External abdominal oblique muscle ultrasonographic thickness changes is not an appropriate surrogate measure of electromyographic activity during isometric trunk contractions
Affiliations: [a] Centre for Health Science Research, Laboratory of Functional Evaluation and Human Motor Performance (LAFUP), Universidade Norte do Paraná, Londrina-PR, Brazil | [b] Doctoral and Master Program in Rehabilitation Sciences UEL/UNOPAR, Londrina-PR, Brazil | [c] Pathokinesiology Laboratory, Centre for Interdisciplinary Research in Rehabilitation of Greater Montreal, Institut de réadaptation Gingras-Lindsay-de-Montréal, Montreal, QC, Canada | [d] School of Rehabilitation, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada | [e] Occupational Health and Safety Research Institute Robert-Sauvé Montreal, QC, Canada
Correspondence:
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Corresponding author: Rubens A. da Silva, Centre for Health Science Research, Laboratory of Functional Evaluation and Human Motor Performance (LAFUP), Universidade Norte do Paraná (UNOPAR), Av. Marseille, 591 – Jd. Piza CEP 86041-120, Londrina-PR, Brazil. Tel.: +11 55 43 3371 7700; E-mail: rubens@kroton.com.br
Abstract: Background:The function of specific abdominal muscles can be assessed using both electromyography (EMG) and ultrasound imaging (USI) thickness measures. However, the relationship between these two measurements is not conclusive during sitting isometric trunk efforts. Objective:This study was conducted to assess the relationship between USI thickness and EMG amplitude measures of the right external oblique (EO) muscle during isometric efforts in the sitting position. Method:Eighteen subjects performed ramp isometric efforts progressing from 0 to 50% of their maximal voluntary contraction (MVC) in three trunk directions on a dynamometer: (1) forward flexion; (2) right lateral flexion; and (3) left axial rotation. USI and surface EMG amplitude measures of the EO muscle were recorded concomitantly and both normalized against rest values and maximal EMG, respectively. Results:EO muscle was significantly more activated (p<0.001) during forward flexion (42% on average) and axial rotation (35%) than during lateral flexion (24%). Non-significant (r=0.01; P=0.979) to highly significant (r=0.98; P<0.0001) and negative and positive Pearson correlations were observed between EMG and EO thickness measures for both flexion and rotation directions. Conclusion:The negative correlations between EMG and USI measures as well as the great variability of these correlations across individuals suggest that USI is not a valid measures of EO muscle activity. USI thickness measures should be interpreted with great caution in research and clinical settings.
