ABSTRACT
This study examined the electromyographic (EMG) responses from the vastus medialis (VM) for electrodes placed over and away from the innervation zone (IZ) during a maximal voluntary isometric contraction (MVIC) and sustained, submaximal isometric muscle action. A linear electrode array was placed on the VM to identify the IZ and muscle fiber pennation angle during an MVIC and sustained isometric muscle action at 50% MVIC. EMG amplitude and frequency parameters were determined from 7 bipolar channels of the electrode array, including over the IZ, as well as 10 mm, 20 mm and 30 mm proximal and distal to the IZ. There were no differences between the channels for the patterns of responses for EMG amplitude or mean power frequency during the sustained, submaximal isometric muscle action; however, there were differences between channels during the MVIC. The results of the present study supported the need to standardize the placement of electrodes on the VM for the assessment of EMG amplitude and mean power frequency. Based on the current findings, it is recommended that electrode placements be distal to the IZ and aligned with the muscle fiber pennation angle during MVICs, as well as sustained, submaximal isometric muscle actions.
Subject(s)
Electromyography/methods , Isometric Contraction , Quadriceps Muscle/physiology , Electrodes , Female , Humans , Male , Quadriceps Muscle/innervation , Young AdultABSTRACT
The purposes of this study were to determine if (a) the log-transformed model can be applied to dynamic exercise and (b) the slope and y-intercept terms can provide additional information above and beyond the polynomial regression analyses. Eleven physically active individuals performed incremental cycle ergometry on a single occasion. Electromyographic electrodes were placed on the three superficial quadriceps muscles to record muscle activation during the exercise test. The patterns of responses for electromyographic amplitude vs power output were analyzed with polynomial and log-transformed regression models. The results of the polynomial regression for the composite data indicated that the best-fit model for the vastus lateralis muscle was linear (R(2) = 0.648, P < 0.0001), whereas the best-fit model for the rectus femoris (R(2) = 0.346, P = 0.013) and vastus medialis (R(2) = 0.764,P = 0.020) muscles was quadratic. One-way repeated measures analyses indicated no significant differences(P > 0.05) across the three superficial quadriceps muscles for the slope and y-intercept terms. These findings suggest that the log-transformed model may be a more versatile statistical approach to examining neuromuscular responses during dynamic exercise.
Subject(s)
Electromyography , Exercise/physiology , Models, Statistical , Quadriceps Muscle/physiology , Adult , Exercise Test , Female , Humans , Linear Models , Male , Regression Analysis , Young AdultABSTRACT
UNLABELLED: The electromyographic (EMG) mean power frequency (MPF) and amplitude versus time relationships are commonly used to characterize localized muscle fatigue. PURPOSE: The purpose of this study was to compare the effect of epoch length on the individual and mean slope coefficients and y-intercepts resulting from the EMG MPF and amplitude versus time relationships of the vastus medialis (VM) muscle during fatiguing isometric muscle actions at 30 and 75% of maximum voluntary isometric contraction (MVC). METHODS: Eight adults performed two continuous, isometric muscle actions of the leg extensors at 30 and 75% MVC to exhaustion. Six, 5.0 s epochs of the surface EMG signals were recorded from the VM during each minute. Epoch lengths of 0.5, 1.0, and 2.0 s were selected from the middle of each 5.0 s epoch. Linear regression was used to estimate the slope coefficient and y-intercept values for the EMG MPF and amplitude versus time relationships for each epoch length (0.5, 1.0, 2.0, and 5.0 s) and subject. RESULTS: There were no significant differences between epoch lengths for the individual or mean slope coefficients or y-intercepts (EMG MPF and amplitude versus time relationships). CONCLUSION: This study indicated that epochs of 0.5 - 5.0 s resulted in the same characterization of EMG (MPF and amplitude) versus time relationships during isometric muscle actions.
Subject(s)
Electromyography/methods , Isometric Contraction/physiology , Leg/physiology , Muscle Fatigue/physiology , Female , Humans , Linear Models , Male , Torque , Young AdultABSTRACT
The purposes of this study were twofold: 1) to derive the mechanomyographic mean power frequency fatigue threshold (MMG MPFFT) for submaximal cycle ergometry; and 2) to compare the power outputs associated to the MMG MPFFT to other neuromuscular and gas exchange fatigue thresholds. 9 adults (5 men and 4 women; mean+/-SD age=23.7+/-3.7 years; body weight=66.3+/-8.2 kg) performed an incremental cycle ergometry test to exhaustion while expired gas samples, electromyographic (EMG), and MMG signals were measured from the vastus lateralis muscle. The non-significant correlations (r=0.17 to 0.66; p>0.05) among the physical working capacity at the fatigue threshold (PWCFT), MMG MPFFT, and gas exchange threshold (GET) suggested that different physiological mechanisms may underlie these 3 fatigue thresholds. A significant correlation (r=0.83) for the MPFFT vs. respiratory compensation point (RCP) suggested that these fatigue thresholds may be mediated by a common physiological mechanism. In addition, the significantly lower mean values found for the PWCFT (mean+/-SD=163+/-43 W), MMG MPFFT (132+/-33 W), and GET (144+/-28 W) than MPFFT (196+/-53 W) and RCP (202+/-41 W) suggested that these gas exchange and neuromuscular fatigue thresholds may demarcate different exercise intensity domains.
Subject(s)
Bicycling/physiology , Exercise Test/methods , Muscle Fatigue/physiology , Adult , Ergometry , Female , Humans , Male , Muscle, Skeletal/physiology , Myography/methods , Pulmonary Gas Exchange/physiology , Young AdultABSTRACT
El carcinoma in situ testicular (CisT) es una lesión considerada precursora de los tumores testiculares de células germinales (TCG). Estudios en pacientes con TCG han mostrado que un 50 porciento de los que tienen un CisT en biopsias del testículo contralateral desarrollan una enfermedad invasora a 5 años, si no sontratados. El objetivo de esta comunicación fue describir la evolución a largo plazo de un grupo de pacientes con diagnóstico de CisT contralateral, en nuestra serie de pacientes con TCG. Este estudio retrospectivo incluye 194 pacientes con orquidectomías radicales por TCG entre enero 1985 y diciembre 1992. Se registraron: datos demográficos de los pacientes, tratamiento, realización de biopsia testicular contralateral, anatomía patológica y seguimiento. La información clínica fue obtenida de una base de datos computarizada y el seguimiento de los pacientes con CisT se realizó a través de registros clínicos, entrevista telefónica y visita médica. La edad promedio de los pacientes fue de 32,2 (4-82) años. Se realizó biopsia testicular contralateral en 30 pacientes (15 porciento). En las biopsias testiculares se observan 5 pacientes (16 porciento) con CisT, 8 (27 porciento) conatrofia y 17 (57 porciento) con tejido normal. Ninguno de los 5 pacientes con CisT tenía antecedentes decriptorquídea. El tiempo de seguimiento medio fue de 159 (138-210) meses para los pacientes con CisT. De éstos, 3 pacientes se controlaron en forma periódica sin recibir tratamiento complementario, un pacientere cibió radioterapia testicular y el otro se realizó una orquidectomía contralateral. De los 4 pacientescon testículo in situ ninguno ha presentado clínica sugerente de tumor testicular. Tampoco han presentado recidiva de enfermedad hasta septiembre de 2003. La prevalencia de CisT (16 porciento) en este grupo de pacientes es superior a la reportada por series extranjeras. No se observó evolución hacia una forma invasora en ninguno de los pacientes con diagnóstico luego de 13 años de seguimiento.
