Firdaus, Kamal -. “THE EFFECT OF FARTLEX AND EXTENSIVE INTERVAL TRAINING METHOD TOWARD THE FOOTBALL REFEREES SPEED ENDURANCE IN PADANG”. JOURNAL OF SOCIAL SCIENCE RESEARCH 9, no. 1 (September 29, 2015): 1759–1764. Accessed May 14, 2024. https://rajpub.com/index.php/jssr/article/view/3773.