The dynamics of performance in professional sport requires a systematic improvement of the training process. Such activities should also include optimizing the children and youth training in these disciplines, where an early specialization operates. The main aim of this paper was to search for the relationship between swimmer’s segmental kinematics (segmental velocities, stroke rate, stroke length, stroke index); the relationship between swimmer’s technical skill level (in four competitive swimming techniques) and training overloads taking into consideration gender and age effect. The study group consisted of 121 swimmers (69 female and 52 male), of the Polish 12–15 age group swim team, volunteered to serve as subjects. Video-based methods and video equipment are being applied to assist qualitative and simple quantitative analysis for immediate feedback and research in swimming. Both technical skill level preparation and segmental kinematics of 12–15 year old swimmers proved to be highly conditioned by implemented training intensity ( p < 0.001), as well as the volume of training (high and average trade at a level of significance p < 0.001). Implemented training overloads expressed by both volume and intensity of training showed high and very high correlation with the swimming efficiency, presented segmental kinematics and technical skill level, however, there appeared particularly pronounced relationship with the size of kinematic parameters taken into account in four competitive swimming techniques, components of the 100 m individual medley.