Sex-Based Differences in Tensiomyography as Assessed in the Lower Erector Spinae of Healthy Participants: An Observational Study

Background: Although there is mounting evidence on sex-linked differences in paraspinal muscle function, it is unknown whether sex-based variations in mechanical and contractile characteristics of the lumbar erector spinae (LES) can be monitored noninvasively in healthy participants at rest using tensiomyography (TMG). Hypothesis: Sex-specific effects in muscle displacement (Dm) and velocity of muscle deformation (Vd) will be observed via TMG assessed in the LES. Study Design: Observational study. Level of Evidence: Level 3. Methods: LES response was measured in a relaxed state in 40 healthy adults (20 females). Possible differences between the conditions were investigated using mixed-model analyses of variance. Two-stage hierarchical linear regression analyses were performed to predict the outcome of TMG Dm and Vd based on participant sex. Results: There were significant main effects of sex with large effect sizes for both TMG parameters, resulting from lower mean values in women compared with men (Dm, P < 0.01; Vd, P < 0.01). In contrast, neither the main effect of side (left vs right LES) nor the interaction between the side and sex reached significance (all P > 0.3). Introducing the sex variable in stage 2 of the regression analyses significantly improved the prediction of the TMG parameters (all increment R-2 >= 0.18; all P < 0.01; all f(2) >= 0.29). Conclusion: Sex-based differences in muscle stiffness and contractile characteristics could be observed by TMG on LES muscles in healthy individuals at rest. The data suggest that these disparities are not exclusively attributable to anthropometric measures but may be linked to intrinsic sex-based differences in skeletal muscle characteristics. Clinical Relevance: We recommend implementing TMG in a clinical setting using the obtained results as a basis to factor for the patient's biological sex when assessing effects of therapeutic/exercise regimens aiming at the optimization of myofascial tissue regeneration and performance.