FUNCTIONAL SUBDIVISION OF THE UPPER TRAPEZIUS MUSCLE DURING LOW-LEVELACTIVATION

The electromyographic (EMG) amplitude was recorded using bipolar surfa ce electrodes placed at different positions above the upper trapezius muscle of 16 healthy subjects. One of the aims of this study was to in vestigate the Variation in EMG activity between electrode positions. F or this purpose three tasks were performed: a mental activation test, a dynamic movement test and 90 degrees arm abduction. The EMG signals were full-wave rectified and averaged within windows that were 0.2 s i n length. Normalized EMG activity showed significantly different EMG a mplitudes at different electrode positions for two of the three tasks. The second aim of this study was to investigate whether the upper tra pezius muscle may be functionally subdivided. For this purpose the nor malized EMG amplitudes of each task were compared with the EMG amplitu de recorded during submaximal shoulder elevation. While the EMG level was similar at one electrode position, significant differences were fo und at some of the other electrode positions, indicating a functional subdivision of the muscle. The present results indicate that for compa risons of upper trapezius EMG activity levels between some tasks or be tween subjects, it is worthwhile to make EMG recordings at several ele ctrode positions.