Ergonomics Intervention

Abstract

This study described a simple ergonomic intervention and evaluation of its implementation in bolting task assembly. Ergonomics tools will be utilised to give a better understanding of the success of the intervention in lowering musculoskeletal disorders especially towards the upper limb region. In the study, two different height of bolt assembly horizontal bar were utilised in a bolting task for a set of subjects. Result has shown that height (environment) factor in bolting task may play a role in development of early symptoms of upper limb disorders.

1.0 Introduction

Injuries to the musculoskeletal system are common in workplace. However, many injuries such as muscle and ligament strains are not the result of a sudden mishap, but occur over time as a result of repeated microtraumas. Such type of injury does not develops immediate but through time. There are three main risk factors that contribute to cumulative trauma disorders (CTDs): force, repetition, and awkward postures. Any one or combination of the factors contributes to development of CTDs or musculoskeletal disorders(MSD).

Lower back pain and wrist pain had always been given due attention in MSD literatures. Nonetheless, in recent years, occupational-associated pain and disorder of shoulder had been moving up the prevalence chart too. Results from the latest survey of self-reported work-related illness Labour Force Survey indicate that in 2005/06 an estimated prevalence of 374 000 people in Great Britain suffered, in their opinion, from a musculoskeletal disorder mainly affecting the upper limbs or neck that was caused or made worse by their current or past work. This equates to 870 per 100 000 people (0.87%) who have ever worked in Great Britain. In addition, according to US Bureau of Labor Statistic, shoulder injuries/illnesses needs the longest day (15 days) away from work for recovery as compared to wrist (14 days) back and neck 7days respectively. Hence, a paradigm shift has to take place to view CTD in a broader spectrum and not restricted to certain part of body(i.e. low back).

Gradual increase of general upper limbs disorder in global health and safety statistics annually should be a great motivation for ergonomists to have greater input into protecting active workforce especially in aging developed countries. Simple effective intervention has to take place even with simple task to curb CTDs in our workforce. Hence, this study will look into simple ergonomic intervention for manual bolting task which occurs frequently across global workforce in different industries. The study will look into simple cost effective intervention to reduced physical work load and improved performance if possible.

Putz Anderson(1988) postulates a 'risk model' for CTDs, based on the interaction of four main factors: repetitiveness, force; posture and lack of recovery. In this study, the main intervention of the task set up will be towards the horizontal bar height. The aim of such intervention is to provide a better posture for 'workers' and substantially reduce the risk exposure towards upper limbs region. By providing better postural position for 'workers', a significant improvement on task efficiency should be expected.

2.0 Materials and Methods

2.1 Simulated Task

Four subjects (2 male and 2 female) participated in this test. The mean age was 37.5 (SD = 6.56, Range = 29-45). Their mean stature are 178cm (SD = 9.31cm, Range =165 - 187 cm).

The simulated task is to assemble bolts onto a horizontal bar which was set at the height corresponding to 50% of British adult standard (1740 mm) and 50% of British adult elbow heights (1100 mm). In completing the task, subjects had to picked up a bolt from a box (positioned on a table on the left hand side) and inserted the bolt into a horizontal hole with the end of the bolt facing downwards. Subsequently, subjects were to assemble a nut onto the bolt and tightened it with a spanner.

Subjects repeated the same task continuously for 28 bolts. In addition, they were asked to assume that they were paid for the number of bolts assembled and the task was to be performed up to 2-4 hours per day. The task was divided into two sessions with either "higher bar" or "lower bar" assembly for each session. Such sessions are randomised among subjects and each subject is given at least 15 minutes rest between the two sessions.

2.2 Data analysis

2.2.1 Subjective ratings of fatigue

The subjects were asked to rate the intensity of fatigue of upper limbs region on a RPE Scale (Borg, 1988) at the end of each bolting task sessions. A larger score in the Borg REP Scale indicates a higher perceived intensity of task by each subject.

2.2.2 Subjective ratings of postural discomfort

Subjects were asked to rate any postural discomfort after each task session (Corlet, 1976). A larger score in the Discomfort Scale for a subject indicates a perceived higher discomfort towards specific upper limb cause by completion of task.

2.2.3 Physical Exposure Level

Subjects were risk assessed with a Quick Exposure Check (QEC) Level Tool (Buckle & Li, 1996). By utilising QEC tool, subjects will be risk assessed for the exposure level in the task for before and after ergonomics intervention. Result of a lower exposure level by QEC tool after ergonomics intervention will prove a positive improvement of bolting task.

2.2.4 Total Task Cycle Time

Each subject was timed for the completion of bolting task for each horizontal bar height. If lower time cycle was achieved for elbow height horizontal bar (Lower bar height) hence it will show a positive result upon ergonomics intervention. If result of significant p < 0.05, t test hence bar height will be a significant improvement factor in bolting task.

3.0 Result

Figure 1 : Bolting task cycle time for upper and lower horizontal bar height

Figure 1 shows that the total time for subject to complete each of its bolting task on different horizontal bar height. The mean time for completion of bolting task with horizontal bar at 50% British adult stature height is 475.75 seconds (SD = 125.56 s , range= 309 -613 s). While the mean cycle time for lower horizontal bar at 50% British adult elbow height is 425.25s (SD=78.12,