The American population is getting heavier and automated vehicles will
accommodate unconventional postures. While studies replicating mid-size and
upright fore-aft seated occupants are numerous, experiments with post-mortem
human subjects (PMHS) with obese and reclined occupants are sparse. The
objective of this study was to compare the kinematics of the head-neck, torso
and pelvis, and document injuries and injury patterns in frontal impacts. Six
PMHS with a mean body mass index of 38.2 ± 5.3 kg/m2 were equally
divided between upright and reclined groups (seatback: 23°, 45°), restrained by
a three-point integrated belt, positioned on a semi-rigid seat, and exposed to
low and moderate velocities (15, 32 km/h). Data included belt loads, spinal
accelerations, kinematics, and injuries from x-rays, computed tomography, and
necropsy. At 15 km/h speed, no significant difference in the occupant kinematics
and evidence of orthopedic failure was observed. At 32 km/h speed, the primary
difference between the cohorts was significantly larger Z displacements in the
reclined occupant at the head (190 ± 32 mm, vs. 105 ± 33 mm p < 0.05) and
femur (52 ± 18 mm vs. 30 ± 10 mm, p < 0.05). All the moderate-speed tests
produced at least one thorax injury. Rib fractures were scattered around the
circumference of the rib-cage in the upright, while they were primarily
concentrated on the anterior aspect of the rib-cage in two reclined specimens.
Although MAIS was the same in both groups, the reclined specimens had more
bi-cortical rib fractures, suggesting the potential for pneumothorax. While not
statistical, these results suggest enhanced injuries with reclined obese
occupants. These results could serve as a data set for validating the response
of restrained obese anthropometric test device (ATDs) and computational human
body models.
