THE HEAVY LOAD OF THE BACKPACK ON THE SHOULDER POSITION AT THE AGE OF 12-15 YEARS AT SMPN 56 SURABAYA. BIOMA [Internet]. 2024 Apr. 20 [cited 2025 Apr. 30];13(1):29-35. Available from: https://journal2.upgris.ac.id/index.php/bioma/article/view/375