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


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Riley
N A
NA
Physical Therapy and Rehabilitation Science, College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
Bilodeau
M
M
D000368:Aged; D000704:Analysis of Variance; D001132:Arm / Q000503:physiopathology*; D003627:Data Interpretation, Statistical; D004551:Elbow Joint / Q000294:innervation / Q000503:physiopathology; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008875:Middle Aged; D018763:Muscle Fatigue / Q000502:physiology*; D010243:Paralysis / Q000503:physiopathology; D020521:Stroke / Q000503:physiopathology*; D019415:Torque