Muscle activity can be assessed non-invasively by means of surface electrodes places at the skin overlyin a muscle. When multiy-channel array electrodes are used, it is possible to extract motor unit action potentials (MUAP's) from the EMG signals with a segmentation approach based on the Continuous Wavelet Transform... The objective of the present study was to determine the test-retest reliability of the mentioned parameters during different tasks of the shoulder and neck muscles