Repeatability of electromyography normalization of the neck and shoulder muscles in symptomatic office workers

Purpose. The purpose of the study was to examine the repeatability of electromyography (EMG) normalization in office workers with neck and shoulder symptoms. Methods. Fifteen female office workers with neck/shoulder symptoms were recruited to participate in two separate days of testing. Maximum voluntary isometric contraction (MVIC) was used for the normalization of EMG data on the following muscles: cervical erector spinae, upper trapezius, lower trapezius and anterior deltoid. Repeatability was calculated using the intra-class correlation (ICC), relative standard error of measurement (%SEM) and relative coefficient of variation (%CV). Results. Peak root mean square (rms) and median frequency (MF) showed good to high repeatability in the UT, AD and CES (ICC=0.87-0.95, %SEM=2.65-9.48, %CV=0.2-5.9). The repeatability of peak rms was good (ICC=0.87, %SEM=12.56, %CV=3.3) and the MF of the LT was fair (ICC=0.76, %SEM=5.71, %CV=2.9). Conclusion. Peak rms and MF from the MVIC normalization method can be measured with sufficient repeatability in symptomatic office workers.