Hamdani, Muhammad Zeeshan Haider, et al. “NORMATIVE REFERENCE STANDARD FOR CORE MUSCULAR ENDURANCE OF ADOLESCENT 12-16 YEARS FROM SOUTH PUNJAB PAKISTAN: A CROSS-SECTIONAL STUDY”. Pakistan Journal of Physiology, vol. 18, no. 1, Mar. 2022, pp. 3-8, https://pjp.pps.org.pk/index.php/PJP/article/view/1440.