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. 2022 May;10(9):e15295.
doi: 10.14814/phy2.15295.

Verification of surface electromyographic activity of the oblique externus abdominis using ultrasound shear wave elastography

Kentaro Chino  1   2 , Ryosuke Ando  3 , Yasuhiro Suzuki  3   4
Affiliations

Verification of surface electromyographic activity of the oblique externus abdominis using ultrasound shear wave elastography

Kentaro Chino et al. Physiol Rep. 2022 May.

Abstract

This study used ultrasound shear wave elastography (SWE) to revalidate whether surface electromyographic (EMG) electrodes placed on the oblique externus abdominis (OE) can detect only the OE activity without the confounding activity of the underlying oblique internus abdominis (OI). During left and right trunk rotations, the EMG activity was acquired using surface EMG electrodes placed on the right OE. Shear wave velocity (Vs ) values of the right OE and OI were acquired using SWE. The EMG activity during the left and right trunk rotations significantly increased as the level of exertion increased (25%, 50%, 75%, and 100% of the one-repetition maximum [1RM]). The Vs of the right OE was significantly different only between 25% and 75% 1RM in the right trunk rotation, but significantly increased from 25% to 75% 1RM during the left trunk rotation. The Vs of the right OI during the right trunk rotation significantly increased with increased levels of exertion, except between 50% and 75% 1RM. The results for the Vs of the OE and OI in the right trunk rotation suggest that surface EMG electrodes placed on the OE would detect not only the antagonistic OE activity but also the agonistic OI activity.

Keywords: abdominal muscles; oblique internus abdominis; signal crosstalk; surface electromyography; trunk rotation.

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Conflict of interest statement

The authors declare that they have no conflicts of interest associated with this manuscript.

Figures

FIGURE 1
FIGURE 1
Schematic representation of the average fiber direction of the oblique externus abdominis (OE) and oblique internus abdominis (OI) muscles, and the direction of trunk rotation. The average fiber directions of the OE and OI are drawn based on those reported by Brown et al. (2011). The fiber direction of the OE is nearly perpendicular to that of the underlying OI. Therefore, unilateral contractions of the OE and OI lead to trunk rotation in the opposite directions: The right OE produces trunk rotation to the left, while the right OI produces trunk rotation to the right
FIGURE 2
FIGURE 2
Experimental setup for muscle activity measurements by (a) surface electromyography (EMG) and (b and c) ultrasound shear wave elastography (SWE). The illustration shows the placement of the surface EMG sensor and the ultrasound probe at the same site on the skin surface. Participants faced forward with their lower bodies rotated on a swivel to the right or left while maintaining the position for 5 s against the weight. A 1.5 × 1.5 cm region of interest for ultrasound SWE indicated by the white square was placed on the oblique externus abdominis (OE) or oblique internus abdominis (OI), and the average shear wave velocity of the OE and OI indicated by the yellow dotted line was quantified
FIGURE 3
FIGURE 3
Typical surface electromyographic (EMG) signals during right (top) and left (bottom) trunk rotations are acquired using surface EMG electrodes placed on the right oblique externus abdominis. The loads during the trunk rotation were set at 25%, 50%, 75%, and 100% of the one‐repetition maximum (1RM)
FIGURE 4
FIGURE 4
Relationship between the level of exertion and the surface electromyographic (EMG) amplitude in left and right trunk rotations. The levels of exertion shown are equivalent to 25%, 50%, 75%, and 100% of the one‐repetition maximum (1RM). The root mean square amplitudes of the EMG signals during each trunk rotation are normalized to the amplitude during the left trunk rotation at 100% 1RM. The EMG amplitudes of both the left and right trunk rotations were significantly different for all combinations of the exertion levels
FIGURE 5
FIGURE 5
Typical color‐coded elasticity maps of the right oblique externus abdominis (OE) and right oblique internus abdominis (OI) during left and right trunk rotations. The elasticity maps were acquired using ultrasound shear wave elastography (SWE) at rest and during left and right trunk rotations at 25%, 50%, 75%, and 100% of the one‐repetition maximum (1RM). The 1.5 × 1.5 cm white squares indicate the region of interest for ultrasound SWE, and the yellow dotted line indicates the area where the average shear wave velocity of the OE and OI was quantified
FIGURE 6
FIGURE 6
Relationship between the level of exertion and shear wave velocity in left and right trunk rotations. The levels of exertion shown are 0%, 25%, 50%, 75%, and 100% of the one‐repetition maximum (1RM). *Statistically significant for 0% 1RM (i.e., at rest). §Statistically significant for 25% 1RM. †Statistically significant for 50% 1RM. #Statistically significant for 75% 1RM
FIGURE 7
FIGURE 7
Relationship between the EMG amplitude and shear wave velocity (Vs) of the oblique externus abdominis (OE) and oblique internus abdominis (OI). The data obtained from all participants (n = 10) are plotted together. The EMG amplitude at each level of exertion at 25%, 50%, 75%, and 100% 1RM was normalized to the amplitude during the left trunk rotation at 100% 1RM. The Vs of the OE was normalized to that of the OE during the left trunk rotation at 100% 1RM, and the Vs of the OI was normalized to that of the OI during the right trunk rotation at 100% 1RM. The EMG amplitude showed a significant correlation with the Vs of the OE during the left trunk rotation and the Vs of the OI during the right trunk rotation
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