Effects of work surface and task difficulty on neck-shoulder posture and trapezius activity during a simulated mouse task.

OBJECTIVES: The purpose of this study is to evaluate the influence of the work surface and task difficulty on the head, upper back and upper arm postures and activity of the descending trapezius during a simulated mouse task.

METHODS: Healthy female university students (N = 15) were evaluated. The work surface was positioned at elbow height (EH) and above elbow height (AEH) and the task difficulty was set at low (LD) and high (HD) levels. The postures were recorded by inclinometers. Trapezius activity was normalized by the maximum voluntary isometric contraction (MVIC).

RESULTS: Significantly higher head flexion was found at EH compared to the AEH condition, with an average difference of 2°-5° at the same difficulty level. The HD task significantly increased head (3°-6°) and upper back flexion (6°-7°) at the same table height. For upper arm elevation and trapezius activation, the AEH condition presented higher upper arm elevation (about 6°-8°) and trapezius activity (0.8-1.4% of MVIC), regardless of the difficulty level of the task.

CONCLUSIONS: Head posture was influenced by the table height and task difficulty; the upper back posture by high difficulty; and upper arm posture and trapezius activity were only influenced by table height.