Musculoskeletal Injuries, Sports Performance, Sports Specialization, and Quality of Life in Young Athletes

The primary aim of this observational cohort study is to assess sports specialization, sports performance, history of injuries (prevalence, types, areas, duration) and quality of life in young healthy athletes aged 8-16 from Poland. Athlete profiles will be created based on the variables (explained in detailed description) examined. Furthermore, the investigators will perform one-year injury follow-up. The main questions it aims to answer are: * Do athletes with a specific profile (lower values in athletic performance tests, low values in quality of life) evaluated at one time point, suffer injury in the future in annual observation? * Do athletes with high sports specialization will sustain injury in one-year follow-up? * Does sports specialization have a relationship with sports performance tests, and quality of life? * Does sport specialisation, training volume, geographical factor relate to injury history? * Does sports specialisation, injury history differ between sports (individual and team sports)? * Does value of the specific muscle (lower limb) isometric strength will be associated with the dynamic balance scores in young healthy athletes?