THE EFFECT OF WILLIAM’S FLEXION EXERCISE ON THE LEVEL OF BACK PAIN DOWNTOWN ELDERLY IN THE TRESNA SOCIAL INTEGRATED SERVICE UNIT WERDHA BLITAR IN TULUNGAGUNG DISTRICT. unita [Internet]. 2022 Nov. 1 [cited 2025 Sep. 29];4:23-3. Available from: https://conference.unita.ac.id/index.php/conference/article/view/73