||We implemented and tested a wearable sensor system to measure patterns of stress responses of a professional musician under public performance conditions. Using this sensor system, we monitored the cellist’s heart activity, the motion of multiple body parts, and their gradual changes during three repeated performances of a skill-demanding piece in front of a professional audience. From the cellist and her teachers, we collected stage fright self-reports and performance ratings that were related to our sensor data analysis results. Concomitantly to changes in body motion and HR, the cellist perceived a reduction in stage fright. Performance quality was objectively improved, as technical playing errors decreased throughout repeated renditions. In particular from performance 1 to 3, the wearable sensors measured a significant increase in the cellist’s bowing motion dynamics of \sim6% and a decrease in heart rate (HR). Bowing motion showed a marginal correlation to the observed HR patterns during playing. The wearable system did not interfere with the cellist’s performance, thereby allowing investigation of stress responses during natural public performances.