FATIGUE-RELATED CHANGES IN SELECTED FEATURES OF VOLUNTARY MOTOR OUTPUT FOLLOWING A STROKE

Eichelberger T, Williams D, Bilodeau M.

Graduate Program in Physical Therapy and Rehabilitation Science, University of Iowa,

         Iowa City, Iowa.  Project funded by the American Heart Association,

(Heartland Affiliate, Grant 0160426Z).

martin-bilodeau@uiowa.edu

PURPOSE: The purpose of this study is to compare, between healthy controls and individuals who had a stroke, fatigue-related changes in motor output characteristics related to the ability to activate muscles.  The characteristics of interest are: 1) the extent of voluntary activation and

2) the specificity of the motor command.  The extent of voluntary activation refers to the capacity to maximally activate a muscle, whereas the specificity of the motor command refers to the ability to voluntarily activate a muscle or muscle group (e.g., elbow flexors) in isolation.  SUBJECTS: Eleven healthy volunteers and eight individuals with a stroke have presently been tested.  MATERIALS AND METHODS: Electromyographic signals of seven muscles, as well as forces and torques generated around the elbow and shoulder were measured during maximal elbow flexion efforts and during a fatigue task, which consisted of a maximal isometric elbow flexion contraction sustained until force decreased below 50% of initial.  DATA ANALYSIS: The extent of voluntary activation was assessed by superimposing a supramaximal train of electrical stimulation to the biceps brachii muscle during the maximal elbow flexion efforts and quantifying the extra force produced by the electrical stimulation above the voluntary force (with the absence of measured extra force reflecting a fully activated muscle).  The specificity of the motor command was assessed by quantifying the magnitude of forces and torques at the shoulder (abduction/adduction, internal/external rotation, horizontal abduction/adduction) and elbow (prono-supination) in directions other than elbow flexion.  Differences/changes in voluntary activation and specificity of the motor command between sides (right versus left in controls or paretic versus non-paretic in stroke) or groups (controls versus stroke) and with fatigue, were evaluated with mixed-design two way ANOVAs.  SUMMARY DATA/RESULTS: Preliminary analysis of data from the eight individuals with a stroke shows a reduced ability to maximally activate muscles on the paretic compared to the non-paretic side, which is exaggerated with sustained activity (fatigue).  In addition, forces/torques in directions other than that required by the main task can also be exaggerated with sustained activity on the paretic compared to the non-paretic side.  CONCLUSION: Our data suggest that certain impairments in motor control following a stroke could be exaggerated with fatigue.  CLINICAL RELEVANCE: This study will increase our understanding of the effect of fatigue on the ability of individuals who had a stroke to perform specific motor tasks, which in turn, could help in the design of optimal interventions for this population.

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