Objective: This study investigated injury outcomes and body
kinematics in obese occupants exposed to frontal impacts while seated in
reclined postures. With increasing interest in non-traditional seating
configurations and a growing population of obese vehicle occupants, the
objective was to evaluate how seat stiffness and restraint features influence
injury patterns and whole-body excursions.
Methods: Nine obese post-mortem human surrogates (PMHS; mean age: 64
years, stature: 1.70 m, body mass: 102 kg, BMI: 35 kg/m2) were tested
under frontal impact conditions simulating a delta-V of 50 kph. All specimens
were seated on a spring-controlled seat with a 45° reclined seatback and
restrained by a three-point belt system with pretensioner and load limiter.
Three configurations were evaluated: (1) stiffer seat, (2) softer seat, and (3)
stiffer seat with a knee bolster 100 mm from the knees. Each subject underwent
one test. Whole-body kinematics were captured using a VICON motion analysis
system, and injury outcomes were assessed through radiographs, CT imaging, and
autopsy, with severity classified by Maximum Abbreviated Injury Scale (MAIS) and
Injury Severity Score (ISS).
Results: Softer seats produced substantially greater downward (+Z)
pelvic displacement compared with stiffer seats. The knee bolster effectively
reduced both downward and forward excursions of the lower torso. Rib cage and
pelvic injuries were most frequent, with the highest severity observed in softer
seat tests. Mean ISS values were: STIFF—27, 13, 27; SOFT—34, 27, 14;
STIFF-KB—22, 0, 13.
Discussion: Reduced seat stiffness combined with increased occupant
mass contributed to greater excursions and anterior torso injuries, whereas the
knee bolster mitigated excursion and injury severity. Findings are limited by
sample size and test conditions; broader evaluation with production seats is
needed to confirm trends and support countermeasure design.
