Indah Zunita (2025) “The relationship between self-confidence and concentration with the ability to smash volleyball athletes 12-17 years old in pervas club ”, Jorpres (Jurnal Olahraga Prestasi), 21(2), pp. 57–66. Available at: https://jurnal.uny.ac.id/index.php/jorpres/article/view/95718 (Accessed: 23 May 2026).