EFFECT OF A 7-WEEK CORE STABILIZATION PROGRAM ON BALANCE AND PERFORMANCE IN YOUNG RHYTHMIC GYMNASTS: A PILOT COMPARATIVE STUDY BETWEEN STABLE AND UNSTABLE SURFACES. - Veliki, Evangelia; Iakovidis, Paris; Kasimis, Konstantinos; Chatzilamprinos, Konstantinos; Chatziprodromidou, Ioanna P.; Apostolou, Thomas; Lytras, Dimitrios (Science of Gymnastics Journal, 2026)