Application of Ultrasonography in the Assessment of Abdominal and Lumbar Trunk Muscle Activity in Participants With and Without Low Back Pain: A Systematic Review

Objective: The purpose of this study was to systematically review the literature regarding which condition (task, position, or contraction type), changes in muscle thickness could be interpreted as muscle activity of trunk muscles. Methods: Studies that assessed the correlation between changes in muscle thickness measured with ultrasonography (US) and electromyography (EMG) activity were included. Only the data related to abdominal and lumbar trunk muscles in participants with or without low back pain were extracted. The PubMed, ScienceDirect, Ovid MEDLINE, Scopus, Springer, and Cumulative Index to Nursing and Allied Health Literature databases were searched from inception to August 2018. Two independent raters appraised the quality of the included studies using the Critical Appraisal Skills Program checklist. Results: Fourteen studies were included. The results revealed significant correlations between US and EMG measures for the lumbar multifidus and erector spinae muscle during most contraction levels and postures. For transverse abdominis and internal oblique, US and EMG measures were correlated during low load abdominal drawing or bracing. The correlations were influenced by trunk position for higher intensities of contraction. For the external oblique muscle, correlation was observed only during trunk rotation. Conclusion: Changes in muscle thickness should not be interpreted as muscle activity for all tasks, positions. and contraction types. Only during prime movement tasks performed with isometric contraction could muscle thickness change be considered as muscle activity. Also, upright postures influenced the relationship between changes in muscle thickness and muscle activity for abdominal muscles.