Pornchalitkittiporn, S., and T. Gulthawatvichai. “JOB PERFORMANCE ACHIEVEMENT MOTIVATION OF PERSONAL TRAINER AT FITNESS CENTER IN BANGKOK”. Journal of Sports Science and Health, vol. 22, no. 3, Dec. 2021, pp. 370-83, https://he02.tci-thaijo.org/index.php/spsc_journal/article/view/255650.