Subacromial pain syndrome (SPS) is a common cause of shoulder pain and muscle activity deficits are postulated to contribute to the development and progression of the disorder. The purpose of this systematic review was to definitively determine whether evidence exists of differences in electromyography (EMG) characteristics between subjects with and without SPS.Six key databases were searched: MEDLINE, EMBASE, CINAHL, SPORTdiscus, PEDro and The Cochrane Library (inception to May 2016). The search yielded 1414 records using terms relating to shoulder impingement, EMG, scapular and rotator cuff muscles. Twenty-two papers remained once duplicates were removed and selection criteria applied. Data extraction, quality assessment and data synthesis were performed. Effect sizes and 95% confidence intervals were calculated.There was limited evidence that serratus anterior has lower amplitude, delayed activation and earlier termination in SPS participants. For the majority of muscles, regardless of task, load or arm position, significant differences were not demonstrated or results were contradictory.The understanding of SPS is changing and EMG appears unable to capture the complexities associated with this condition. Addressing aberrant movement patterns and facilitating balanced activation of all shoulder muscles may be a more appropriate treatment direction for the future.