Effect of Varying Child Restraint System Seatback Angle on Spinal Loading of 1.5 YO and 3 YO PIPER Human Body Models in Frontal Impacts

S. Tushak, M. Valdano, J. Kerrigan, F.J. López-Valdés

Eng Vol. 7, nº. 2, pp. 61

Summary:

This computational study examined how variations in the seatback angle of two generic child restraint systems (CRSs) affect spinal loading in young occupants (1.5 YO and 3 YO) during frontal impacts, performed according to the specifications included in UNECE R129. CRS seatback angle dictates torso recline, which in turn influences head, chest, and spine kinematics and loading. While manufacturers typically recommend 30–45° for rear-facing CRSs and an upright position for forward-facing CRSs, little is known about the biomechanical implications of deviating from these guidelines. Using PIPER human body models representing a 1.5-year-old in a rear-facing CRS and a 3-year-old in a forward-facing CRS, simulations were performed under UN-R129 frontal impact conditions. The seatbacks were rotated 5° and 10° more upright or reclined relative to the nominal angle, with occupants restrained by a five-point harness and CRSs secured with ISOFIX, top tether, or three-point belt. The results showed that reclined configurations generally increased the predictions of spinal loading (forces and/or moments) given by the PIPER model, while nominal or more upright angles reduced loads, particularly in the lumbar spine of the 3-year-old model. Overall, the study highlights how computational tools can guide CRS design improvements to optimize spinal protection and enhance child safety beyond current regulatory requirements.

Spanish layman's summary:

Simulaciones UN R129 con HBM PIPER 1,5 años (a contramarcha) y 3 años (a favor) indican que reclinar el respaldo aumenta cargas cervicales/lumbares; nominal/más vertical las reduce (especialmente lumbar en 3 años).

English layman's summary:

PIPER 1.5YO (rear-facing) and 3YO (forward-facing) HBMs in UN R129 frontal simulations: study of how seatback angle changes affect cervical and lumbar loads.

Keywords: child occupant; forward-facing; rear-facing; seatback angle; cervical spine; lumbar spine; PIPER

JCR-JIF Impact Factor and WoS quartile: 2,400 - Q2 (2024)

DOI reference: https://doi.org/10.3390/eng7020061

Published on paper: February 2026.

Published on-line: February 2026.

Citation:
S. Tushak, M. Valdano, J. Kerrigan, F.J. López-Valdés, "Effect of Varying Child Restraint System Seatback Angle on Spinal Loading of 1.5 YO and 3 YO PIPER Human Body Models in Frontal Impacts", Eng, Vol. 7, nº. 2, pp. 61, February 2026. [Online: February 2026] doi: 10.3390/eng7020061