Introduction: This is a research study, supported by a literature review, which gave the principles of anatomy, biomechanics, physiological and patological conditions of shoulder functioning. Correct muscle activity is essential for proper functioning of the shoulder. Electromyography is a method which enables to record and analize the signs of muscle activity. This tool is useful for veryfing the manual muscle tests, typically used for clinical examination of the shoulder. The aim of this study was to investigate electric activation of 8 shoulder muscles while manual testing the resistive external rotation in scapulohumeral joint. Material and methods: Fourteen healthy subjects (n=14) were manually tested for isometric resistance. Three tests were used, each with different level of abduction, respectively: the m. infraspinatus test (1): 0 degrees, non-specific biceps brachii tendon test (2): 45 degrees, resistive test for external rotation in the position of maximal internal rotation (3): 90 degrees. The superficial electromyography device used in the study was Noraxon: TeleMyo System 2400T, with MyoResearch XP software. It collected data about the muscle electric activity during all the tests. Statistic data mining was made using Statistica programme. Peak amplitude values were collected and comparison of three tests was made. Results: High supraspinatus activation could be observed together with high coactivation of other shoulder muscles. Also, inter-individual dispersion of muscle activation values was high. Conclusions: Surface electromyography alone appeared to be insufficient method for assesing manual muscle tests, although it may give suggestions for testing and therapeutic exercises. Results of electromyography need to be confirmed by conducting large group studies, and large scatter of muscle activation values has to be taken account.