of male and female individuals. Polato et al (2008) associated the decrease in MMG signal of the women to the fact that the subcutaneous fat layer of these groups is thicker, which is similar to the results of da Matta et al (2005). According to Krueger et al (2013), when MDF and ST were analyzed, indication that the fat tissue worked as a low-pass filter for the rectus femoris muscle MMG signals was found for axes X and Y.…”

“…Studies with different force levels (Cochrane et al, 2015;Cooper et al, 2014;Jaskólska et al, 2003;Polato et al, 2008) reported significant differences when evaluating different intensities of isometric force with ST in larger and smaller fat layers. However, those researchers did not show if there is a trend related to different force levels or if this influence occurs in all (three) accelerometers axes.…”

Cortical Reorganization after Hand Immobilization: The beta qEEG Spectral Coherence Evidences

“…In order to obtain signals from the accelerometer we used the model MMA7340 of Freescale semiconductors. This system is formed by microelectronics mechanisms (MEMS), which explore the mechanical proprieties of silicone to create movable structures and to detect distinct movement directions [18] , [19] , [20] . The capture of movements was conducted in actual time system with the interaction of EEG software signal acquisition.…”

Impact of Skinfold Thickness on Wavelet-Based Mechanomyographic Signal

“…It allows that an increase in the fat layer does not generate significantly change in the total energy of signal. Polato et al [35], using biaxial MMG found that the ST raises and MMG values decrease significantly (r = -0.3935, p = 0.0099), therefore without the specification of frequencies that are influenced by ST. Figures 2, 3 and 4 show the RMS average to each frequency band across the participants. Axes Y and X presented greater averages to 11 Hz in group II.…”