Baan, A. B., T. Rahayu, S. Soegiyanto, and S. Sulaiman. “Survey of Physical Fitness Level for Students With Mental Retardation on Extraordinary Elementary School in Donggala Regency”. Journal of Physical Education and Sports, Vol. 7, no. 3, Dec. 2018, pp. 236-41, https://journal.unnes.ac.id/sju/jpes/article/view/28156.