“ 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”. Jurnal Pendidikan Kepelatihan Olahraga: PEJUANG, vol. 2, no. 2, Apr. 2026, pp. 27-44, https://journalpejuang.web.id/index.php/jurnalpkopejuang/article/view/91.