Lumbar spinal loads and lumbar muscle forces evaluation with various lumbar supports and backrest inclination angles in driving posture

Purpose The low back pain of professional drivers could be linked to excessive lumbar load. This study aims at developing a musculoskeletal model to study the lumbar spinal loads and lumbar muscle forces of the human body in driving posture, so as to contribute to a better understanding of low back pain and to improve the design of vehicle seats. Methods A standing musculoskeletal model, including limbs, head and neck, that can reflect several activities of daily living was established based on the Christophy spine model. The model was then validated by comparing the calculated lumbar loads and muscle forces to the experimental data in the previous studies. Referring to radiology studies, the musculoskeletal model was adjusted into different driving postures with several different lumbar supports (0, 2 and 4 cm) and inclinations of the backrest (from 23° to 33°, by 2° intervals). The lumbar biomechanical load with various lumbar supports and backrest inclination angles was calculated. Results The results showed that the overall lumbar spinal load and lumbar muscle force with 4 cm lumbar support were reduced by 11.30 and 26.24%. The lumbar spinal loads and lumbar muscle forces increased first and then decreased with the increase in backrest inclination angles from 23° to 33°. The lumbar biomechanical load varied slightly with the backrest inclination angles from 29° to 33°. Conclusions There are two findings: (i) the lumbar spinal loads at the L3–L4, L4–L5 and L5–S1, and lumbar muscle forces decreased obviously with the 4 cm lumbar support, while the seat cushion inclination angle was set to 10°. (ii) The recommended backrest inclination angles are 29° to 33° with a 10° seat cushion to the horizontal, which can keep a low level of the lumbar spinal loads and lumbar muscle forces. This study could be used to explain the association between drivers’ sitting posture and the lumbar load change, and provide a reference for the prevention of low back pain.