Long term reliability of EMG measurements in adults with cystic fibrosis

The aim of this study was to investigate the long term reliability of surface electromyography (sEMG) measurements in adults with cystic fibrosis (CF). Eighteen healthy subjects (CO) and sixteen adults with CF were tested on two occasions, six weeks apart. sEMG was recorded from the rectus femoris, vastus lateralis and vastus medialis obliquus muscles during maximal voluntary contraction (MVC) and 50% MVC until exhaustion. Quadriceps muscle activity during 50% MVC was described using four measures (initial, final, normalized and slope values) for both frequency and time domain. Relative (ICC) and absolute (SEM) reliabilities were applied to asses test-retest reliability. In CF group, median frequency (MDF) values for 100% MVC and initial, final and normalized final MDF for 50% MVC demonstrated moderate to very high relative reliability (ICC = 0.60–0.91) and low variability (SEM = 5.5–13%). MDF slope showed large variability in both groups. Root mean square (RMS) values were not reproducible in both groups whatever the intensity of exercise and can not be recommended as outcomes parameters. In conclusion, sEMG measurements during maximal and submaximal isometric contractions could be valid and reliable tools for clinical applications in cystic fibrosis patients but mainly in the frequency domain and from rectus femoris.