Objective: To determine whether a composite metric of arm elevation and trapezius activity (i.e. neck/shoulder load) is more strongly associated with the 2-year course of neck and shoulder pain intensity (NSPi) among construction and healthcare workers than each exposure separately.

Methods: Dominant arm elevation and upper trapezius muscle activity were estimated in construction and healthcare employees (n=118) at baseline, using accelerometry and normalized surface electromyography (%MVE), respectively. At baseline and every six months for two years, workers reported NSPi (score 0-3). Compositions of working time were determined for arm elevation (<30°; 30-60°; >60°), trapezius activity (<0.5 %; 0.5-7.0 %; >7.0 %MVE), and a composite metric “neck/shoulder load” (restitution, low, medium, and high load). Associations between each of these three compositions and the 2-year course of NSPi were determined using linear mixed models.

Results: Associations between exposure compositions and the course of NSPi were all weak and in general uncertain. Time spent in 0.5-7.0 %MVE showed the largest and most certain association with changes in NSPi during follow-up (β=-0.13; p=0.037; corresponding to a -0.01 change in NPSi every 6 months). Among pain-free workers at baseline, medium (β=-0.23; p=0.039) and high (β=0.15; p=0.031) neck/shoulder load contributed the most to explaining changes in NSPi.

Conclusions: The composite metric of neck/shoulder load did not show a stronger association with the course of NSPi than arm elevation or trapezius activity alone in the entire population, while some indications of a stronger association were found among those who were pain-free at baseline.