Deep Trunk Muscle Activation and Balance in Post-Stroke Hemiplegia

Trunk muscle dysfunction in stroke patients leads to both balance impairments and excessive compensatory effort to maintain postural control. While some patients completely lose their ambulation ability due to stroke, others experience increased postural sway and impaired balance, which elevate the fear and risk of falling. Previous studies have demonstrated a significant relationship between static balance, duration of hospital stay, and post-stroke functional abilities. Furthermore, early-stage trunk muscle control has been shown to be a strong predictor of activities of daily living within the first six months post-stroke. Although numerous studies have proven the efficacy of core stabilization exercises on balance and functional outcomes in hemiplegic patients, data on individual deep muscle dynamics remain limited.

Therefore, this cross-sectional study aimed to investigate the relationship between ultrasound-measured bilateral transversus abdominis and bilateral lumbar multifidus muscle values and balance performance in patients with hemiplegia. The study population consists of adult patients diagnosed with post-stroke hemiplegia who underwent clinical and ultrasonographic evaluations. Participants are selected from patients receiving inpatient or outpatient rehabilitation at a single tertiary training and research hospital, according to specific functional and clinical eligibility criteria using a non-probability convenience sampling method.

To standardize the ultrasonographic measurements and minimize inter-individual variations, specific muscle parameters are calculated and integrated into the statistical analyses:

Paretic Thickening Fraction (TF) = ([Contraction Thickness - Resting Thickness] / Resting Thickness) x 100,

Resting Thickness Ratio (RTR) = (Paretic Resting Thickness / Non-paretic Resting Thickness) x 100,

Thickening Fraction Ratio (TFR) = (Paretic Thickening Fraction / Non-paretic Thickening Fraction) x 100.

Statistical analyses will be performed to evaluate the relationships between these muscle parameters and clinical balance scores. Initially, correlation analyses will be performed between the dependent and independent variables to identify potential predictors. Subsequently, hierarchical linear regression analyses will be conducted to evaluate the specific impact of muscle values on balance outcomes. In these models, confounding control variables will be entered in the first block (Block 1) to adjust for baseline characteristics. The muscle parameters that demonstrated significant correlations in the initial analysis will be entered in the second block (Block 2). This hierarchical approach will allow for the determination of the incremental variance explained by deep trunk muscle dynamics on postural balance performance, over and above the control variables. A p-value of less than 0.05 will be considered statistically significant.

Inclusion criteria

• Age 18-65 years
• At least 1 month post stroke
• History of unilateral stroke
• Ability to cooperate cognitively
• Ability to maintain balance while sitting without support and/or balance while standing with or without support
• BMI < 30 kg/m²

Exclusion criteria

• History of hemiplegia on the opposite side of the body
• Diagnosis of extruded or sequestrated lumbar herniation and/or a history of lumbar surgery
• History of lumbar vertebral fracture
• Traumatic brain injury
• Neuromuscular disorders that may cause muscle atrophy
• Sensory deficits
• Cerebellar sequelae
• Vestibular balance disorders (e.g., vertigo)
• Parkinson's disease
• Balance impairments due to visual deficits
• Pre-stroke balance disorders