Influence of the subcutaneous fat layer, as measured by ultrasound, skinfold calipers and BMI, on the EMG amplitude

Abstract

Surface electromyography (sEMG) is an important tool to estimate muscular activity at work. There is, however, a great inter-individual variation, even in carefully standardized work tasks. The sEMG signal is attenuated in the subcutaneous tissues, differently for each subject, which requires normalization. This is commonly made in relation to a reference contraction, which by itself, however, introduces a variance. A normalization method that is independent of individual motivation, motor control and pain inhibition would be desirable. The aim of the study was to explore the influence of the subcutaneous tissue thickness on sEMG amplitude. Ultrasound measurements of the muscle to skin surface distance were made bilaterally over the trapezius muscle in 12 females. Skinfold caliper measurements from these sites, as well as from four other sites, were made, body mass index (BMI) was recorded, and sEMG was recorded at maximal and submaximal contractions. The muscle-electrode distance, as measured by ultrasound, explained 33% and 31% (on the dominant and non-dominant sides respectively) of the variance of the sEMG activity at a standardized submaximal contraction (average between the sides, 46%); for maximal contractions the explained variance was 21%. Trapezius skinfold measurements showed poor correlations with sEMG. Instead, the mean of skinfold measurements from other sites explained as much as 68% (submaximal contraction). The corresponding figure for BMI was 67%. In conclusion, skinfold thickness explains a major part of the inter-individual variance in sEMG amplitude, and normalization to this measure is a possibility worth further evaluation.

Normalização EMG: considerações da literatura para avaliação da função muscular

“…Para Mathiassen et al 10 , a contração de referência, por ela mesma, introduz a variabilidade no sinal da EMG. É provável que a variabilidade entre os indivíduos permaneça, independente de uma técnica de normalização em relação ao outro 28 . É pouco provável que algumas das téc-nicas utilizadas atualmente na literatura consiga reverter todas as fontes de erros para se conseguir uma medida precisa de atividade muscular.…”

“…É pouco provável que algumas das téc-nicas utilizadas atualmente na literatura consiga reverter todas as fontes de erros para se conseguir uma medida precisa de atividade muscular. Novos esforços deverão ser colocados em prática com o intuito de se obterem outras formas de normalização da EMG que sejam independente do desempenho individual, mas específica às fontes de variância, tais como o tecido adiposo, distância músculo-eletrodo 28,29 . Nordander et al 28 mostraram uma relação negativa entre a EMG e a quantidade de tecido adiposo subcutânea, com o uso da técnica de contração submáxima.…”

“…Novos esforços deverão ser colocados em prática com o intuito de se obterem outras formas de normalização da EMG que sejam independente do desempenho individual, mas específica às fontes de variância, tais como o tecido adiposo, distância músculo-eletrodo 28,29 . Nordander et al 28 mostraram uma relação negativa entre a EMG e a quantidade de tecido adiposo subcutânea, com o uso da técnica de contração submáxima. Conforme um estudo, 81% da variância dentro do sinal da EMG poderia ser explicada pela variação do tecido adiposo subcutânea 29 .…”

The effects of the force of contraction and elbow joint angle on mean and median frequency analysis for muscle fatigue evaluation

“…Moreover, individual differences in the sEMG signals associated with the anthropometric variables (i.e., the measurement of human individual) have been reported [39][40][41] . The second purpose of this study was therefore to investigate the feasibility to use one or more of the twelve selected anthropometric variables as the criteria to create homogeneous subgroups of the subjects associated with the three relationship cases.…”

“…Individual differences in the sEMG signals have been found, which may be due to human physical variations 39,40 . The second purpose of this study was therefore to investigate the feasibility to use twelve related anthropometric variables of subjects as the criteria to identify homogeneous subgroups related to three relationship cases.…”