A multibody methodological approach to the biomechanics of swimmers including hydrodynamic forces

One of the main limitations in the musculoskeletal modeling and analysis of swimmers is the acquisition of external forces, which precludes the estimation of internal forces, crucial for advancing knowledge on swimming biomechanics. Computational simulations allow an estimation of these forces, and Swumsuit (SWimming hUman Model with Synthetic User Interface Tools), an open-source software, stands out for its computational efficiency and acceptable accuracy. However, differences in model discretization and formulation have conditioned its wider use in musculoskeletal analysis of swimming. The aim of this study is to propose a methodology for inverse dynamic analysis of swimming activities, based on a Cartesian-coordinate formulation, which integrates acquisition of motion-capture data, estimation of hydrodynamic forces by Swumsuit, and computation of the internal forces acting on the human body. To demonstrate the proposed methodology, an inverse dynamic analysis of a 3D full-body biomechanical model of the human body is performed for a six-beat front-crawl swimming stroke, acquired at the LABIOMEP-UP. The hydrodynamic forces, intersegmental forces, and joint torques computed are consistent with the literature for similar motions, which provides confidence in the proposed methodology. Although the proposed methodology is demonstrated for a front-crawl swimming stroke, it can be generalized to any swimming motion that Swumsuit can handle.