In vehicle collisions, the lap belt should engage the anterior superior iliac spine (ASIS). In this study, threedimensional (3D) shapes of bones and soft tissues around the pelvis were acquired using a computed tomography (CT) scan of 10 male and 10 female participants wearing a lap belt. Standing, upright sitting, and reclined postures were scanned using an upright CT and a supine CT scan system. In the upright sitting posture, the thigh height was larger with a higher BMI while the ASIS height did not change significantly with BMI. As a result, the height of the ASIS relative to the thigh (ASIS-thigh height) became smaller as the BMI increased. Because the thigh height of females was smaller than that of males, the ASIS-thigh height was larger for females than for males. As the ASIS-thigh height was larger, the overlap of the lap belt with the ASIS increased. Thus, the lap belt overlapped more with the ASIS for the females than for the males. The abdomen outer shape is characterized by the trouser cord formed valley, the torso/thigh junction, and the anterior convexity formed between them depending on the adipose tissues. The abdomen outer shapes changed from the standing, the reclined posture to the upright sitting posture. In the reclined sitting posture, the lap belt is positioned upward and rearward relative to the ASIS, and the overlap of the lap belt with the ASIS was smaller compared to the upright posture.
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