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Abstract
The aim of the study was to investigate short-term, intermediate-term and long-term
reliability of surface electromyographic (EMG) measurements.
Eighteen healthy subjects performed 810 isometric knee extension tests. Reliability
for maximum voluntary contraction (MVC) and 50% MVC was assessed with retest intervals
of 3 min, 90 min and 6 weeks. Reliability for sustained contractions was assessed
with retest intervals of 90 min and 6 weeks. EMG was recorded from the rectus femoris,
vastus lateralis and vastus medialis muscles. The root mean square (RMS) and the median
frequency (MF) parameters were extracted. At sustained contraction tasks, estimated
linear regression values of both parameters were analyzed. Bland-Altman-plots, coefficient
of repeatability, Pearson's coefficient of correlation and intra class correlation
(ICC) procedures were applied to assess test-retest reliability.
EMG recordings taken at short-term intervals were generally better reproducible than
those of the longer-term intervals. Moreover, 50% MVC EMG recordings demonstrated
better reproducibility than 100% MVC measurements, and EMG recorded from the rectus
femoris were more constant than that from the vastus lateralis or vastus medialis.
The MF parameter recorded from the rectus femoris was the only reliable parameter
of EMG fatigue change.
In our set up, EMG measurement is best suited for clinical applications if submaximal
MVC measurements are performed and signal is taken from rectus femoris muscle.