Improvising on the piano keyboard requires extensive skill development, which may reduce the feeling of immersion and flow for amateur players. However, being able to add simple musical effects greatly boosts a player’s ability to express their unique playing style. To simplify this process, we designed an electromyography-based (EMG) system which integrates seamlessly into normal play by allowing musicians to modulate sound pitch using their thumb. We conducted an exploratory user study where users played a predefined melody and improvised using our system and a standard pitch wheel. Interview responses and survey answers showed that the EMG-based system supported the players’ musical flow. Additionally, interviews indicated the system’s capabilities to foster player creativity, and that players enjoyed experimenting with the effect. Our work illustrates how EMG can support seamless integration into existing systems to extend the range of interactions provided by a given interface.