Surface electromyography (sEMG) allows to evaluate neurophysiological aspects of movements. The traditional muscle-specific sEMG approach requires considerable expertise to correctly position bipolar derivations over each muscle of interest. This reduces the availability of myoelectric imaging tools for non-professional users in everyday life conditions. High-density EMG (HDsEMG) consists of recording the sEMG via a dense array of electrodes that restricts the imaging surface to a narrow area, thus limiting usability. Here we demonstrate the usability and advantages of a medium-density sEMG (MDsEMG). We recorded the muscle activity of a subject performing repeated arm flexion and extension using both muscle-specific sEMG (4 derivations over the biceps and triceps) and MDsEMG (28 monopolar derivations, positioned around the arm circumference). Grand-average dynamic-time-warped amplitudes showed similar activation patterns for both modalities. However, MDsEMG allowed to extract maps reflecting the spatial activation of muscles at different movement phases (minimum and maximum acceleration). MDsEMG also proved superior in decoding the elbow angle and allowed to map the regions of maximum significance. MDsEMG is a viable alternative to muscle-specific and HD sEMG. It does not require expertise in electrode positioning and is able to cover large surfaces. It thus can pave the way to easier myoelectric imaging in everyday life and more effective rehabilitation treatments.