Application of the Cube Model for Biomechanical Exposure Assessment of Combined Manual Material Handling Tasks in a Manufacturing Plant in India

OCCUPATIONAL APPLICATIONS In this study, a biomechanical exposure assessment methodology for combined manual material handling tasks is devised using the “cube” model approach (including time, force, and posture), specifically by modifying the model dimensions. The resulting modified cube model aims to facilitate biomechanical exposure assessment of manual material handling tasks, particularly for industrial conditions where a chain of combined manual material handling activities is carried out across a wide geographical area, and where no direct measurements of biomechanical exposures are available. This methodology can help in prioritizing high-exertion manual material handling tasks for subsequent ergonomic analysis and redesign. TECHNICAL ABSTRACT Background: Biomechanical exposure measurement is difficult for combined manual material handling tasks in field settings and/or resource-constrained environments. “Cube” models—integrating time, force, and posture—have been used previously, but existing models have not been applied to manual material handling tasks. Purpose: The objective of this study was to develop a revised cube model as a biomechanical exposure assessment tool for combined manual material handling tasks. Methods: The study was conducted in a bearing manufacturing plant in India. First, a work-sampling approach was used to observe all manual material handling tasks and record relevant details. Then, two modified models—cube model 1 and cube model 2—were developed by modifying the existing cube model dimensions; physical load intensity and overall physical load were calculated using these two models under a novel cumulative exposure measurement framework. Decision criteria for cumulative cube score were formulated to classify manual material handling tasks under three physical load levels (i.e., low, medium, and high). Finally, cube model assessments were compared with biomechanical assessments of all manual material handling tasks. Results: Attribute agreement (overall correct classification) values for the existing cube model, cube model 1, and cube model 2 were 39%, 61%, and 69%, respectively, indicating better performance for cube model 2. Spearman rank order correlations comparing cumulative cube scores with cumulative biomechanical measures ranged from 0.73 to 0.94, which is considered to be high. Conclusions: The study presents a methodology to assess biomechanical exposures for combined manual material handling tasks by modifying the existing cube model. A cumulative dose concept as applied in biomechanical analysis was used in the study. The cumulative cube score is proposed as a proxy to indicate the overall biomechanical exposure during a combined manual material handling task. Cumulative cube scores gave good agreement between cube model 2 evaluations and biomechanical evaluations, supporting its applicability for evaluating manual material handling tasks.