Assessment of occupational risk factors in the manual loading workplace using biomechanical assessment methods (REBA and PLIBEL) in a poplar plantation

Introduction: Manual loading of logs in poplar plantations chronically exposes workers to hazardous biomechanical factors such as awkward postures, heavy load lifting and carrying, and repetitive motions. A substantial body of evidence confirms the strong association between these factors and the development of work-related musculoskeletal disorders (WMSDs). However, a systematic ergonomic assessment of these occupational risk factors in this specific forestry sub-sector remains under-addressed. The primary objective of this study was to comprehensively analyze the work environment and working postures during manual loading operations using complementary ergonomic risk assessment tools, aiming to identify, prevent, and control biomechanical stresses imposed on workers, thereby reducing occupational injury rates and improving workforce health, safety, and productivity.
Method: This cross-sectional study was conducted in two compartments of the Tanian poplar plantation in Soumeh Sara, Guilan Province, Iran. The study population consisted of 40 male workers engaged in manual loading operations, with a mean age of 45 years, a mean height of 170 cm, and a mean work experience of 19 years. Workers manually handled logs with an average weight of 49.68 kg across three core tasks: lifting, carrying, and truck loading. Three complementary methods were employed: 1) The Body Map questionnaire was used to determine the 12-month prevalence and bodily distribution of musculoskeletal discomfort across nine body regions. 2) The PLIBEL ergonomic workplace assessment checklist identified primary ergonomic risk factors, including awkward postures, repetitive movements, and deficient workstation and tool design, linked to specific body areas. 3) The Rapid Entire Body Assessment (REBA) method was applied to biomechanically analyze postures during each of the three tasks. In REBA, scores for Group A segments (trunk, neck, legs) and Group B segments (upper arm, forearm, wrist) were computed for each task, followed by the integration of force/load scores (exceeding 10 N in all tasks), coupling quality, and activity type to determine the final REBA score and corresponding risk level. Joint angles were measured using a digital goniometer and video analysis. Statistical analyses were performed using Kolmogorov-Smirnov, Levene, and Kruskal-Wallis tests in SPSS version 23.
Results: Body Map data revealed that 43.33% of workers reported musculoskeletal symptoms in at least one body region. The highest prevalence was in the lower back (72.5%), spine (70%), and equally in the wrist, arm, and knee regions (47.5% each), whereas the thigh showed the lowest prevalence (12.5%). A significant difference in symptom prevalence across body regions was confirmed (P=0.02). The PLIBEL assessment identified the presence of “inappropriate workspace and tool design,” “forward bending and twisting of the trunk,” and “repetitive movements” as primary risk factors, predominantly affecting the neck, shoulder, trunk, wrist, forearm, and upper arm. Biomechanical analysis using REBA revealed a very high-risk profile for manual loading operations. The overall mean REBA score was 11.5, corresponding to a very high-risk level necessitating immediate corrective action (Action Level 4). Task-specific scores were 14 for lifting, 11 for carrying, and 9.5 for truck loading, classified as very high and high risk, respectively. The highest REBA scores per body part were assigned to the trunk during lifting, the neck and wrist during lifting and carrying, and the legs and upper arm during lifting.
Conclusion: The findings conclusively demonstrate that manual loading workers in this poplar plantation are exposed to an unacceptable level of biomechanical risk factors, making immediate ergonomic interventions imperative to prevent WMSDs. Corrective measures must be implemented across three domains: engineering controls (workstation redesign to eliminate floor-level loading and reduce load weight), administrative controls (job rotation, increased rest breaks, and systematic training in proper manual handling techniques), and personal protective equipment (e.g., knee pads). Ergonomically optimizing the loading process will not only safeguard worker health but also enhance productivity and contribute to sustainable development in forestry.