BACKGROUND: Optimal seatback angles for automobile drivers' seats have been investigated based on comfort and back muscle activities; however, radiology supported evidences are scarce.
OBJECTIVE: The aim of this study was to evaluate optimal range of the seatback reclining regarding torso angles for an automobile driver's seat to preserve lumbar lordosis.
METHODS: Thirty-one healthy volunteers were recruited among five body type categories. Lateral lumbar spine X-rays were obtained for the neutral sitting posture without seatback (reference), and with reclining angles of 23∘ to 33∘ by 2∘ intervals. The Cobb angles for the L1-L4, L4-S1, and L1-S1 segments were measured.
RESULTS: The Cobb angle for L4-S1 was nearest to the reference (18.74 ± 1.57∘, mean ± standard error mean) at reclining angles of 29∘ and 31∘ (14.51 ± 1.41∘ and 14.47 ± 1.43∘, respectively). The Cobb angle at L4-S1 between reclining angles of 27∘ (12.02 ± 1.31∘) and 29∘ (14.51 ± 1.41∘) were significantly different (p< 0.001). Tall men showed relatively preserved lordosis angles at all reclining angles. Fat men and short women demonstrated prominent loss of lordosis with excessively kyphotic L1-L4 segment.
CONCLUSIONS: Reclining angles of 29∘ to 31∘ revealed to be optimal for preserving lordosis at the L4-S1 segment. Individualized healthcare-related guideline for driver's seat adjustment setting is necessary.