Low Back Stress in Commercial Crab Fishermen

Abstract

Commercial fishermen work long hours in an unpredictable and dynamic natural environment. The physical demands of the job include considerable strength, coordination, and endurance which expose the fishermen to many of the recognized risk factors for work-related musculoskeletal disorders. In particular, the manual materials handling activities on the unstable and dynamic work surface pose a particular risk for low back injury. The focus of this project was to quantify the biomechanical stresses placed on the lumbar spine during the work activities of commercial crab fishermen using the Continuous Assessment of Back Stress (CABS) method (Mirka et al, 2000) for the prioritization of the various work tasks for ergonomic intervention on a three-man crabbing crew. Continuous video footage was captured for a three-man crabbing crew that captured all of the work activities of each member of the crew throughout the workday. Using the CABS method, two aspects of the video data were captured in order to produce time-weighted histograms of back stress. First, each crewman's job was broken down into a series of subtasks. Analysis of the videotapes allowed for a temporal characterization of the amount of time spent in each of these subtasks. Second, three-dimensional stick figure models were constructed for each subtask and the biomechanical loads on the spine (compression, sagittal plane moment, coronal plane moment, transverse plane moment) were calculated using the University of Michigan Static Three-Dimensional Static Strength Prediction Program. These stick figure data were then used to arrive at the input variables of the NIOSH Revised Lifting Equation. Finally, each of these subtasks was performed in the laboratory using the Lumbar Motion Monitor to capture the necessary input variables to the OSU LMM model. Using the temporal information from the video analysis along with the output measures from each of the three risk assessment models, histograms of percent time at different levels of spinal stress assessments were generated. The results of this analysis, expressed in terms of time-weighted histograms, showed considerable variability in. spine loads both within and between positions in a three-man crew. While the captain has relatively low load levels throughout the day, the mate experiences high force (up to 30kgf), dynamic exertions while pulling the crab pots from the water up into the boat and high loads (20-40kgf) during the loading (morning) and unloading (evening) of the boat, while the third man experiences static awkward postures (forward flexed postures held for up to five minutes at a time) as he sorts and packs the crabs. This analysis has rendered a number of potential opportunities for ergonomic intervention - a focus of on-going research.