Aim

To investigate if trapezius muscle activity increases over time during visually demanding near work.

Methods

The vision task consisted of sustained focusing on a contrast-varying black and white Gabor grating. Sixty-six participants with a median age of 38 (range 19–47) fixated the grating from a distance of 65 cm (1.5 D) during four counterbalanced 7-min periods: binocularly through −3.5 D lenses, and monocularly through −3.5 D, 0 D and +3.5 D. Accommodation, heart rate variability and trapezius muscle activity were recorded in parallel.

Results

General estimating equation analyses showed that trapezius muscle activity increased significantly over time in all four lens conditions. A concurrent effect of accommodation response on trapezius muscle activity was observed with the minus lenses irrespective of whether incongruence between accommodation and convergence was present or not.

Conclusions

Trapezius muscle activity increased significantly over time during the near work task. The increase in muscle activity over time may be caused by an increased need of mental effort and visual attention to maintain performance during the visual tasks to counteract mental fatigue.

Poor visual ergonomics is associated with visual and neck/shoulder discomfort, but the relation between visual demands and neck/shoulder muscle activity is unclear. The aims of this study were to investigate whether trapezius muscle activity was affected by: (i) eye-lens accommodation; (ii) incongruence between accommodation and convergence; and (iii) presence of neck/shoulder discomfort. Sixty-six participants (33 controls and 33 with neck pain) performed visually demanding near work under four different trial-lens conditions. Results showed that eye-lens accommodation per se did not affect trapezius muscle activity significantly. However, when incongruence between accommodation and convergence was present, a significant positive relationship between eye-lens accommodation and trapezius muscle activity was found. There were no significant group-differences. It was concluded that incongruence between accommodation and convergence is an important factor in the relation between visually demanding near work and trapezius muscle activity. The relatively low demands on accommodation and convergence in the present study imply that visually demanding near work may contribute to increased muscle activity, and over time to the development of near work related neck/shoulder discomfort.

Visually demanding near work can cause eye discomfort, and eye and neck/shoulder discomfort during, e.g., computer work are associated. Here, to investigate direct effects of experimental near work on eye and neck/shoulder discomfort, 33 individuals with chronic neck pain and 33 healthy control subjects performed four visual tasks, rating eye and neck/shoulder discomfort at baseline and after each task. The cumulative performance time (reflected in the temporal order of the tasks), astigmatism, concurrent eye discomfort, and extent of accommodation all aggravated neck/shoulder discomfort. There was an interaction effect between the temporal order and eye discomfort: participants with a greater mean increase in eye discomfort also developed more neck/shoulder discomfort with time. Since moderate musculoskeletal symptoms are a risk factor for more severe symptoms, it is important to ensure a good visual environment in occupations involving visually demanding near work.

Near work is associated with increased activity in the neck and shoulder muscles, but the underlying mechanism is still unknown. This study was designed to determine whether a dynamic change in focus, alternating between a nearby and a more distant visual target, produces a direct parallel change in trapezius muscle activity. Fourteen healthy controls and 12 patients with a history of visual and neck/shoulder symptoms performed a Near-Far visual task under three different viewing conditions; one neutral condition with no trial lenses, one condition with negative trial lenses to create increased accommodation, and one condition with positive trial lenses to create decreased accommodation. Eye lens accommodation and trapezius muscle activity were continuously recorded. The trapezius muscle activity was significantly higher during Near than during Far focusing periods for both groups within the neutral viewing condition, and there was a significant co-variation in time between accommodation and trapezius muscle activity within the neutral and positive viewing conditions for the control group. In conclusion, these results reveal a connection between Near focusing and increased muscle activity during dynamic changes in focus between a nearby and a far target. A direct link, from the accommodation/vergence system to the trapezius muscles cannot be ruled out, but the connection may also be explained by an increased need for eye-neck (head) stabilization when focusing on a nearby target as compared to a more distant target.