Kinematics and dynamic responses of young and elderly occupants in low-speed frontal tests

Abstract

Objetive: The objective of the study was to compare the kinematics of young and elderly volunteers in low-speed frontal impacts to identify the existing differences in the motion of the head and upper spine. Method: Five young (age: 20±1.9 years old; stature: 174.6±5.4 cm; weight: 76.2±2.5 kg) and four elderly (age: 74±7.9 years old; stature: 168.7±5.6 cm; weight: 86.6±9.3 kg) relaxed volunteers were exposed to repeated non-injurious frontal impacts at 9 kmh with a maximum deceleration of 3.5 g. Test protocol was approved by the relevant Ethics Board. The test fixture consisted of a rigid seat and footrest that approximated the seating position of a car occupant. The non-force-limited, three-point seat belt was pretensioned statically prior to the tests. A three-dimensional (3D) motion capture system was used to track the trajectories of the head and selected anatomical landmarks (including C4, T1, T4 and T8) at 1,000 Hz. Other instrumentation included the 3D acceleration and angular rate of the head and the seat belt tension at three locations. Result: Younger volunteers exhibited a greater average peak forward excursion of the head center of gravity and C4 (head: 134.5±14.5 vs 116.1±6.3 mm; C4: 108.4±18.0 vs. 92.8±5.6 mm), while the peak forward excursions of the thoracic vertebrae of the elderly volunteers were higher than those observed in the younger group. Upper shoulder average belt force was slightly higher for the elderly volunteers (1195 N vs 1289 N) but lap belt forces peak values were substantially higher in the younger volunteers. Head angular rate flexion was also greater in the young group. Conclusion: These results help to identify age-related differences in the kinematics of volunteers in low-speed frontal impacts and may be used to benchmark human body models susceptible to represent occupants of different ages.