title: System and modelling errors in motion analysis: implications for the measurement of the elbow angle in cricket bowling.
abstract: The system and modelling errors of two fundamentally different motion capture systems (opto-reflective vs. video-based) were tested under various conditions, to determine their ability to accurately measure flexion-extension of the elbow angle in cricket bowling. A mechanical arm was used for all testing, that enabled known elbow flexion-extension and abduction ("carry") angles to be manually set. The root mean squared (RMS) error of 0.6 degrees for the opto-reflective system (Vicon-612) was more accurate in reconstructing a known angle than the video-based system (Peak Motus) (RMS error 2.3 degrees ) in the laboratory, when the same mathematical procedure (model) was applied to calculate the elbow flexion-extension angle. When different models were applied to the raw marker trajectories collected using the video-based system, RMS was lowest for the external marker segmental cluster models (2.3 degrees ) compared with 9.4 degrees for the vector and 4.5 degrees for the projected vector approaches, where joint centres were visually approximated. Real world, field-based comparisons using the video-based system showed that occluding the arm and therefore the shoulder, elbow and wrist joint centre locations by placing a shirt on the arm, increased RMS error for both vector (7.8 degrees -9.0 degrees ) and projected vector (4.3 degrees -5.1 degrees ) modelling approaches.
authors.affiliation: School of Human Movement and Exercise Science, The University of Western Australia, 35 Stirling Highway, Crawley, Perth 6009, Australia. Bruce.Elliott@uwa.edu.au
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Elliott
authors.forename: Jacqueline A
authors.initials: JA
authors.lastname: Alderson
authors.forename: Eliot R
authors.initials: ER
authors.lastname: Denver
mesh_terms: D001132:Arm / Q000502:physiology*; D004550:Elbow / Q000502:physiology*; D004551:Elbow Joint / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D009068:Movement / Q000502:physiology*; D015203:Reproducibility of Results; D013177:Sports; D014953:Wrist / Q000502:physiology; D014955:Wrist Joint / Q000502:physiology