Elevated Forearm Coactivation Levels and Higher Temporal Variability in String Players with Musicians' Dystonia During Demanding Playing Conditions.

Abstract

There is a lack of an objective measurement tool for evaluating the quality of bowing performance in string players. The present study aimed to assess kinematic features of bow strokes performed by violinists and violists affected by bow arm dystonia, compared to healthy controls. Seven musicians with musician's dystonia and 20 healthy controls participated in the study. A 3D motion capture system was used to record repetitive bowing on a single string at fixed velocities. Temporal variability, an indirect indicator for motor disturbances, was computed in order to evaluate the musicians' performance during the repetitive movements. Simultaneously, muscular activity of essential flexors and extensors of the right arm was recorded using surface electromyography. Antagonistic muscular coactivation and temporal variability were analyzed in a multilevel linear model framework. The results revealed generally higher forearm coactivation during upstrokes as compared to downstrokes in both groups. Whereas coactivation levels of the upper arm did not significantly differ between groups, we found increased forearm coactivation in patients during the more demanding playing conditions. Increased coactivation may represent an adaptive motor control strategy that is applied in order to reduce noise entering the motor system. Furthermore, affected musicians executed bow strokes with higher temporal variability than healthy controls, especially during fast playing. Building on these results we introduce a novel approach using simple kinematic measures to quantifying dystonic symptoms in string players. Even though dystonia patients showed higher temporal variability and elevated forearm coactivation, both variables were not correlated. This finding is discussed with respect to the heterogeneity of musicians' dystonia and its individual-specific manifestations in dystonic symptoms.