Marker-Based Method for Analyzing the Three-Dimensional Upper Body Kinematics of Violinists: Reproducibility.

Background: Recently, Wolf et al. proposed a novel, marker-based method to analyze the three-dimensional upper-body kinematics of high string players for clinical application. The method provides an objective evaluation of high string players' motor strategies, especially in the shoulder complex, by distinguishing between the scapulothoracic (ST) and glenohumeral (GH) joints, while minimizing skin movement artifacts, marker occlusions, and limitations due to instrument placement. Nevertheless, reproducibility of kinematic measurements is crucial for clinical applications. The aim of this study was to assess the method's reproducibility in terms of reliability and repeatability.

Methods: One healthy professional violinist underwent a total of nine bowing trials in three different laboratory sessions. Each trial was conducted by one of two different examiners. A biomechanical model was applied to motion capture data of the pelvis, thorax, spine, and head, as well as both upper limbs (consisting of the scapula, upper arm, forearm and hand). Reproducibility was assessed by calculating inter- and intra-tester, inter-session, and intra-subject measurement errors for each rotational degree of freedom in the upper-body segments and joints.

Findings: Small measurement errors were accepted to be good indicators for reproducibility. Intra- and inter-tester errors were found to be small (< 3° for the most part). Both inter-session and intra-subject repeatability were found to be larger (< 5° for the most part).

Interpretation: This study generally showed the novel, marker-based method to have good reproducibility for a healthy violinist. This indicates that the proposed method is a reliable tool for quantifying upper-body movements during violin playing across subjects, examiners, laboratories, and motion capture systems.