Evaluation of the electromyographic signal and the histomorphometry of vastus lateralis muscle in different electrodes placement, intensities of contraction and genders / Avaliação do sinal eletromiografico e da histomorfometria do musculo vasto lateral em diferentes posicionamentos de eletrodos, intensidades de contração e generos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

It has been shown that electromyography signal (EMGs) and histomorphometry are different along the muscle belly and between genders, although the relationship between these parameters is not clear. The aim of this study was to evaluate the EMGs in different intensities of volunteer isometric muscle contraction (10-100%) and electrodes positions over the belly of vastus lateralis muscle [proximal (VLP) and distal (VLD) portions], as well as the histomorphometry for both genders. Eleven women (22,0 ± 2,1 years) and seven men (23,3 ± 2,5 years), took part in the study. All subjects had no lesions in lower limbs. At first a baseline was made to determine the maximum force of leg extension [MM-100 load cell (KRATOS®)]. For EMG recording an EMG-1000 acquisition module (Lynx®) was used (16 bits of resolution, band-pass filter of 201000Hz and sampling frequency of 2000Hz). Two simple differential surface active electrodes (Lynx®, 20 times gain) separated by 10mm were placed over VLP and VLD muscles bellies. Reference electrode was attached to the anterior tibial tuberosity of the evaluated leg. EMGs was recorded simultaneously in both electrodes in different intensities of contraction for 5 seconds, repeated for 3 times and with one-minute intervals among contractions. Load cell signals were also recorded. EMGs were analyzed in Matlab® 6.5.1 software and RMS and median frequency (MF) values were obtained. After EMGs recordings, the muscle biopsies of VLP and VLD were performed using a Bergström needle. Histological sections (12um) were performed in cryostat (MICRON HM 505E at -25°C). The main types of muscle fibers (I, IIA and IID) were identified by mATPase technique and fibers area (um2) was analyzed in Image Manager software (Leica Microsystems®). ANOVA test and Tukey post-hoc test, paired and non-paired Student t test, paired Student t test and Pearson test (correlations). A significant elevation of RMS was observed with the rise of contraction intensity (10-100% maximum voluntary isometric contraction - MVIC) for both genders and electrodes positions. In general, there were no variations in MF with the rise of contraction intensity (for both genders and electrodes positions). Force and absolute RMS values were higher in men compared to women for both electrodes. MF was not different between genders. For fiber types distribution (%) there was no difference between genders and between electrodes positions. However, male s fibers areas were greater than women s and, as a general matter, there was no difference between the electrodes. A positive correlation was observed between force x type I and II fiber areas, RMS x type I and II fiber areas. There was no significant correlation between fibers area and MF and between force and MF. According to our results the fiber type s distribution was not different between genders and electrodes; nevertheless, higher RMS and force values, as well as greater fibers areas, were found in male group. MF was not different between genders. Finally, muscle fibers area did influence RMS and force of vastus lateralis muscle and we suggest that this could be the reason of the observed differences between genders.

ASSUNTO(S)

muscle fibers slow-twitch eletromiografia electromyography muscle fibers fast-twitch electrodes musculo fibras musculares de contração lenta eletrodos muscle

ACESSO AO ARTIGO

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