Exploring the use of the RCRA equation as an MSD risk assessment tool to evaluate electrical harness installation tasks.

Abstract

Intro: Electrical wire harnessing on an automotive line consists of routing a harness through a car’s engine, securing electrical connections, and successfully securing retention clips to keep the harness in place. The wire harnessing task is complex in nature and installation involves many hand forces and repetitive motions. Additionally, wire harnessing is highly repetitive, with workers having to install up to 500 engine harnesses per shift. Anecdotal evidence is emerging that some wiring harnessing work can lead to workplace musculoskeletal disorders of the hand and wrist. Due to the complex nature of the task, and difficultly in measuring internal exposures in-field by using tools such as electromyography, there is a lack of quantification and analysis of biomechanical demands of the task. The Recommended Cumulative Rest Allowance (RCRA) tool, developed by Potvin & Gibson (2016), aims to characterize exposures by assessing isolated subtasks in conjunction with other subtasks to assess the risk of a complete job. The RCRA is informed by percent efforts (%Efforts) that can vary and result in different outcomes based on inputs. Thus, there is a need to quantify and analyze biomechanical demands of wire harnessing using both high-fidelity in-laboratory equipment and potential lower-fidelity in- field equipment to compare and validate a cumulative tool to be used on the line. This study aimed to evaluate the usability of the RCRA tool for estimating required rest necessary to prevent undue fatigue during harness installation. Methods: Using a mock-engine setup in a controlled laboratory environment, 26 participants completed repeated installations of two harness types while surface electromyography (EMG) and force data were collected for wrist flexors, extensors, and applied hand force. RCRA ratios were calculated across subtasks and input types including muscle activity as a percent of maximum voluntary contraction of the wrist flexors and extensors and applied force as a percent maximum voluntary force to assess fatigue accumulation. Results: Findings revealed that input selection significantly influenced RCRA outputs, with applied force and wrist flexor EMG producing consistent and interpretable estimates of required rest allowances. In contrast, peak wrist extensor inputs often resulted in unrealistically high RCRA ratios due to the extensor muscle’s sustained activation patterns and the equation’s sensitivity to frequency and duration. No significant differences were found between the two harness types, likely due to their similar physical characteristics. Conclusion: Overall, this study supports that the RCRA tool yields similar outputs when driven with peak force or peak wrist flexor EMG, but not when driven with peak extensor EMG. It also underlines the need for careful input selection and complementary assessment strategies when evaluating different muscles. These insights provide a foundation for developing validated, in-field fatigue assessment protocols to help prevent overuse injuries in automotive manufacturing.