RESUMO
There is currently little information on the positioning of reference electrode (RE). It is generally accepted that it must be positioned on electrically neutral tissues, such as tendons or bony prominences. The objective of this study is to analyze the characteristics of the electromyographic signal (EMG) for different positions of RE as well as at different levels of muscle contraction. Signals from the brachial biceps and triceps were recorded from 18 healthy women (BMI: 21.20 kg/m2 ± 1.72; mean age: 21.94 ± 1.98 years old) during 100 and 50% maximum flexion voluntary isometric contractions, as well as at rest. For each situation, the RE was randomly positioned in 4 different locations: a) homolateral acromion; b) homolateral brachial biceps; c) styloid process of the contralateral ulna; and d) lateral malleolus of the contralateral ankle. For statistical analysis, Shapiro-Wilk and Kruskal-Wallis tests were used, followed by Dunn's post-hoc test, at a significance level of 5% (p < 0.05). RMS, normalized RMS, PSD, median frequency and levels of energy at 60 Hz, 120 Hz and 180 Hz were assessed for the different sites of RE. The results show that the positioning of the RE on the four experimental locations did not change important features of the electromyographic signals in the time and frequency domains, for the three levels of isometric contractions studied. Such findings compel us to re-think the current trend regarding the RE position followed by the great majority of the researches in areas such as physical therapy.
Assuntos
Eletrodos , Eletromiografia , Contração Muscular , Adulto , Eletromiografia/instrumentação , Eletromiografia/métodos , Feminino , Humanos , Contração Isométrica , Músculo Esquelético , Adulto JovemRESUMO
The objective of this study was to assess electromyographic features of the brachial biceps muscle after the application of cryotherapy and short-wave diathermy. Sixty healthy volunteers participated in the study and were equally divided into three groups: cryotherapy - application of ice packs for 30 min; short-wave diathermy for 20 min; and control. The thermal agents were applied to the anterior and posterior regions of the non-dominant arm. The electromyographic (EMG) signal from the brachial biceps was recorded before and after the application of thermal agents during flexion of the elbow joint at 25%, 50%, 75% of a maximum voluntary isometric contraction defined at least two days before the actual experiments (MVICbl). The volunteers also were asked to execute a free MVIC before and after the application of the thermal agents (MVIC free). A linear regression model with mixed effects (random and fixed) was used. Intra-group analysis showed a reduction in root mean square (RMS) at MVIC free, with no change in the median frequency of the EMG signal at any contraction level for the short-wave diathermy group. An increase on RMS values and a decrease on median frequencies were found after the application of cryotherapy for all contraction levels. The results imply that cryotherapy plays an important role on changing neuromuscular responses at various levels of muscle contraction. Therapists should be aware of that and carefully consider its use prior to activities in which neuromuscular precision is required.