A Finite Element Model Approach to Determine the Influence of Electrode Design and Muscle Architecture on Myoelectric Signal Properties.

INTRODUCTION: Surface electromyography (sEMG) is the measurement of the electrical activity of the skeletal muscle tissue detected at the skin's surface. Typically, a bipolar electrode configuration is used. Most muscles have pennate and/or curved fibres, meaning it is not always feasible to align the bipolar electrodes along the fibres direction. Hence, there is a need to explore how different electrode designs can affect sEMG measurements. METHOD: A three layer finite element (skin, fat, muscle) muscle model was used to explore different electrode designs. The implemented model used as source signal an experimentally recorded intramuscular EMG taken from the biceps brachii muscle of one healthy male. A wavelet based intensity analysis of the simulated sEMG signal was performed to analyze the power of the signal in the time and frequency domain. RESULTS: The model showed muscle tissue causing a bandwidth reduction (to 20-92- Hz). The inter-electrode distance (IED) and the electrode orientation relative to the fibres affected the total power but not the frequency filtering response. The effect of significant misalignment between the electrodes and the fibres (60°- 90°) could be reduced by increasing the IED (25-30 mm), which attenuates signal cancellation. When modelling pennated fibres, the muscle tissue started to act as a low pass filter. The effect of different IED seems to be enhanced in the pennated model, while the filtering response is changed considerably only when the electrodes are close to the signal termination within the model. For pennation angle greater than 20°, more than 50% of the source signal was attenuated, which can be compensated by increasing the IED to 25 mm. CONCLUSION: Differences in tissue filtering properties, shown in our model, indicates that different electrode designs should be considered for muscle with different geometric properties (i.e. pennated muscles)

Estimation of abdominal fat compartments by bioelectrical impedance: the validity of the ViScan measurement system in comparison with MRI

Background/Objectives: Abdominal obesity, more specifically increased intra-abdominal adipose tissue, is strongly associated with increased risk of metabolic disease. Bioelectrical impedance analysis (BIA) has been proposed as a potential method of determining individual abdominal fat compartments in the form of the commercially available ViScan measurement system (Tanita Corporation), but it has yet to be independently validated. The objective of this study was to analyse the validity of the ViScan to assess adult abdominal adiposity across a range of body fatness. Subjects/Methods: This was a cross-sectional study with 74 participants (40 females and 34 males with body mass index (BMI) between 18.5 and 39.6 kg/m2). Total abdominal adipose tissue, subcutaneous abdominal adipose tissue (SAAT) and intra-abdominal adipose tissue (IAAT) were measured by magnetic resonance imaging (MRI). In addition, intra-hepatocellular lipid was obtained by magnetic resonance spectroscopy. Estimates of abdominal adiposity (total and compartmental) were obtained from BIA and anthropometry. Results: ViScan-derived percentage trunk fat strongly and significantly related with total abdominal adipose tissue and SAAT in both lean and overweight/obese individuals, and categorized individuals reliably in terms of total abdominal fat. ViScan-derived ‘visceral’ fat correlated significantly with IAAT but the strength of this relationship was much weaker in overweight/obese individuals, particularly those with higher SAAT, leading to less reliable classification of individuals for IAAT. Conclusions: The ViScan may serve as a useful tool for predicting total abdominal fat, but prediction of visceral fat (IAAT) may be limited, especially in abdominally obese individuals