Architectural analysis of human abdominal wall muscles: Implications for mechanical function

Study Design. Cadaveric analysis of human abdominal muscle architecture. Objective. To quantify the architectural properties of rectus abdominis (RA), external oblique (EO), internal oblique (IO), and transverse abdominis (TrA), and model mechanical function in light of these new data. Summary of Background Data. Knowledge of muscle architecture provides the structural basis for predicting muscle function. Abdominal muscles greatly affect spine loading, stability, injury prevention, and rehabilitation; however, their architectural properties are unknown. Methods. Abdominal muscles from 11 elderly human cadavers were removed intact, separated into regions, and microdissected for quantification of physiologic cross-sectional area, fascicle length and sarcomere length. From these data, sarcomere operating length ranges were calculated. Results. IO had the largest physiologic cross-sectional area and RA the smallest, and would thus generate the largest and smallest isometric forces, respectively. RA had the longest fascicle length followed by EO, and would thus be capable of generating force over the widest range of lengths. Measured sarcomere lengths, in the postmortem neutral spine posture, were significantly longer in RA and EO (3.29 ± 0.07 and 3.18 ± 0.11 μm) compared to IO and TrA (2.61 ± 0.06 and 2.58 ± 0.05 μm) (P < 0.0001). Biomechanical modeling predicted that RA, EO and TrA act at optimal forcegenerating length in the midrange of lumbar spine flexion, where IO can generate approximately 90% of its maximum force. Conclusion. These data provide clinically relevant insights into the ability of the abdominal wall muscles to generate force and change length throughout the lumbar spine range of motion. This will impact the understanding of potential postures in which the forcegenerating and spine stabilizing ability of these muscles become compromised, which can guide exercise/rehabilitation develop ment and prescription. Future work should explore the mechanical interactions among these muscles and their relationship to spine health and function.