Changes in the cervical FRR, shoulder muscle pain and position after continuous detailed assembly work

Abstract

Several risk factors for upper-extremity muscle injuries are known, including repetitive and continuous-flow assembly work. However, no study has investigated the changes in the cervical flexion-relaxation ratio (FRR) and scapular position after continuous detailed assembly work. This study investigated the changes in the cervical FRR, trapezius muscle pain, and acromion and scapular positions after continuous detailed assembly work. Fifteen male workers were recruited. The cervical FRR, pressure-pain threshold (PPT) of the upper and middle trapezius muscle, and acromion and scapular positions were measured in all subjects once before and once after detailed assembly work. The cervical FRR after detailed assembly work was significantly decreased compared with that before detailed assembly work. The PPT of the upper and middle trapezius muscle after detailed assembly work was significantly decreased compared with that before detailed assembly work. The acromion angle after detailed assembly work was significantly decreased compared with that before detailed assembly work. The scapular inferior distance after detailed assembly was significantly increased compared with that before detailed assembly work. Our findings suggest that detailed assembly work may cause the absence of FRR, upper trapezius and middle trapezius pain, and scapular malalignment associated with a potential risk of neck and shoulder pain.