“ 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” (2026) Jurnal Pendidikan Kepelatihan Olahraga: PEJUANG, 2(2), pp. 27–44. Available at: https://journalpejuang.web.id/index.php/jurnalpkopejuang/article/view/91 (Accessed: 17 April 2026).