Prevalensi nyeri punggung bawah sederhana dan faktor yang berpengaruh pada pekerja angkat angkut manual (penilaian faktor risiko berdasarkan The Revzlved National Institute for Occupational Safety and Health 1994) = The Prevalence of simple low back pain and affected factors among manual handling workers (lifting index based on The Revised National Institute for Occupational Safety and Health 1994)