An acquisition system exploiting event-based approach applied to surface ElectroMyoGraphy (sEMG) was developed, with the goal of reducing the device size and minimizing the power consumption. The device has a modular four-channels architecture; each single acquisition module is characterized by a power consumption of 0.635 mW, a body area of 414 mm² and a weight of 2 g, making it a good fit for wearable applications. In-vivo experiments have been conducted on 11 subjects, during isometric contraction with increasing load of the Biceps Brachii and Vastus Lateralis muscles. The device was able to discriminate different muscular activation levels, through the average number (over time) of threshold-crossing events, providing promising results in terms of correlation with the weight (median values of 0.97 and 0.95 respectively), compared to standard sEMG parameters described in literature.