José Magalhães

Motor imagery in blind subjects: the influence of the previous visual experience.

Mental simulation of movements has been widely used to infer about representational aspects of action. On a daily basis, motor planning and execution depends crucially both upon vision and kinesthesia. What if the former is lost? In this study we investigate the physiological changes induced during a mental simulation task in subjects with early and late onset blindness, analyzing simultaneously stabilometric (body sway), electromyographic (EMG, lateral gastrocnemius) and eletrocardiographic (ECG) signals. Subjects were asked to stand up on a force platform and instructed either to: rest during 20s; count mentally from 1 to 15; imagine themselves executing a bilateral plantar flexion 15 times and execute the same movement 15 times. Discriminant analysis was employed to have access to the differences in the groups with respect to heart rate variability (HRV), EMG and body sway measurements for each condition. We found an overall correct classification of 100 and 90.9%, respectively, for the stabilometric parameters and HRV. This result was found only for the mental simulation task (p<0.05), being absent for resting, counting and executing. Previous studies have shown that motor simulation in a kinesthetic mode strongly associates with somatic and autonomic changes. In late blind subjects, however, movement simulation would tend to unfold with the use of both visual and kinesthetic representations. Thus, our results suggest that early and late blind subjects make use of distinct body representations during motor imagery.

Efeito da estratégia de simulação mental sobre o controle postural

Recent studies have proposed that the mental rotation of body parts can be accomplished by calling upon visual and somatomotor resources which, at a functional level, would correspond to different routes toward a single solution [1]. In this study, we investigated the effect of somato-motor and visual strategies upon the mental simulation of a task that involved postural adjustments. Subjects were asked to stand up on a vertical force platform and instructed either to 1) rest during 20 s (ST), 2) count mentally from 1 to 15 (CO), 3) imagine themselves executing a bilateral plantar flexion 15 times (IM), and 4) execute the same movement 15 times (EX). They were further classified as visual or somato-motor dominant, according to the strategy reported as adopted to perform IM. Mental chronometry showed that mean time spent in IM matched that of EX, differing from CO for both groups. Index of stabilometric modulation during IM was computed by reference to CO. Higher index values for area and amplitude of displacement in the antero posterior (y) axis were found for the somato-motor as compared to the visual group. The stabilometric departure found for visual and somato-motor dominant subjects suggests that each imagery mode activates a distinct subset of cortical and subcortical brain networks.

Comportamento temporal da velocidade de condução de potenciais de ação de unidades motoras sob condições de fadiga muscular

