Could changes in the ultrasound image of the muscles of the lateral abdominal wall be seen as a sign of muscle activity? A narrative review

Aim. Currently, ultrasonography (USG) is used to study changes occurring in the lateral abdominal wall muscles (LAM). Here, the question that naturally arises is whether a change in the thickness of the ultrasound image can be identified with a change in muscle activity. Therefore, the purpose of the present work is to: 1) undertake an analysis of available publications exploring the relationship between electromyography (EMG) and USG; 2) define the USG measurement of each LAM; 3) identify gaps in the literature. Material and methods. The databases MEDLINE, POL-index and Google Scholar were used to search the literature. We used a combination of terms (in Polish and English) containing the abbreviated and full names of the following expressions: ultrasound, electromyography and external oblique muscle, internal oblique muscle, or transverse abdominal muscle. Results. Nine publications fulfilled the conditions for inclusion in the analysis. These used different methodologies and test conditions, making it difficult to interpret the results of individual works. The majority demonstrated poor or no correlation between EMG and USG measurements. Conclusion. Changes in the thickness of the LAM using USG should not be equated with a change in muscle activity. To avoid misinterpretation, one should avoid the term “muscle activity” in evaluating changes in the thickness of the LAM. It is recommended that the terms “thickness change” or “morphological change” be used in the assessment of this phenomenon, which is closely related to real changes in USG imaging, expressing a more complex phenomenon than a mere change in bioelectrical potential.