Motor unit activity and surface electromyogram power spectrum during increasing force of contraction

Abstract

Twelve male subjects were tested to determine the relationship between motor unit (MU) activities and surface electromyogram (EMG) power spectral parameters with contractions increasing linearly from zero to 80% of maximal voluntary contraction (MVC). Intramuscular spike and surface EMG signals recorded simultaneously from biceps brachii were analyzed by means of a computer-aided intramuscular MU spike amplitude-frequency (ISAF) histogram and an EMG frequency power spectral analysis. All measurements were made in triplicate and averaged. Results indicate that there were highly significant increases in surface EMG amplitude (71 +/- 31.3 to 505 +/- 188 microV, p less than 0.01) and mean power frequency (89 +/- 13.3 to 123 +/- 23.5 Hz, p less than 0.01) with increasing force. These changes were accompanied by progressive increases in the firing frequency of MU's initially recruited, and of newly recruited MU's with relatively larger spike amplitudes. The group data in the ISAF histograms revealed significant increases in mean spike amplitude (412 +/- 79 to 972 +/- 117 microV, p less than 0.01) and mean firing frequency (17.8 +/- 5.4 to 24.7 +/- 4.1 Hz, p less than 0.01). These data suggest that surface EMG spectral analysis can provide a sensitive measure of the relative changes in MU activity during increasing force output.

The effects of the force of contraction and elbow joint angle on mean and median frequency analysis for muscle fatigue evaluation

“…Zipp 56 reported that the high-pass electrode filter characteristic compensates for the low-pass tissue filter characteristic, and then allowing improved observation of force induced spectral changes. A small interelectrode distance of less than 10 mm can produce the results which were dependent of force level 34 , while larger inter-electrode distances of equal or more than 20 mm can give the results which were independent of force 26,34,36 . However, in the present study an inter-electrode distance of 20 mm was used with a fix location of the surface electrodes over the muscle and the three relationship cases were found.…”

Correlation between Facial Patterns and Function of the Masticatory Muscles in Girls and Women.

“…This was thought to be due to the differences in the synchronization phenomena of the NMU by Buchthal and Handsen 1) , and to the ratio of innervation by the muscles and components of kinetic NMU-tonic NMU by Moritani and Muro 10) . With regard to the functional differences between the temporal and masseter muscles, it has been reported that recovery from muscular fatigue was faster in the temporal muscle and that the masseter muscle was more influenced by muscular fatigue 19) .…”

Normalização EMG: considerações da literatura para avaliação da função muscular

“…É possível analisar o sinal da EMG, tanto no domínio temporal como em frequência. No que se refere aos parâmetros da EMG no domínio do tempo, uma medida preconizada na literatura é a amplitude do sinal da EMG, chamada de Root Mean Square (RMS) 2 . Outros parâmetros, tais como amplitude da EMG integrada e envelope linear, também são utilizados para avaliar a ativação muscular 2 .…”

“…No que se refere aos parâmetros da EMG no domínio do tempo, uma medida preconizada na literatura é a amplitude do sinal da EMG, chamada de Root Mean Square (RMS) 2 . Outros parâmetros, tais como amplitude da EMG integrada e envelope linear, também são utilizados para avaliar a ativação muscular 2 . Em geral, a medida que a força aumenta, durante uma contração voluntá-ria isométrica máxima, a amplitude do sinal da EMG também aumenta, caracterizando então a relação EMG-força 1,2 .…”

“…Outros parâmetros, tais como amplitude da EMG integrada e envelope linear, também são utilizados para avaliar a ativação muscular 2 . Em geral, a medida que a força aumenta, durante uma contração voluntá-ria isométrica máxima, a amplitude do sinal da EMG também aumenta, caracterizando então a relação EMG-força 1,2 . A força muscular varia em relação a quantidade de UMs ativas.…”