Serratus anterior sEMG - sensor placement and test position for normalization purposes during maximal and submaximal...

There is great variability regarding serratus anterior sEMG sensor placement and test positions during normalization procedures. We investigated between-trials reliability of serratus anterior sEMG, acquired at two sensor placements and four test positions, during maximal and submaximal isometric contractions. Twenty young healthy women participated. sEMG was captured at the 7^th intercostal space and at the xiphoid process level, in the mid-axillary line, during maximal and submaximal isometric contractions, in four test positions. Intraclass Correlation Coefficient (ICC_2,1), coefficient of variation and standard error of measurement were calculated. Interactions between sensor placements and test positions were investigated using a two-way repeated-measures ANOVA. All test conditions presented ICC_2,1 > 0.8. There was no interaction between sensor placement and test position. Signal obtained from the sensor at 7^th intercostal space was more stable between-trials and showed higher amplitude, during maximal and submaximal contractions, at seated positions with shoulder protracted at both 90° or 125° of flexion. We suggest to acquire serratus anterior sEMG at the 7th intercostal space and perform maximal or submaximal isometric contractions for signal normalization with shoulder protracted and flexed, at seated position.