Can a more neutral position of the forearm when operating a computer mouse reduce the pain level for VDU operators?

Abstract

A prospective epidemiological field study covering a 1-year period has been published (Int. J. Hum.–Comput. Interaction, 1999; 2001). The aim of the study was to investigate if subjects with existing musculoskeletal pain experience a reduction in pain development when using a new mouse design (Anir/Renaissance) which allows a more neutral position of the wrist, compared with a traditional mouse. The study population consisted of 67 participants with average intensity of pain during the last 6 months of approximately 50 mm on a 100 mm visual analog scale (VAS). The total group was randomly divided into one intervention group and one control group. The study was performed as a prospective parallel group design. VAS was used to assess the average level of pain in the musculoskeletal system during the last 6 months. This was a three-part study; the first two parts of which have already been reported. In part I, it was found that after using Anir mouse for 6 months, there were significant reductions in pain for neck, shoulder, forearm, wrist and hand (Int. J. Hum.–Comput. Interaction 11(2) (1999) 79). The control group, using the traditional mouse reported no significant changes in the pain level. In part II, The Anir mouse was given to the control group 6 months after the start of the study. After 6 months of using the Anir mouse, the former control group reported a significant reduction in pain for neck, shoulder, forearm, wrist and hand. The group getting the initial intervention reported still significant reductions of pain in the upper part of the body, 12 months after the start of the study (Int. J. Hum.–Comput. Interaction 13(1) (2001) 13). The present paper covers the period from 1 to 3 years of the study. By inspection of the mean values of pain over time, no relevant changes seem to have appeared in the period from 12 to 36 months. No significant changes in confounding factors were found during the period from 12 to 36 months. The results from this study indicate the importance of using a more neutral position of the forearm when using a computer mouse.

Relevance to industry

This paper presents indications that a more neutral position of the forearm when operating a computer mouse is an important source of pain reduction in the upper part of the body. Several researchers have reported a relationship between the overall duration of mouse use and pain development. Further, the time using a computer mouse is steadily increasing due to the widespread application of graphical user interfaces.

Introduction

The number of workers and the duration of use of visual display units (VDU) are increasing. In Sweden, 45% of males and 55% of females of the total VDU workforce, used VDU more than 50% of the work time (Arbetarskyddsstyrelsen, Statistiska centralbyrån, 1999). The use of graphical user interfaces has increased the use of computer pointing devices such as mice. Wiagaeus Tornqvist et al. (2000) found in a study of 1555 VDU operators that 96% used a traditional computer mouse. Further, musculoskeletal discomfort is reported to increase due to mouse usage (Fogleman and Brogmus, 1995). A relationship between overall duration of mouse use and pain in the upper extremity is reported (Karlqvist et al., 1996; Aarås et al., 1998). Mouse use is documented to create static load in the forearm extensor with very few gaps in the EMG level (Jensen and Laursen, 2000). The presence of lower number of gaps during work has been shown to be a risk factor for development of musculoskeletal symptoms in the trapezius muscle (Veiersted et al., 1993). Supporting the forearm is important in reducing the muscle load on the extensors of the forearm when operating a mouse compared to no support or only wrist support (Aarås et al., 1997; Wahlstrøm et al., 2000).

The underlying mechanism that causes discomfort and pain in the musculoskeletal system is not well known. According to Hägg (1991), long lasting activity of single muscle fibers may overload their capacity and start a damaging process, with pain as an end result. This is supported by Thorn et al. (2001). They found single motor units to be active 20–30 min or more. Läubli et al. (1999) hypothesize that interactions between individual muscle activation patterns and certain repetitive tasks may cause overloading of the involved muscles.

The background for this study was based on the following findings in a laboratory study. The workload of the extensors of the forearm was significantly less when using a mouse (Anir, now called Renaissance) giving a more neutral position of the forearm (Fig. 1) compared with a traditional mouse requiring a more pronated forearm. This was true for the extensor digitorum communis. The same clear tendency was also found regarding extensor carpi ulnaris (Aarås and Ro, 1997).