Musculoskeletal modelling for ergonomics: shoulder & low back loading in bricklaying

Abstract

In Great Britain, the number of Work-Related Musculoskeletal Disorder (WMSD) cases in 2015/16 accounted for 41% of cases of work-related illness. When compared to other industries, the building trade has one of the highest rates of WMSDs. There are many risk factors in construction that may contribute to the development of WMSDs: high hand forces, repetitive motions, and heavy, frequent, awkward lifting. Studies have shown that the development of WMSDs is driven by damage to the tendons, muscles or nerves due to high muscle and joint loading caused by these risk factors. Studies have also investigated the relationship between working height and mass lifted on muscle and joint loading and there are a several epidemiological studies on the effects of training. However, few musculoskeletal modelling studies have looked into work-related tasks; moreover, there has been no published work focused on bricklaying that has used dynamic musculoskeletal modelling to investigate muscle and joint loading. Thus, the aim of this thesis is to quantify the relationship between work-related activities and WMSDs in bricklaying tasks by determining the effects of training and experience, brick weight, and working height on upper limb kinematics, muscle forces, joint forces, and low back kinematics and net moments. It is hypothesised that by optimising bricklaying technique, a reduction in WMSDs through task design, equipment, and/or training can be achieved. Three different groups of participants were recruited. Seven experienced bricklayers, fifteen bricklaying trainees and seventeen healthy male participants with no experience of bricklaying (naïve) participated. Participants were asked to perform two bricklaying tasks. These were mortar spreading (Task I) and laying a brick (Task II). A simplified kinematic analysis of the low back was conducted and a musculoskeletal model was used to investigate joint and muscle forces at the shoulder. Results showed that kinematics of both the shoulder and low back present good repeatability, regardless of participants’ experience or training. For both tasks, working at 160 cm showed the highest glenohumeral (GH) abduction, with maximum mean values of 60º, 57º, and 59º for experienced, trainee and naïve participants respectively. Working at 160 cm also increased the maximum mean GH joint shear force, and middle deltoid, supraspinatus, and infraspinatus forces by at least 13.9%, 115%, 40%, and 82% for Task I and 74%, 34%, 73%, and 54% for Task II when compared to working at 0 cm. Reducing the working height from 160 cm to 0 cm resulted in an increase in low back net moment of up to 133% for Task I and 286% for Task II. The analysis of the influence of brick mass on the GH plane of elevation during Task II demonstrated differences in all groups of participants for all comparisons of 0.2 kg with 3.0 kg and 2.3 kg bricks (p=0.006); though similar differences were not found in GH adduction and GH internal rotation. Laying 3.0 kg bricks increased the GH compression and shear forces significantly from laying 0.2 kg bricks (p<0.01). All groups of participants showed higher forward flexion when laying 3.0 kg bricks compared to 0.2 kg bricks when working at 60cm and 0cm working heights (p=0.025); however, this study found no effect of brick mass on low back loading at all heights. This study demonstrated that laying 3.0 kg bricks resulted in significantly higher middle and posterior deltoid, supraspinatus and infraspinatus muscle forces than laying 0.2 kg bricks at all working heights. Results showed that the differences between the groups were focused more on kinematics than joint loading and muscles forces. In Task I, performed at the highest working height, higher GH internal rotation and plane of elevation were shown in naïve participants (p<0.001), while experienced participants showed higher GH abduction than naïve participants (p=0.02). The results also showed higher GH anterior shear forces in the groups of experienced participants and trainees when compared to naïve participants (p<0.05) for Task I; however, trainees demonstrated lower anterior shear forces when performing Task II compared to naïve participants (p=0.043). This suggested that experienced participants are at higher risk of developing muscle tears due to highly loaded joints and are more at risk of impingement due to high GH abduction in Task I. When bricklaying at ground level, significantly higher forward flexion was found in the last 50% of Task I in naïve participants compared to trainees and experienced bricklayers. These findings demonstrate that one desired effect of training is achieved – to avoid bending forward to reach lower working heights, a position well known to be a risk for back pain, bricklayers should squat. In Task II, experienced participants were found to have more forward flexion compared to both naïve participants and trainees for the first 80% of the motion, but significantly less forward flexion in the last 20% of the motion. Higher moments at the low back were found for working at ground level compared to the highest working height for all three groups for both tasks. This indicates that working height does have an effect on the risk of WMSDs. In conclusion, working at shoulder height might reduce back pain disorders; however, this is hypothesised to increase the risk of shoulder disorders. Working at mid-range found to be able to compensate for both risk.