Biomechanics model to predict the compressive force exerted on L5/S1 in manual material handling among young workers (18-24 years old)

Several epidemiological studies have investigated manual material-handling as one of the ergonomics risk factors for potentially developing musculoskeletal disorders (MSDs), especially lower back pain. This study aimed to predict the compressive force (CPF) at L5/S1 when Thai youth performed lifting tasks using the biomechanics model. In addition, the relationship between individual characteristics, load weight, lifting frequency, and rating of perceived exertion with the compressive force was determined and compared the CPF at L5/S1 between males and females. Sixty healthy Thai workers aged from 18 to 24 evenly divided by gender perform repetitive lifting tasks with five different lifting frequencies (1, 2, 4, 6, and 12 lifts/minute) in the sagittal plane, following the National Institute for Occupational Safety and Health (NIOSH) lifting technique. The relationship was quantified by multiple linear regression. Results indicated that the load weight had a major impact on the compressive force at L5/S1 joint both for the lift origin and destination. In term of lift origin, load weight, trunk angle, body mass index (BMI), and rating of perceived exertion (RPE) significantly affected the CPF exerted on L5/S1 for the lift origin (p<0.001). In part of the CPF for the lift destination, load weight, trunk angle, forearm angle, BMI, lifting frequency, and gender significantly influenced (p<0.001). In addition, the CPF at L5/S1 of for the lift origin and destination of males exceeded that of females at every lifting frequency. These findings may be used for determining optimal lifting conditions for young workers, taking into account employee skills and limitations, without detrimentally affecting their health.