The Effectiveness of A Training Program Using  Vertical Jump Device (Vertimax) on Some Biomechanical Variables in  Performance of  Undulating Serve Skill in Volleyball for Players. JPKO [Internet]. 2026 Apr. 9 [cited 2026 Aug. 22];2(2):27-44. Available from: https://journalpejuang.web.id/index.php/jurnalpkopejuang/article/view/91