Unilateral alterations in lower extremity intramuscular blood flow and morphology and their association with balance, gait speed and motor impairment in individuals with chronic stroke: A theoretical model

Background & Purpose: Impaired motor function, gait and balance may increase fall proclivity and fracture risk post-stroke. A theoretical model was developed to examine the association between unilateral alterations in paretic lower limb muscle and clinical assessments of post-stroke impairment using data collected from 64 individuals with chronic stroke.

Methods: Paretic intramuscular blood perfusion (vascularity index [VI]), echo intensity (EI), and segmental composition analysis (SLA) were assessed using ultrasound and bioelectrical impedance, respectively. Isometric peak torque (IPT), brief-BEST, 10-meter-walk-test (10MWT), and Fugl-Meyer (FMA) assessments were used to measure strength (plantarflexion), balance, gait speed and motor function, respectively. Path analyses were conducted to explore relationships between exogenous muscle (VI, EI, SLA) and endogenous functional factors (IPT, Brief-BEST, 10MWT, FMA).

Results: IPT was a significant predictor of Brief-BEST (R2=0.417), 10MWT (R2=0.406) and FMA (R2=0.243). VI, EI, and SLA-%fat were IPT correlates (r=-0.376-0.384). Path analyses indicated comparably better fit for Model 1 [DV=Brief-BEST, χ2(df)=0.589(3), probability=0.899, CFI=1.000, RMSEA=0.000], than Model 2 [DV=10MWT, χ2(df)=4.585(3), probability=0.205, CFI=0.967, RMSEA=0.087] and Model 3 [DV=FMA, χ2(df)=7.978(3), probability=0.046, CFI=0.893, RMSEA=0.115].

Conclusion: Reduced muscle blood perfusion (VI), and compositional changes (EI, SLA-%Fat) in paretic lower limbs demonstrated a relatively larger indirect effect on balance (Model 1), than gait speed (Model 2) and motor function (Model 3), which were moderated by their direct effects on muscle weakness (IPT). These models suggest that in addition to resistance training for improving strength, exercises which increase localized blood flow and enhance cardiometabolic health may also be important in remediating balance, and possibly motor and/or gait, deficits post-stroke.