Assessing effects of environmental factors on physical workload during motor-manual timber harvesting using motion capturing data and biomechanical modeling

Forestry workers are at significant risk to suffer from work-related musculoskeletal disorders (WMSD). Challenging environmental factors of the forest can have a significant impact on physical workload of motor-manual timber harvesting, which is already considered highly physical work. Conventional observation methods of risk assessment may underestimate specific environmental factors that influence forestry work. In order to determine whether such factors can increase the risk of WMSD and should therefore be integrated into standard risk assessment methods, a field study was conducted with N=10 forestry workers. The effects of environmental factors on physical workload were analyzed using motion capturing, force measures and biomechanical parameters for the activity of manually pulling a steel cable from a skidder winch over a distance of 20 meters in the forest. Type of execution, ground condition and soil slope as environmental factors were varied to investigate their effects on biomechanical parameters. Compressive force and shear force on the L5/S1 disc were calculated using a biomechanical approach. The results indicated that mean compressive and mean shear forces differed significantly depending on the environmental factors type of execution and soil slope. No significant influence of the factor ground condition was found. The combination of all environmental factors showed a significant interaction effect on mean compressive and shear forces. The average maximum values of compressive force did not exceed recommended load limits. However, the average maximum values of shear force exceeded recommended load limits repeatedly by more than 30%, which clearly indicates a health risk. The findings of this biomechanical approach were compared to an assessment with the Key Indicator Method for pushing and pulling, which is a conventional observational method for risk assessment. The comparison indicated that this conventional method might systematically underestimate the influence of some environmental factors in the forest and thus may also underestimate a potential health risk.