This randomized single-blind crossover trial investigated the acute effects of three different exercise modalities, namely self-myofascial release with a foam roller, dynamic stretching, and static stretching, on posture, flexibility, dynamic balance, and lower-extremity performance in adolescent karate athletes (12-18 years). Participants attended four weekly sessions at the same time of day and after a 48-hour rest period. In the first week a baseline (control) measurement was performed, and in the following three weeks each participant received the three interventions in a randomized order. Outcomes included a four-view smartphone-based posture analysis (PostureScreen Mobile), the Sit-and-Reach Test, the Y Balance Test, the 30-second Sit-to-Stand Test, and the Vertical Jump Test (My Jump Lab 2). The aim was to identify which warm-up modality offers the greatest acute benefit before karate-specific performance