Innovative stimulated muscle contraction signals based digital muscle marker: a reliable tool for assessing muscle in persons with stroke.

BACKGROUND: Stroke leads to motor dysfunction as a result of damage to the central nervous system, often resulting in secondary muscle changes from disuse and immobilization. Existing tools for assessing these muscle changes in persons with stroke are limited, as these methods rely on voluntary muscle contractions, which are frequently impaired in hemiparesis. Additionally, these assessments often require complex and cumbersome equipment. Therefore, a novel system that can address these issues, with high levels of reliability is needed. This study introduces and evaluates the reliability levels of a novel technique using stimulated muscle contraction signals (SMCS)-based digital muscle markers. METHODS: SMCS-based digital muscle markers were measured on both thighs of participants with hemiplegic stroke (n = 40). Three trials were conducted by two examiners using the exoPill device, which captures muscle contraction signals induced by electrical stimulation. Isometric knee extensor strength and hand grip strength were measured, and appendicular lean mass was estimated using bioelectrical impedance analysis. The intra- and inter-rater reliability of SMCS-based digital muscle marker measurements was evaluated using the intraclass correlation coefficient (ICC), coefficient of variance (CV), and 95% limits of agreement (LOA). RESULTS: The ICC for both intra- and inter-rater reliability of SMCS-based digital muscle marker measurements exceeded 0.98 on both the affected and unaffected sides. The CV was consistently low, ranging from 1.36% to 3.07% in the unaffected leg, and remained under 3% in the affected leg. Bland-Altman plots confirmed consistent agreement, with most measurements falling within the 95% LOA and no systematic bias were observed. Mean differences for intra- and inter-rater assessments ranged from - 0.43 to 0.25 for the unaffected leg and from 0.00 to 0.05 for the affected leg. Spearman correlation coefficient showed moderate to good correlation (ρ = 0.50) between SMCS-based digital muscle markers and knee extensor strength for both unaffected and affected leg, and good to excellent correlations (ρ = 0.87) between SMCS-based digital muscle markers and leg lean mass. CONCLUSIONS: SMCS-based digital muscle markers demonstrated high reliability and significant correlations with muscle strength and mass, suggesting their potential utility for assessing muscle in individuals with stroke.