Muhibbi, M., T. Hidayah, and S. Sulaiman. “The Develoment of Speed Punch Reaction (SPR) As a Tool for Reaction Speed of Karate Punch Training”. Journal of Physical Education and Sports, Vol. 7, no. 2, July 2018, pp. 168-73, https://journal.unnes.ac.id/sju/jpes/article/view/25124.