Are Planar Simulation Models Affected by the Assumption of Coincident Joint Centres at the Hip and Shoulder?

Planar simulation models which assume coincident joint centres at the hip and shoulder are often used to investigate subject-specific maximal performances rather than 3D models due to the viability of determining subject-specific parameters. To investigate the effect of coincident joint centres on model accuracy, three variants of a 16-segment planar subject-specific angle-driven model were evaluated using an elite cricket fast bowling performance: (a) planar representation assuming coincident joint centres; (b) planar representation with non-coincident hip joint centres; (c) planar representation with non-coincident hip and shoulder joint centres. Model (c) with non-coincident hip and shoulder joint centres best matched the recorded performance with better estimates of the ground reaction force (mean RMS differences: (a) 18%; (b) 12%, (c) 11%) and ball release velocity (mean RMS differences: (a) 3.8%, (b) 3.2%, (c) 1.7%) due to a better representation of the mass centre location and link system endpoint velocity. Investigations into the subject-specific performance of maximal effort movements, where non-sagittal plane rotations of the pelvis and torso could affect model accuracy, should consider the use of non-coincident hip and shoulder joint centres within a planar model rather than using a simple planar model or a full 3D model.