Impact of resting muscle tone and stiffness in acute stroke survivors: which muscles' tone correlates with trunk control? a cross-sectional study.

BACKGROUND Trunk control is an early predictor of functional and motor recovery in acute ischemic stroke (AIS). Although changes in muscle tone and stiffness post-stroke are well documented, their relationship with trunk control remains underexplored.

OBJECTIVE To identify which trunk muscles' resting tone and stiffness are most strongly correlated with trunk control in AIS survivors.

METHODS Thirty AIS survivors (time from symptom onset ≤72 hours) were included in this cross-sectional study. Trunk control and global disability were assessed using the Trunk Impairment Scale (TIS) and modified Rankin Scale (mRS), respectively. MyotonPRO® was used to measure tone and stiffness of the Longissimus Thoracis (LT), Lumbar Multifidus (LM), Trapezius (T), and Rectus Femoris (RF) muscles. Pearson's correlation and multiple linear regression analyses were performed.

RESULTS TIS scores correlated strongly with LT tone (r = 0.604, p < 0.001), LT stiffness (r = 0.648, p < 0.001), and LM stiffness (r = 0.619, p < 0.001), and moderately with LM tone (r = 0.410, p = 0.012), but not with Trapezius tone (p = 0.092) or RF stiffness (p = 0.305). LT stiffness showed a strong negative correlation with mRS grade (r = -0.648, p < 0.001). Regression analysis identified LT tone (R2 = 0.318, p = 0.008) and LT stiffness (R2 = 0.432, p = 0.001) as significant independent predictors of trunk control.

CONCLUSIONS Resting tone and stiffness of the LT are associated with trunk control and global disability in AIS survivors. Higher LT stiffness predicts better trunk control and lower disability, suggesting its potential as an early marker of functional recovery.

TRIAL REGISTRATION Clinicaltrials.gov (NCT06006988).