Changes in upper limb joint torque patterns and EMG signals with fatigue following a stroke

• Published in: Disability and rehabilitation Vol. 24; no. 18; p. 961
• Main Authors: Riley, N A, Bilodeau, M
• Format: Journal Article
• Language: English
• Published: England 15.12.2002
• Subjects: Aged; Analysis of Variance; Arm - physiopathology; Data Interpretation, Statistical; Elbow Joint - innervation; Elbow Joint - physiopathology; Electromyography; Female; Humans; Isometric Contraction - physiology; Male; Middle Aged; Muscle Fatigue - physiology; Paralysis - physiopathology; Stroke - physiopathology; Torque
• ISSN: 0963-8288
• DOI: 10.1080/0963828021000007932

Little is known concerning changes in neuromuscular fatigue following a stroke. The purpose of this study was to evaluate the effect of a stroke on fatigue-related changes in upper limb torque patterns and electromyographic signals. The paretic and non-paretic upper limb of 10 adults (51-79 years) who had a stroke (time since stroke: 3-75 months) were compared. Subjects had to perform a fatigue task consisting of a sustained maximal isometric contraction in elbow flexion until torque decreased to below 50% of initial. The main variables of interest assessed before, during and after fatigue were: (1) the torque in elbow flexion, as well as associated forces/torques at the shoulder and forearm; (2) the level of voluntary activation; (3) the amplitude (RMS); and (4) frequency content (median frequency) of electromyographic signals. Compared to the non-paretic side, the paretic side showed a lower level of voluntary activation and higher relative torque levels at the forearm and shoulder which could both be exaggerated with fatigue, and a lesser fatigue-related decrease in median frequency. Thus, greater fatigue-related changes in features of the central command (ability to maximally activate a muscle and ability to isolate effort to a muscle group) were observed for the paretic compared with the non-paretic side. This could be a confounding factor when assessing changes in peripheral measures of fatigue following a stroke using voluntary contractions.