Standardization of Ex Vivo Myo-mechanical Assessment in the Rat Rectus Abdominis Muscle: Bilateral Analysis and Sex-Based Comparison to Advance Experimental Research

Abstract The fields of regenerative medicine and tissue engineering face challenges in developing affordable and reliable experimental models to study skeletal muscle regeneration and function. Although ex vivo myomechanical assessment (EMM) is a valuable tool, standardized protocols for small, flat, tendonless muscles such as the rat Rectus Abdominis Muscle (RAM) are lacking. This study aimed to develop and validate a standardized, affordable, and reproducible EMM protocol to assess the functional and myo-mechanical properties of the RAM. The methodology involved harvesting the RAM from 7 female and 10 male Sprague Dawley rats and analyzing contractile responses to electrical stimulation. Key parameters measured included Time to Peak (TTP), Rate of Force Development (RFD), and Half-Relaxation Time (HRT). Results revealed sexual dimorphism in body weight and muscle characteristics. Females showed longer TTP and significantly shorter HRT compared to males, who exhibited markedly slower relaxation properties (p < 0.001). Furthermore, Spearman correlation analysis revealed that distinct morphological factors predict muscle function across sexes. The findings highlight sex and side-specific patterns in RAM responsiveness and validate a robust protocol. This standardized EMM technique provides a reliable and reproducible method for evaluating RAM behavior, contributing significantly to preclinical research in regenerative medicine and tissue engineering.