Kusuma, Hangga, and Anies Setiowati. “PENGARUH WILLIAM FLEXION EXERCISE TERHADAP PENINGKATAN LINGKUP GERAK SENDI PENDERITA LOW BACK PAIN”. Journal of Sport Science and Fitness 4, no. 3 (1). Accessed May 11, 2024. https://journal.unnes.ac.id/sju/jssf/article/view/7370.