Reliability of surface electromyographic measurements

Objectives: The aim of the study was to investigate short-term, intermediat e-term and long-term reliability of surface electromyographic (EMG) measure ments. Methods: Eighteen healthy subjects performed 810 isometric knee extension t ests. Reliability for maximum voluntary contraction (MVC) and 50% MVC was a ssessed 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 vastu s medialis muscles. The root mean square (RMS) and the median frequency (MF ) parameters were extracted. At sustained contraction tasks, estimated line ar regression values of both parameters were analyzed. Bland-Altman-plots, coefficient of repeatability, Pearson's coefficient of correlation and intr a class correlation (ICC) procedures were applied to assess test-retest rel iability. Results: EMG recordings taken at short-term intervals were generally better reproducible than those of the longer-term intervals. Moreover, 50% MVC EM G recordings demonstrated better reproducibility than 100% MVC measurements , and EMG recorded from the rectus femoris were more constant than that fro m the vastus lateralis or vastus medialis. The MF parameter recorded from t he rectus femoris was the only reliable parameter of EMG fatigue change. Conclusion: In our set up, EMG measurement is best suited for clinical appl ications if submaximal MVC measurements are performed and signal is taken f rom rectus femoris muscle. (C) 1999 Elsevier Science Ireland Ltd. All right s reserved.