Abstract
A key point in human movement analysis is measuring the trajectory of a person’s center of mass (CoM). For outdoor applications, differential Global Navigation Satellite Systems (GNSS) can be used for tracking persons since they allow measuring the trajectory and speed of the GNSS antenna with centimeter accuracy. However, the antenna cannot be placed exactly at the person’s CoM, but rather on the head or upper back. Thus, a model is needed to relate the measured antenna trajectory to the CoM trajectory. In this paper we propose to estimate the person’s posture based on measurements obtained from inertial sensors. From this estimated posture the CoM is computed relative to the antenna position and finally fused with the GNSS trajectory information to obtain the absolute CoM trajectory. In a biomechanical field experiment, the method has been applied to alpine ski racing and validated against a camera-based stereo photogrammetric system. CoM position accuracy and precision was found to be 0.08 m and 0.04 m, respectively. CoM speed accuracy and precision was 0.04 m/s and 0.14 m/s, respectively. The observed accuracy and precision might be sufficient for measuring performance- or equipment-related trajectory differences in alpine ski racing. Moreover, the CoM estimation was not based on a movement-specific model and could be used for other skiing disciplines or sports as well.
Highlights
2016, 8, 671 wearable system fused the data from the dGNSS with the inertial sensor-based system to obtain as accurate and precise position and speed estimates of the center of mass (CoM) as possible
DGNSS and inertial sensors have been combined for obtaining an estimate of the center of mass kinematics for alpine ski racing
Inertial sensors were used to compute a full 3D body model of the skier. This model was fused with the position and speed data obtained from dGNSS and the skier’s CoM kinematics were calculated
Summary
In the sport of alpine ski racing, precise data of the center of mass (CoM) position, speed and acceleration are indispensable for the purposes of performance analysis and injury prevention [1,2,3,4,5,6,7,8,9].Early studies mainly used camera-based stereo photogrammetry to collect kinematic data on a ski-slope and to reconstruct the CoM kinematics [2,3,7,10,11,12,13]. In the sport of alpine ski racing, precise data of the center of mass (CoM) position, speed and acceleration are indispensable for the purposes of performance analysis and injury prevention [1,2,3,4,5,6,7,8,9]. Despite advantages in measurement accuracy, these systems are complex to set up and need for time-consuming post processing due to manual digitization. They are limited in capture volume, allowing the analysis of a short turn sequence only. One disadvantage of these systems is that the exact CoM position in space and time cannot be measured directly, as Remote Sens. One disadvantage of these systems is that the exact CoM position in space and time cannot be measured directly, as Remote Sens. 2016, 8, 671; doi:10.3390/rs8080671 www.mdpi.com/journal/remotesensing
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