Belt-positioning booster seats (BPBs) help promote proper seat belt fit for
children in vehicles. The effectiveness of BPBs depends on occupant posture,
which can be influenced by BPB design features. This study aimed to
quantitatively describe how children's postures naturally change over time in
BPBs, using pressure mats. Thirty children aged 5 to 12 participated in two
30-minute trials using randomly assigned seating configurations. Five
configurations were studied by installing two backless BPBs in vehicle captain’s
chairs, varying booster profile (high, low, or no BPB) and armrest presence
(with or without BPB/vehicle seat armrests). TekScan 5250 pressure mats were
placed on the seating surfaces. Children began in an ideal reference posture,
and center of force (COF) data were collected continuously. Additional
observations on posture, behavior, and comfort were periodically collected.
Mixed models, including effects of seating configuration, time, and volunteer
characteristics, were used to explore changes in COF position from the reference
position with time. Children assumed a variety of postures. Over time, children
showed a statistically significant forward COF shift of 2.5 cm from the initial
posture across all trials (p = 0.003). No significant differences were found in
the average COF position or translation between seating configurations in the
fore-aft (x) or inboard-outboard (y) directions. However, the maximum and
cumulative COF translation in the x-direction was significantly influenced by
booster profile, with high-profile configurations resulting in the least amount
of translation. Children tended to slouch over time, as evidenced by an average
forward COF translation of 2.5 cm over thirty minutes. These findings were
supported by video footage and posture data. Trends toward forward COF
translation were most apparent in low-profile and no booster configurations.
Such changes in booster occupant postures can imply increased injury risk,
specifically associated with submarining as evaluated in previous computational
investigations. Future research should examine these trends in real-world
driving environments and assess how specific BPB design elements may support
better long-term posture during vehicle travel.