A fadiga muscular, definida como a incapacidade na manutencao de um nivel esperado de forca, tem sido amplamente investigada nas areas clinica e desportiva. Na investigacao dos efeitos da fadiga sobre a regulacao da contracao, a eletromiografia de superficie (SEMG) tem sido uma importante ferramenta eletrodiagnostica, pois diferentes parâmetros de analise podem ser extraidos a partir do sinal de EMG. Dentre estes parâmetros, a velocidade de conducao dos potenciais de acao das unidades motoras (VCPAUMs) tem sido uma variavel importante neste tipo de avaliacao, apesar de comumente ser detectada atraves de tecnicas invasivas, mediante eletrodos de arame ou agulha. Assim, o objetivo deste trabalho foi estimar a VCPAUM atraves da SEMG, avaliando o seu comportamento temporal, em contracoes isometricas realizadas ate a exaustao. Dezoito voluntarios (nove homens e nove mulheres; idade de 25,6 ± 6,8 anos), alunos da EEFD/UFRJ, consentiram em participar do estudo. Os sinais de EMG foram colhidos a partir do musculo biceps braquial direito em tres diferentes niveis (25%, 50 e 75% da carga maxima (CM)), sendo, entao, divididos em tres trechos, correspondentes ao tempo total gasto na tarefa, assim denominados: inicio (T1), meio (T2) e fim (T3). A VCPAUM apresentou reducao temporal durante a passagem pelos trechos (p < 0,0001), comparando todas as cargas. Entretanto, foi observada uma queda abrupta da VCPAUM em T3, principalmente em 50 e 75% da CM (p < 0,05), quando comparadas com a carga de 25% da CM. Os resultados apontam que a VCPAUM sofre modificacoes na medida em que ha uma reducao no pH intracelular, fundamental na permeabilidade da membrana celular e que pode ser decorrente de uma diminuicao no aporte sanguineo, pelo aumento no tempo e no nivel de contracao. Alem disso, a adaptacao no uso da SEMG para a estimativa da VCPAUM mostrou a viabilidade no uso do metodo como ferramenta diagnostica.Muscle fatigue, which is defined as the failure to maintain a required or expected force, has been investigated in both clinical and sports applications. On the investigation of muscle fatigue effects related to muscular control, surface electromyography (SEMG) has been the most common electrodiagnostic method, because some different parameters can be extracted from the EMG signal. Among the parameters, motor units action potential conduction velocity (MUAPCV) has been one of the most important, in spite of being usually detected through indwelling electrodes. Thus, the aim of this work was to estimate MUAPCV through SEMG, detecting its temporal behavior during isometric contractions until exhaustion. Eighteen students from EEFD/UFRJ (9 men and 9 women – mean age 25.6 ± 6.8 years), right handed, consented to participate on this study. The EMG signals were collected from the right biceps braquii muscle through surface electrodes on 3 different levels of isometric contractions (25%, 50 e 75% of maximum load (ML)), which were divided into 3 periods that would define the beginning (P1), the middle (P2), and the end (P3) of the contraction. MUAPCV presented a temporal reduction with fatigue installation, showing a statistical difference among periods (p < 0.0001), comparing all the 3 loads. However, it was observed an abrupt decrease of MUAPCV at P3, mainly for 50 and 75% of ML. The results point out that MUAPCV must be quite sensible to pH reduction and changes on ionic concentrations, defined by blood supply decreases. Furthermore, the adaptations introduced on SEMG to MUAPCV estimation were considered satisfactory, reinforcing this method on electrodiagnostic evaluations.

Interpretation of the mechanisms related to the muscular strength gradation through accelerometry

The aim of this study was to characterize the temporal and spectral components of the muscle contractions in different contraction levels through the accelerometry. Fifteen male and twelve female right-handed individuals participated in this study. The trial was constituted by a maximal workload (MW) test that allowed to determine five different workloads (20%, 40%, 60%, 80% and 100% of MW) which, by its turn, allowed to determine five percentage workloads during the strength test (20%, 40%, 60%, 80%, and 100% of the MW) in isometry during eight seconds each of them. A biaxial accelerometer was put on the muscular abdomen of the right brachii biceps muscle. The mean square root (RMS value), a temporal parameter, and the mean frequency (MFE), a spectral parameter were extracted from the accelerometry signals (MMG signals). Such parameters were analyzed towards the X (perpendicular to the fibers) and Y (parallel to the fibers) directions. Both groups presented a descent behavior pattern of the loaded MFE (Y), and the most accentuated was the female group. The MFE variable (X) in the female group presented similar behavior before the MFE (Y), and it was observed a statistically significant difference only between 20% of the MW and every other workload (p = 0.0022 for 40% and p < 0.0001 for the remaining). The male group did not present any statistically significant difference between workloads. The RMS value (Y) presented an ascent behavior with the workload in both genders, presenting differences between the 20% and 40% workloads of the MW (p = 0.000), and 80% and 100% of the MW (p = 0.01) in the male group. But it was observed no statistically significant difference between workloads in the female group. It is argued that during the muscular contraction, there is non-uniform variations on the fibers diameter, besides the low frequency lateral oscillations. Such information seems to have strong correlation between the type of the fibers, and this could contribute for a better clarification on the possible mechanisms involved in the gradation process of the muscular strength.O objetivo deste estudo foi caracterizar as componentes temporais e espectrais dos abalos musculares em diferentes niveis de contracao muscular atraves da acelerometria. Participaram do estudo 15 individuos do sexo masculino e 12 do feminino, todos destros. O experimento constou de um teste de carga maxima (CM) que permitiu determinar cinco cargas percentuais administradas durante os testes de forca (20%, 40%, 60%, 80% e 100% da CM), em isometria e por oito segundos cada. Um acelerometro biaxial foi colocado sobre o ventre muscular do biceps braquial direito. A raiz media quadratica (valor RMS), um parâmetro temporal, e a frequencia media (FME), um parâmetro espectral, foram extraidas dos sinais de acelerometria (sinal de MMG). Estes parâmetros foram analisados nas direcoes X (perpendicular as fibras) e Y (paralela as fibras). Ambos os grupos apresentaram comportamento decrescente da FME (Y) com a carga, sendo mais pronunciado para o grupo feminino. A variavel FME (X), no grupo feminino, apresentou comportamento semelhante a FME (Y), sendo apenas observada diferenca estatistica significativa entre 20% da CM e todas as demais cargas (p = 0,0022 para 40% e p < 0,0001 para as demais). O grupo masculino nao apresentou diferenca estatistica significativa entre as cargas. O valor RMS (Y) apresentou comportamento crescente com a carga para ambos os grupos, havendo diferencas entre as cargas de 20% e 40% da CM (p = 0,000) e 80%, e 100% da CM (p = 0,01) para o grupo masculino. No entanto, nao foi observada diferenca estatistica significativa entre as cargas para o grupo feminino. Discute-se que durante a contracao muscular ocorrem variacoes nao uniformes do diâmetro da fibra, alem de oscilacoes laterais de baixa frequencia. Estas informacoes parecem ter forte correlacao com a tipagem de fibras, o que poderia contribuir para melhor esclarecer os possiveis mecanismos envolvidos durante o processo de gradacao da forca muscular.

