Differences in the activation and co-activation ratios of the four subdivisions of trapezius between genders following a computer typing task

- Activation of UT, MT, and LT increased following 60 min of computer work.
- UT activation differed between genders following 60 min of computer work.
- Clavicular/upper trapezius ratio decreased following 60 min of computer work.

The aim of this study was to provide a description of gender differences of the activation patterns of the four subdivisions of the trapezius (clavicular, upper, middle, lower) following a 60 min computer work task. Surface EMG was collected from these subdivisions from 21 healthy subjects during bilateral arm elevation pre-/post- task. Subjects completed a standardized 60 min computer work task at a standard, ergonomic workstation. Normalized activation and activation ratios of each trapezius subdivision were compared between genders and condition with repeated measures ANOVAs. The interaction effect of Gender × Condition for upper trapezius% activation approached significance at p = 0.051with males demonstrating greater activation post-task. The main effect of Condition was statistically significant for% activation of middle and lower trapezius (p < 0.05), with both muscles demonstrating increase activation post-task. There was a statistically significant interaction effect of Gender × Condition for the Middle Trapezius/Upper Trapezius ratio and main effect of Condition for the Clavicular Trapezius/Upper Trapezius ratio, with a decreased ratio post-typing. Gender differences exist following 60 min of a low force computer typing task. Imbalances in muscle activation and activation ratios following computer work may affect total shoulder kinematics and should be further explored.