Validation of functional calibration and strap-down joint drift correction for computing 3D joint angles of knee, hip, and trunk in alpine skiing

PLoS One

Pascal Schütz¹  Jörg Spörri²  Kamiar Aminian³  Silvio Lorenzetti³  Benedikt Fasel⁴ 

[1] Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland;Department of Sport Science and Kinesiology, University of Salzburg, Hallein-Rif, Austria;Institute for Biomechanics, Eidgenössische Technische Hochschule Zurich, Zurich Switzerland;Laboratory of Movement Analysis and Measurement, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

关键词: Knee joints;    Joints (anatomy);    Musculoskeletal system;    Hip;    Acceleration;    Knees;    Inertia;    Sports;   

DOI  :  10.1371/journal.pone.0181446

学科分类：医学（综合）

来源: Public Library of Science

【 摘 要 】

To obtain valid 3D joint angles with inertial sensors careful sensor-to-segment calibration (i.e. functional or anatomical calibration) is required and measured angular velocity at each sensor needs to be integrated to obtain segment and joint orientation (i.e. joint angles). Existing functional and anatomical calibration procedures were optimized for gait analysis and calibration movements were impractical to perform in outdoor settings. Thus, the aims of this study were 1) to propose and validate a set of calibration movements that were optimized for alpine skiing and could be performed outdoors and 2) to validate the 3D joint angles of the knee, hip, and trunk during alpine skiing. The proposed functional calibration movements consisted of squats, trunk rotations, hip ad/abductions, and upright standing. The joint drift correction previously proposed for alpine ski racing was improved by adding a second step to reduce separately azimuth drift. The system was validated indoors on a skiing carpet at the maximum belt speed of 21 km/h and for measurement durations of 120 seconds. Calibration repeatability was on average <2.7° (i.e. 3D joint angles changed on average <2.7° for two repeated sets of calibration movements) and all movements could be executed wearing ski-boots. Joint angle precision was <4.9° for all angles and accuracy ranged from -10.7° to 4.2° where the presence of an athlete-specific bias was observed especially for the flexion angle. The improved joint drift correction reduced azimuth drift from over 25° to less than 5°. In conclusion, the system was valid for measuring 3D joint angles during alpine skiing and could be used outdoors. Errors were similar to the values reported in other studies for gait. The system may be well suited for within-athlete analysis but care should be taken for between-athlete analysis because of a possible athlete-specific joint angle bias.

【 授权许可】

CC BY