Interpretação dos mecanismos de gradação da força muscular através da acelerometria

The aim of this study was to characterize the temporal and spectral components of the muscle contractions in different contraction levels through the accelerometry. Fifteen male and twelve female right-handed individuals participated in this study. The trial was constituted by a maximal workload (MW) test that allowed to determine five different workloads (20%, 40%, 60%, 80% and 100% of MW) which, by its turn, allowed to determine five percentage workloads during the strength test (20%, 40%, 60%, 80%, and 100% of the MW) in isometry during eight seconds each of them. A biaxial accelerometer was put on the muscular abdomen of the right brachii biceps muscle. The mean square root (RMS value), a temporal parameter, and the mean frequency (MFE), a spectral parameter were extracted from the accelerometry signals (MMG signals). Such parameters were analyzed towards the X (perpendicular to the fibers) and Y (parallel to the fibers) directions. Both groups presented a descent behavior pattern of the loaded MFE (Y), and the most accentuated was the female group. The MFE variable (X) in the female group presented similar behavior before the MFE (Y), and it was observed a statistically significant difference only between 20% of the MW and every other workload (p = 0.0022 for 40% and p < 0.0001 for the remaining). The male group did not present any statistically significant difference between workloads. The RMS value (Y) presented an ascent behavior with the workload in both genders, presenting differences between the 20% and 40% workloads of the MW (p = 0.000), and 80% and 100% of the MW (p = 0.01) in the male group. But it was observed no statistically significant difference between workloads in the female group. It is argued that during the muscular contraction, there is non-uniform variations on the fibers diameter, besides the low frequency lateral oscillations. Such information seems to have strong correlation between the type of the fibers, and this could contribute for a better clarification on the possible mechanisms involved in the gradation process of the muscular strength.O objetivo deste estudo foi caracterizar as componentes temporais e espectrais dos abalos musculares em diferentes niveis de contracao muscular atraves da acelerometria. Participaram do estudo 15 individuos do sexo masculino e 12 do feminino, todos destros. O experimento constou de um teste de carga maxima (CM) que permitiu determinar cinco cargas percentuais administradas durante os testes de forca (20%, 40%, 60%, 80% e 100% da CM), em isometria e por oito segundos cada. Um acelerometro biaxial foi colocado sobre o ventre muscular do biceps braquial direito. A raiz media quadratica (valor RMS), um parâmetro temporal, e a frequencia media (FME), um parâmetro espectral, foram extraidas dos sinais de acelerometria (sinal de MMG). Estes parâmetros foram analisados nas direcoes X (perpendicular as fibras) e Y (paralela as fibras). Ambos os grupos apresentaram comportamento decrescente da FME (Y) com a carga, sendo mais pronunciado para o grupo feminino. A variavel FME (X), no grupo feminino, apresentou comportamento semelhante a FME (Y), sendo apenas observada diferenca estatistica significativa entre 20% da CM e todas as demais cargas (p = 0,0022 para 40% e p < 0,0001 para as demais). O grupo masculino nao apresentou diferenca estatistica significativa entre as cargas. O valor RMS (Y) apresentou comportamento crescente com a carga para ambos os grupos, havendo diferencas entre as cargas de 20% e 40% da CM (p = 0,000) e 80%, e 100% da CM (p = 0,01) para o grupo masculino. No entanto, nao foi observada diferenca estatistica significativa entre as cargas para o grupo feminino. Discute-se que durante a contracao muscular ocorrem variacoes nao uniformes do diâmetro da fibra, alem de oscilacoes laterais de baixa frequencia. Estas informacoes parecem ter forte correlacao com a tipagem de fibras, o que poderia contribuir para melhor esclarecer os possiveis mecanismos envolvidos durante o processo de gradacao da forca muscular.

