Impaired Firing Behavior of Individually Tracked Paretic Motor Units During Fatiguing Contractions of the Dorsiflexors and Functional Implications Post Stroke
Francesco Negro, Kathleen E. Bathon, Jennifer Nguyen, Cassidy G. Bannon, Claudio Orizio, Sandra K. Hunter, Allison S. Hyngstrom
Abstract
Introduction: This study quantified stroke-related changes in:1) the averaged discharge rate of motor units (individually tracked and untracked) identified from HD-EMG recordings, 2) global muscle EMG properties of the dorsiflexors during a fatiguing contraction and 3) relate task endurance to measures of leg function. Methods: Ten individuals with chronic stroke performed a sustained sub-maximal, isometric, fatiguing dorsiflexion contraction in paretic and non-paretic legs. Motor-unit firing behavior, task duration, maximal voluntary contraction strength (MVC), and clinical measures of leg function were obtained. Results: Compared to the non-paretic leg, paretic task duration was shorter and there was a larger exercise-related reduction in motor unit global rates, individually tracked discharge rates, and overall magnitude of EMG. Task duration of the paretic leg was more predictive of walking speed and lower extremity Fugl-Meyer scores compared to the non-paretic leg. Discussion: Paretic muscle fatigability is increased post stroke and is characterized by impaired rate coding and recruitment and is functionally relevant.