The Effect of Lumbar Multifidus and Transversus Abdominis Muscle Activation on Balance in Patients with Hemiplegia

Background/Objectives: This study investigated whether ultrasonographically assessed contractility of the transversus abdominis (TrA) and lumbar multifidus muscles predicts balance and postural control in stroke-related hemiplegia. Methods: This cross-sectional study included 36 patients with subacute or chronic stroke. Balance was assessed using the Berg Balance Scale (BBS) and the Postural Assessment Scale for Stroke Patients (PASS). Bilateral L2-3, L3-4, and L4-5 multifidus and bilateral TrA muscle thickness were measured ultrasonographically at rest and during contraction. The thickening fraction (TF, %), resting thickness ratio (RTR, %), and TF ratio (TFR, %) were calculated. Significant correlates were entered into hierarchical regression models to identify independent predictors of balance. Results: The mean BBS was 39.92 ± 13.67, and the mean PASS-Total was 30.06 ± 4.59 (Maintaining a Posture [MP]: 10.65 ± 2.56; Changing a Posture [CP]: 19.41 ± 2.52). Moderate positive correlations were found between paretic-side L2-3 (pL2-3) multifidus TF and BBS and PASS-MP, while weak positive correlations were observed between paretic-side TrA TF and PASS-CP and between TrA TFR and BBS, PASS-Total, and PASS-CP. In hierarchical regression models, pL2-3 multifidus TF was a significant independent predictor of both BBS (ΔR² = 0.102, p = 0.020, β = 0.340) and PASS-MP (ΔR² = 0.090, p = 0.020, β = 0.320). Muscle parameters did not independently predict PASS-Total or PASS-CP. Conclusions: Paretic-side lumbar multifidus activation was identified as a significant independent predictor of balance and postural control, whereas TrA parameters did not independently predict balance outcomes in this population.