Temporal behavior of motor units action potential velocity under muscle fatigue conditions

A fadiga muscular, definida como a incapacidade na manutencao de um nivel esperado de forca, tem sido amplamente investigada nas areas clinica e desportiva. Na investigacao dos efeitos da fadiga sobre a regulacao da contracao, a eletromiografia de superficie (SEMG) tem sido uma importante ferramenta eletrodiagnostica, pois diferentes parâmetros de analise podem ser extraidos a partir do sinal de EMG. Dentre estes parâmetros, a velocidade de conducao dos potenciais de acao das unidades motoras (VCPAUMs) tem sido uma variavel importante neste tipo de avaliacao, apesar de comumente ser detectada atraves de tecnicas invasivas, mediante eletrodos de arame ou agulha. Assim, o objetivo deste trabalho foi estimar a VCPAUM atraves da SEMG, avaliando o seu comportamento temporal, em contracoes isometricas realizadas ate a exaustao. Dezoito voluntarios (nove homens e nove mulheres; idade de 25,6 ± 6,8 anos), alunos da EEFD/UFRJ, consentiram em participar do estudo. Os sinais de EMG foram colhidos a partir do musculo biceps braquial direito em tres diferentes niveis (25%, 50 e 75% da carga maxima (CM)), sendo, entao, divididos em tres trechos, correspondentes ao tempo total gasto na tarefa, assim denominados: inicio (T1), meio (T2) e fim (T3). A VCPAUM apresentou reducao temporal durante a passagem pelos trechos (p < 0,0001), comparando todas as cargas. Entretanto, foi observada uma queda abrupta da VCPAUM em T3, principalmente em 50 e 75% da CM (p < 0,05), quando comparadas com a carga de 25% da CM. Os resultados apontam que a VCPAUM sofre modificacoes na medida em que ha uma reducao no pH intracelular, fundamental na permeabilidade da membrana celular e que pode ser decorrente de uma diminuicao no aporte sanguineo, pelo aumento no tempo e no nivel de contracao. Alem disso, a adaptacao no uso da SEMG para a estimativa da VCPAUM mostrou a viabilidade no uso do metodo como ferramenta diagnostica.Muscle fatigue, which is defined as the failure to maintain a required or expected force, has been investigated in both clinical and sports applications. On the investigation of muscle fatigue effects related to muscular control, surface electromyography (SEMG) has been the most common electrodiagnostic method, because some different parameters can be extracted from the EMG signal. Among the parameters, motor units action potential conduction velocity (MUAPCV) has been one of the most important, in spite of being usually detected through indwelling electrodes. Thus, the aim of this work was to estimate MUAPCV through SEMG, detecting its temporal behavior during isometric contractions until exhaustion. Eighteen students from EEFD/UFRJ (9 men and 9 women – mean age 25.6 ± 6.8 years), right handed, consented to participate on this study. The EMG signals were collected from the right biceps braquii muscle through surface electrodes on 3 different levels of isometric contractions (25%, 50 e 75% of maximum load (ML)), which were divided into 3 periods that would define the beginning (P1), the middle (P2), and the end (P3) of the contraction. MUAPCV presented a temporal reduction with fatigue installation, showing a statistical difference among periods (p < 0.0001), comparing all the 3 loads. However, it was observed an abrupt decrease of MUAPCV at P3, mainly for 50 and 75% of ML. The results point out that MUAPCV must be quite sensible to pH reduction and changes on ionic concentrations, defined by blood supply decreases. Furthermore, the adaptations introduced on SEMG to MUAPCV estimation were considered satisfactory, reinforcing this method on electrodiagnostic evaluations.

