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.