Objectives: This study examined the changes in neck and back pain visual analog scale (VAS) scores, cervical range of motion (CROM), cervical flexion-relaxation ratio (FRR) and lumbar FRR after below-knee assembly work. Methods: Fifteen young male workers were recruited. Neck and back pain VAS scores, active CROM and cervical and lumbar FRRs were measured in all subjects once before and once after 10 minutes of below-knee assembly work. Results: The VAS scores for both neck and back pain increased significantly with below-knee assembly work. The CROM for all measures decreased significantly with below-knee assembly work. Both the cervical and lumbar FRRs on the left and right sides decreased significantly with below-knee assembly work. Conclusions: We postulate that 10 minutes of below-knee assembly work can increase neck and back pain and cause changes in the active CROM and cervical and lumbar FRRs.(J Occup Health 2014; 56: 150-156)