markerless analysis of front crawl swimming

research on motion analysis of swimmers is commonly based on video recordings of the subject's motion, which are analyzed by manual digitization of feature points by an operator. this procedure has two main drawbacks: it is time-consuming, and it is affected by low repeatability. therefore, the application of video-based, automatic approaches to motion analysis was investigated. a video-based, markerless system for the analysis of arm movements during front crawl swimming was developed. the method proposed by corazza et al. (2010) was modified in order to be used into water environment. three dimensional coordinates of shoulder, elbow and wrist joints centers of 5 sprint swimmers performing front crawl swimming were determined. wrist joint velocity was also calculated. accuracy and reliability of the proposed technique were evaluated by means of comparison with traditional manual digitization (simi reality motion systems gmbh). root mean square distance (rmsd) values between trajectories estimated with the two techniques were determined. results show good accuracy for wrist joint (rmsd<56 mm), and reliability, evaluated on one subject, comparable to the inter-operator variability associated with the manual digitization procedure. the proposed technique is therefore very promising for quantitative, wide-scale studies on swimmers' motion.