Total body and regional surface area: Quantification with low-cost three-dimensional optical imaging systems

OBJECTIVES

Body surface area (SA) is a widely used physical measure incorporated into multiple thermophysiology and evolutionary biology models currently estimated in humans either with empirical prediction equations or costly whole-body laser imaging systems. The introduction of low-cost 3D scanners provides a new opportunity to quantify total body (TB) and regional SA, although a critical question prevails: can these devices acquire the quality of depth information and process this initial data to form a mesh that has the fidelity needed to generate accurate SA estimates?

MATERIALS AND METHODS

This question was answered by comparing SA estimates calculated using images from four commercial 3D scanners in 108 adults to corresponding estimates acquired with a whole-body laser system. This was accomplished by processing initial mesh data from all devices, including the laser system, with the same universal software adapted specifically for repairing mesh gaps, identifying landmarks, and generating SA measurements.

RESULTS

TB SA measured on all four 3D scanners was highly correlated with corresponding laser system estimates (R² s, 0.98-0.99; all p < 0.001) with some small but significant mean differences (-0.19 to 0.06 m² ); root-mean square errors (RMSEs) were small (0.02-0.03 m² ); and significant bias was present for one device. Qualitatively similar results (e.g., R² s, 0.78-0.95; mean Δs, -0.05 to 0.02 m² ; RMSEs, 0.01-0.03 m² ) were present for trunk, arm, and leg SA comparisons.

DISCUSSION

The current study observations demonstrate that low-cost and practical 3D optical scanners are capable of accurately quantifying TB and regional SA, thus opening new opportunities for evaluating human phenotypes and related physiological characteristics.

Population history and ecology, in addition to climate, influence human stature and body proportions

Worldwide variation in human stature and limb proportions is widely accepted to reflect thermal adaptation, but the contribution of population history to this variation is unknown. Furthermore, stature and relative lower limb length (LLL) show substantial plastic responses to environmental stressors, e.g., nutrition, pathogen load, which covary with climate. Thus ecogeographic patterns may go beyond temperature-based selection. We analysed global variation in stature, sitting height and absolute and relative LLL using large worldwide samples of published anthropometric data from adult male (n = 571) and female (n = 268) populations in relation to temperature, humidity, and net primary productivity (NPP). Population history was modeled using spatial eigenvector mapping based on geographic distances reflecting the hypothesized pattern for the spread of modern humans out of Africa. Regression models account for ~ 50% of variation in most morphological variables. Population history explains slightly more variation in stature, sitting height and LLL than the environmental/climatic variables. After adjusting for population history, associations between (usually maximum) temperature and LLL are consistent with Allen's "rule" and may drive similar relationships with stature. NPP is a consistent negative predictor of anthropometry, which may reflect the growth-limiting effects of lower environmental resource accessibility (inversely related to NPP) and/or pathogen load.

Ecogeographic patterns in fetal limb proportions

OBJECTIVES

Humans generally comply with the ecological rule of Allen (1877), with populations from tropical environments exhibiting body proportions in which limb segments are long relative to trunk height compared to temperate groups. This study tests whether ecogeographic differences in intralimb proportions are identifiable among two modern fetal samples of differing ancestry.

MATERIALS AND METHODS

Data are derived from radiographic measurements of long bone diaphyseal length and crown-heel length (CHL) of contemporary, spontaneously aborted fetuses of African Americans ("black") of assumed African (tropical) ancestry and European Americans ("white") of assumed European (temperate) ancestry (n = 184). Population individual limb elements, brachial, and crural indices are compared via analyses of covariance (ANCOVA). Potential patterns of divergent allometric growth are quantified through principal components analysis (PCA).

RESULTS

African ancestral distal limb elements were consistently, albeit slightly, longer than those of European ancestry, relative to CHL. None of the ANCOVA interactions with ancestry are statistically significant for limb indices. The radius was the only single element that displayed a statistically significant ancestry effect (p = 0.0435) equating to a 1 mm difference. PCA highlights that upper limbs demonstrate negative allometry and lower limbs demonstrate positive allometry with sample-specific multivariate growth patterns being nearly identical. Differences in growth allometry late in gestation make little contribution to observed differences in adult limb proportions.

DISCUSSION

No statistically significant ecogeographic patterns were appreciated among intralimb proportions between these groups during the fetal period. This study contributes to a greater appreciation of phenotypic plasticity, ecogeographic variation in ontogeny, and the evolution of modern human diversity.