The human body changes as it becomes older. The automotive
safety community has been interested in understanding the effect of
aging on restraint performance. Recent research has been focused on
assessing the structural and material changes associated with age.
In this study, structural tissue distribution was determined using
the computed tomography (CT) scan data of more than 19,000
patients, aged 16 and up. The data consisted of subcutaneous fat
cross-sectional area, visceral fat cross-sectional area, and
trabecular bone density taken at each vertebral level. The data was
quantified as a function of five age groups with the youngest group
defined as 16-29 years old and the oldest group as 75 and up. An
additional analysis stratified on gender was carried out.
Overall, visceral fat increased with age. Compared to the 16-29
group, the visceral fat measured at the L1 level was 1.97 in the
30-44 group, 2.55 in the 45-59 group, 3.33 in the 60-74 group and
3.21 times greater in the 75+ group. Subcutaneous fat also
increased with age up to the 60-74-year-old group. The subcutaneous
fat measured at L1 level was 1.34 in the 30-44 group, 1.39 in the
45-59 group, 1.38 in the 60-74 group and 1.09 times greater in the
75+ group than in the 16-29 group. A significant association
between trabecular bone density and age was found. Trabecular bone
density in Hounsfield units (HU) decreased as a function of age, by
2.57*age + 0.0056*age₂ for females and 2.57*age + 0.0082*age₂ for
males.
Gender differences were also observed. Females had 1.43 times
more subcutaneous fat and 1.10 times higher trabecular bone density
than males at L1, while males had 1.88 times more visceral fat than
females. Females gained more subcutaneous fat at L1 as they
increased in age up to the 45-59 group and then progressively lost
subcutaneous fat. Males and females gained more visceral fat at L1
as they aged up to the 60-74 group. Both consistently lost bone
density at L1 as they grew older.
The data was also analyzed for a male subgroup approximating the
height and weight of a 50th percentile male dummy. Visceral fat
increased with age while trabecular bone density decreased.
There was an overall-trend for an increase in subcutaneous fat
with age. The results obtained in this study provide insight on the
quantified effect of bone and fat distribution as a function of
age, gender, and vertebral level. Fat and bone distribution needs
to be considered in human mathematical models used to develop
safety countermeasures for the older population.