Law, institutions, and interpretation in Jacques Derrida

In this paper, we would like to advocate for a certain reading of Jacques Derrida’s thinking about law, against the grain of most of his reception in legal studies. In this process, we aim to develop a better theoretical understanding of the dynamics of how law institutes itself, and continues to function as an institution, through interpretive practices that must, on one side, respect the rules of the institution and, at the same time, re-institute it on new grounds, as Jacques Derrida points out in his lecture “Force of Law: The ‘Mystical Foundation of Authority.’” The problem under investigation is how law manages to differentiate itself symbolically from violence and what are the consequences of this concerning legal interpretation. This paper’s partial conclusion is that ultimately we are better off viewing interpretation as neither fully determined by nor fully free from text and/or context.

Interpretacion de los mecanismos de graduación de la fuerza muscular a través de la acelerometria

The aim of this study was to characterize the temporal and spectral components of the muscle contractions in different contraction levels through the accelerometry. Fifteen male and twelve female right-handed individuals participated in this study. The trial was constituted by a maximal workload (MW) test that allowed to determine five different workloads (20%, 40%, 60%, 80% and 100% of MW) which, by its turn, allowed to determine five percentage workloads during the strength test (20%, 40%, 60%, 80%, and 100% of the MW) in isometry during eight seconds each of them. A biaxial accelerometer was put on the muscular abdomen of the right brachii biceps muscle. The mean square root (RMS value), a temporal parameter, and the mean frequency (MFE), a spectral parameter were extracted from the accelerometry signals (MMG signals). Such parameters were analyzed towards the X (perpendicular to the fibers) and Y (parallel to the fibers) directions. Both groups presented a descent behavior pattern of the loaded MFE (Y), and the most accentuated was the female group. The MFE variable (X) in the female group presented similar behavior before the MFE (Y), and it was observed a statistically significant difference only between 20% of the MW and every other workload (p = 0.0022 for 40% and p < 0.0001 for the remaining). The male group did not present any statistically significant difference between workloads. The RMS value (Y) presented an ascent behavior with the workload in both genders, presenting differences between the 20% and 40% workloads of the MW (p = 0.000), and 80% and 100% of the MW (p = 0.01) in the male group. But it was observed no statistically significant difference between workloads in the female group. It is argued that during the muscular contraction, there is non-uniform variations on the fibers diameter, besides the low frequency lateral oscillations. Such information seems to have strong correlation between the type of the fibers, and this could contribute for a better clarification on the possible mechanisms involved in the gradation process of the muscular strength.O objetivo deste estudo foi caracterizar as componentes temporais e espectrais dos abalos musculares em diferentes niveis de contracao muscular atraves da acelerometria. Participaram do estudo 15 individuos do sexo masculino e 12 do feminino, todos destros. O experimento constou de um teste de carga maxima (CM) que permitiu determinar cinco cargas percentuais administradas durante os testes de forca (20%, 40%, 60%, 80% e 100% da CM), em isometria e por oito segundos cada. Um acelerometro biaxial foi colocado sobre o ventre muscular do biceps braquial direito. A raiz media quadratica (valor RMS), um parâmetro temporal, e a frequencia media (FME), um parâmetro espectral, foram extraidas dos sinais de acelerometria (sinal de MMG). Estes parâmetros foram analisados nas direcoes X (perpendicular as fibras) e Y (paralela as fibras). Ambos os grupos apresentaram comportamento decrescente da FME (Y) com a carga, sendo mais pronunciado para o grupo feminino. A variavel FME (X), no grupo feminino, apresentou comportamento semelhante a FME (Y), sendo apenas observada diferenca estatistica significativa entre 20% da CM e todas as demais cargas (p = 0,0022 para 40% e p < 0,0001 para as demais). O grupo masculino nao apresentou diferenca estatistica significativa entre as cargas. O valor RMS (Y) apresentou comportamento crescente com a carga para ambos os grupos, havendo diferencas entre as cargas de 20% e 40% da CM (p = 0,000) e 80%, e 100% da CM (p = 0,01) para o grupo masculino. No entanto, nao foi observada diferenca estatistica significativa entre as cargas para o grupo feminino. Discute-se que durante a contracao muscular ocorrem variacoes nao uniformes do diâmetro da fibra, alem de oscilacoes laterais de baixa frequencia. Estas informacoes parecem ter forte correlacao com a tipagem de fibras, o que poderia contribuir para melhor esclarecer os possiveis mecanismos envolvidos durante o processo de gradacao da forca muscular.

