Reliability of the kinematic theory parameters during handwriting tasks on a vertical setup

Background: The Kinematic Theory and its Sigma-Lognormal model have been used extensively in motor control analyses. It has recently shown promise in its ability to detect neuromuscular fatigue in the shoulder. The use of an ergonomic setup composed of a vertically oriented tablet offers a good demonstration for use in future clinical applications. However, parameters' reliability of this theory needs to be evaluated. The aim of this study is to assess the test-retest reliability of these parameters in the specific case of fatigue detection. Method: Forty participants performed two sessions of fast strokes handwriting (simple strokes, triangles, horizontal and vertical oscillations) on a tablet placed at shoulder's height. Reliability was assessed using the intraclass correlation coefficient (ICC), their relative standard error of measurement (SEM) and coefficient of variation. The minimal detectable change was also reported. Findings: In general, a moderate to excellent reliability was denoted in the main parameters of each test (ICC: 0.54-0.91). The parameters related to shoulder fatigue detection had good to excellent reliability (ICC: 0.77-0.90) with low SEM (SEM: 4.75-6.99%). Conclusion: Most of the parameters have good test-retest reliability, and the setup seems adequate for shoulder fatigue detection.