Study of myoelectric activity in isometric exercises with different contractions

Emanuele Moraes Mello
Biomedical Engineering Laboratory and Neuroscience Program, University of Sao Paulo

Neri Alves
Departamento de F?sica, Qu?mica e Biologia, Universidade Estadual Paulista

Luciana Sanae Ota
Departamento de Fisioterapia, Universidade Estadual Paulista

Fabio Micolis Azevedo
Departamento de Fisioterapia, Universidade Estadual Paulista

Ruben Faria Negr?o Filho
Departamento de Fisioterapia, Universidade Estadual Paulista

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     Last modified: March 13, 2007

Abstract
The aim of the present study is an evaluation of isometric exercises in different ways and levels of force, by the surface electromyography (EMG) parameters. Two forms of isometric exercises were studied: dissipative and conservative. The first one was obtained by the traction of a steel cable fastened to the system, being maintained from such a way to provide 90? of flexing of the elbow; in the other one, the resistance was applied through weights, whose value is equal to the load developed previously. In both situations the forearm was maintained in supine position and the load was controlled by feedback visual. Twenty young male volunteers participated in this study which was approved by the Local Ethic Committee. Half of those carried out isometric actions with 100% maximal voluntary contraction (MVC); and the others carried out with 10% and 50% MVC. All the isometric exercises were done in 10 repetitions of the 3 seconds each - both dissipative and conservative types, in random order for execution. Surface EMG was detected from biceps brachial, long and lateral triceps brachial. For signal processing was used the software Matlab (version 6.1), that applies Butterworth digital filter of fourth order (bandwidth = 10 - 500 Hz). The root mean square (RMS) was analyzed in time domain as well the power spectral density (PSD) and the spectral distribution function (SDF) in the frequency domain. The analysis of the differences between the exercises, for which level of force, was carried out by use of the Student?s t-test. Visualization techniques were also used in analyzes. The parameters of EMG signal showed differences between dissipative and conservative exercises depending on the level of force applied. The differences enlarged while higher levels of force were used for the three muscles, mainly in 100% MVC. The results showed in this work permit to infer that the dissipative have larger muscular activation and bigger activation of slow twitch fibers; whereas in the conservative there are smaller muscular activation and larger activation of fast twitch fibers. Additionally, these results can be important to who use isometric protocols. We believed that in the clinical rehabilitation, when the objective is increasing the muscular force, the activity developed with dissipative exercise can present better results than the conservative. Otherwise, when the objective is improving the motor control or muscular coordination, the activity developed with conservative exercise can present more interesting results compared with dissipative.