Comportamiento temporal de la velocidad de conducción de potencias de acción de las unidades motoras sobre condiciones de fatiga muscular

A fadiga muscular, definida como a incapacidade na manutencao de um nivel esperado de forca, tem sido amplamente investigada nas areas clinica e desportiva. Na investigacao dos efeitos da fadiga sobre a regulacao da contracao, a eletromiografia de superficie (SEMG) tem sido uma importante ferramenta eletrodiagnostica, pois diferentes parâmetros de analise podem ser extraidos a partir do sinal de EMG. Dentre estes parâmetros, a velocidade de conducao dos potenciais de acao das unidades motoras (VCPAUMs) tem sido uma variavel importante neste tipo de avaliacao, apesar de comumente ser detectada atraves de tecnicas invasivas, mediante eletrodos de arame ou agulha. Assim, o objetivo deste trabalho foi estimar a VCPAUM atraves da SEMG, avaliando o seu comportamento temporal, em contracoes isometricas realizadas ate a exaustao. Dezoito voluntarios (nove homens e nove mulheres; idade de 25,6 ± 6,8 anos), alunos da EEFD/UFRJ, consentiram em participar do estudo. Os sinais de EMG foram colhidos a partir do musculo biceps braquial direito em tres diferentes niveis (25%, 50 e 75% da carga maxima (CM)), sendo, entao, divididos em tres trechos, correspondentes ao tempo total gasto na tarefa, assim denominados: inicio (T1), meio (T2) e fim (T3). A VCPAUM apresentou reducao temporal durante a passagem pelos trechos (p < 0,0001), comparando todas as cargas. Entretanto, foi observada uma queda abrupta da VCPAUM em T3, principalmente em 50 e 75% da CM (p < 0,05), quando comparadas com a carga de 25% da CM. Os resultados apontam que a VCPAUM sofre modificacoes na medida em que ha uma reducao no pH intracelular, fundamental na permeabilidade da membrana celular e que pode ser decorrente de uma diminuicao no aporte sanguineo, pelo aumento no tempo e no nivel de contracao. Alem disso, a adaptacao no uso da SEMG para a estimativa da VCPAUM mostrou a viabilidade no uso do metodo como ferramenta diagnostica.Muscle fatigue, which is defined as the failure to maintain a required or expected force, has been investigated in both clinical and sports applications. On the investigation of muscle fatigue effects related to muscular control, surface electromyography (SEMG) has been the most common electrodiagnostic method, because some different parameters can be extracted from the EMG signal. Among the parameters, motor units action potential conduction velocity (MUAPCV) has been one of the most important, in spite of being usually detected through indwelling electrodes. Thus, the aim of this work was to estimate MUAPCV through SEMG, detecting its temporal behavior during isometric contractions until exhaustion. Eighteen students from EEFD/UFRJ (9 men and 9 women – mean age 25.6 ± 6.8 years), right handed, consented to participate on this study. The EMG signals were collected from the right biceps braquii muscle through surface electrodes on 3 different levels of isometric contractions (25%, 50 e 75% of maximum load (ML)), which were divided into 3 periods that would define the beginning (P1), the middle (P2), and the end (P3) of the contraction. MUAPCV presented a temporal reduction with fatigue installation, showing a statistical difference among periods (p < 0.0001), comparing all the 3 loads. However, it was observed an abrupt decrease of MUAPCV at P3, mainly for 50 and 75% of ML. The results point out that MUAPCV must be quite sensible to pH reduction and changes on ionic concentrations, defined by blood supply decreases. Furthermore, the adaptations introduced on SEMG to MUAPCV estimation were considered satisfactory, reinforcing this method on electrodiagnostic evaluations.