This study aimed to evaluate the asymmetry in the lateral abdominal muscles (LAMs) expressed as tissue deformation index asymmetry (aTDI) with the use of M-mode ultrasonography. The muscles of interest were the transversus abdominis, internal oblique, and external oblique. This is a cohort of 126 healthy subjects who participated in the study. Measurements were taken by two raters, blinded to the aim of the study. M-mode ultrasounds with a measurement frequency of 5 MHz were utilized to record the postural response of LAMs to external perturbation in the form of rapid arm abduction with load, and individual aTDI values for each muscle were calculated. The aTDI values from deep to superficial LAMs were 78.28% for transversus abdominis, 55.68% for internal oblique, and 44.80% for external oblique. Only the aTDI for transversus abdominis results differed significantly from those of the other LAMs (P<0.05). LAM asymmetry values exhibit the following gradient: transversus abdominis >internal oblique >external oblique. Specifically, only transversus abdominis demonstrates noteworthy asymmetry in postural activity. This observation contributes to the literature by indicating that transversus abdominis asymmetry may serve as a marker for assessing the variability in motor control of the deep abdominal musculature. The dominance of transversus abdominis (TrA) asymmetric activity underlines the importance of personalized approaches for patients with lumbopelvic disorders or for athletes seeking to enhance performance.