Evaluating Inertial Motion Capture Systems for Sports Performance Analysis: A Case Study in the Measurement of Road Cycling Kinematics

摘要

Recent advances in the production of micro-electromechanical systems have led to the development of inertial motion capture systems (IMSs). This relatively new technology uses accelerometers, gyroscopes and magnetometers, contained in small integrated measurement units fixed to the subject's body, to track 3D human motion. Unlike current "golden standard" optical systems, IMSs are portable, less expensive and easier to use. This allows for the capture of human kinematics in the natural environment instead of in a laboratory and introduces numerous novel possibilities for field-testing. This study evaluated the use of an IMS for outdoor sports performance analysis, using road cycling as a case study. The objectives were to examine the level of interference in the magnetic sensor data related to materials in high-performance road bicycles and to investigate trends in knee flexion amongst top road cyclists. Ten male cyclists completed one indoor laboratory test on a stationary trainer and one outdoor road test on their own bicycle. Each test contained three one-minute recordings, at constant power levels of 2, 3.5 and 5.5 W.kg~(-1). While laboratory measurements indicated significant disturbances, results showed that the outdoor magnetic field was homogenous. Moreover, although most sensors were undisturbed there were unacceptable magnetic field distortions at the pedal-shoe and hand-handlebar interfaces. Therefore, accurate measurements of full-body cycling kinematics are not currently possible with most competition-level road bicycles. However, knee flexion measurements are possible without the magnetometer data. Results showed significant variations in maximum (118.1+-7.0 deg), minimum (33.1+-7.7 deg) and range (84.66 +- 6.32 deg) of knee flexion of up to 33.9 deg, 31.0 deg and 28.7 deg respectively. This supports the use of dynamic bicycle fit methods to determine optimal saddle height and saddle fore-aft position. Future work could include the design of a customized road bicycle free of ferromagnetic materials to make more detailed studies of outdoor road cycling kinematics possible.