Quantifying Naturalistic Changes in Occupant Postures in Belt-Positioning Booster Seats Utilizing Pressure Mats

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.