Análise de parâmetros eletromiográficos durante testes de contrações isométricas fatigantes e do efeito de um treinamento de resistência de curta duração

Abstract

The aim of the present was to analyze the behavior of the electromyographic and amplitude and frequency variables of the longuissimus thoracis muscle during fatiguing test and the effect of a short endurance training. Participated in this study 20 male health subjects, divided into two groups: control group (CG) and training groups (TG). The EMG signals were detected using disposable pre-gelled bipolar surface electrodes (Medi-Trace) with 1cm of diameter and positioned with an inter-electrode distance of 3cm. The electrodes were placed in a bipolar configuration bilaterally over the right longissimus thoracis and left longissimus thoracis muscles leveled at the spinous process L1, displaced 3cm laterally. The EMG system consisted of surface electrodes, electrodes cables and tip plugs, and a biological signal acquisition module with four channels. A gain of 1000, a high pass filter of 20Hz, the low pass filter of 500Hz and the sampling frequency rate of 1000Hz was used. On the day of the experiment the subjects were positioned in the MA ISOSTATION equipment. The trunk was maintained with a flexion of 45º confirmed by goniometer. After, the subjects performed isometric trunk extensions until fatigue. The contraction force value and EMG was recorded. A visual feedback had been provided to subjects to maintain force level as long as possible at 30%, 40%, 50% and 60%. The training was accomplished three times a week during four weeks. The amplitude and frequency parameters of the EMG signal in each test was associated to the exhaustion time within each one of the four load percentages in order to obtain the initial values and the slopes with the linear regression straight lines. The results showed the possibility in identifying the electromyographic fatigue threshold (EMGFT) by means the load combination and by means the 30 seconds protocol. It is also possible to note highs reliable values to the amplitude and frequency variables. Analyzing the frequency banding it is possible to note that the low frequencies are more affected by the fatigue process. Besides, the initial values to the root mean square (RMS) are influenced by the load level, and the median frequency (MF) and the mean power frequency (MPF) are not. About the training protocol, it was verify an increase in the endurance time (ET) to the pos training condition. No difference was found to the EMG variables after training.