arunmek, wisanu. “EFFECT OF CORE MUSCLES TRAINING ON STRENGTH AND SPEED OF 50 METERS CRAWL STROKE”. Academic Journal of Thailand National Sports University, vol. 14, no. 2, Apr. 2022, pp. 253-64, https://he02.tci-thaijo.org/index.php/TNSUJournal/article/view/248633.