Beyond somatotype categories: composition-based clustering of body types in young adults

Abstract

Background and aims: Somatotype analysis classifies individuals into 13 categories based on unique combinations of the three principal components: endomorphy, mesomorphy, and ectomorphy. This study aimed to examine sex-related differences and intra-category variability within somatotype classifications, and to characterize body composition patterns in the general population.

Methods: Anthropometric data were collected from 185 males and 156 females aged 18-40 years to estimate somatotype, fat mass index (FMI), and skeletal muscle index (SMI). Sex differences were evaluated with Hotelling's T² and chi-square tests, while within-category morphological dispersion was quantified as Euclidean distances from centroids. K-means clustering on FMI and SMI identified Low, Medium, and High groups, and somatotype distributions across clusters were compared using chi-square and binomial tests.

Results: Men exhibited an Endomorphic-Mesomorph somatotype, whereas women displayed an Mesomorph-Endomorph profile. Hotelling's T² test confirmed significant sex differences in somatotype centroids (p < 0.001), and chi-square analyses showed strong associations between sex and somatotype categories (p < 0.001). Within-category morphological dispersion was significant in most groups, with males showing greater overall variability than females (p = 0.004). K-means clustering of FMI and SMI identified Low, Medium, and High groups, with somatotype distributions differing significantly across clusters (p < 0.001); a clear predominance of a single somatotype category was observed in the Medium FMI cluster of males (Endomorphic-Mesomorph, 76.8%, p < 0.001) and in the High SMI cluster of males (Endomorphic-Mesomorph, 67.5%, p = 0.019).

Conclusion: These findings highlight pronounced sex-related differences, considerable intra-category variability, and distinct body composition patterns across somatotypes in the general population. Notably, although individuals classified within the same somatotype can still present heterogeneous body shapes, the Endomorphic-Mesomorph profile distinctly characterizes males with moderate fat mass and higher muscle mass.

Keywords: ISAK; anthropometry; body composition; heath and carter; kinanthropometry.

Graphical abstract

FIGURE 1

Somatotype distribution of males (left) and females (right) on the somatochart, classified by somatotype categories. Each dot represents an individual, color-coded by category, while black crosses indicate the centroid of each category. The shaded area represents the somatochart reference frame. BE (Balanced Ectomorph), BEn (Balanced Endomorph), BM (Balanced Mesomorph).

FIGURE 2

Somatotype distribution of males (left panels) and females (right panels) on the somatochart, colored by k-means clusters based on fat mass index (FMI) on the top and skeletal muscle index (SMI) on the bottom. Each dot represents an individual, with colors indicating Low (blue), Medium (yellow), and High (red) clusters. BE (Balanced Ectomorph), BEn (Balanced Endomorph), BM (Balanced Mesomorph).

FIGURE 3

Radial plots showing the distribution of participants across somatotype categories within Low, Medium, and High fat mass index (FMI) (kg/m²) clusters in males (top) and females (bottom). Each bar represents the proportion (in %) of individuals within a cluster, while absolute counts with percentages are reported as external labels. The plots are scaled to a maximum radius of 80% to improve readability. CEN (Central), BE (Balanced Ectomorph), BEn (Balanced Endomorph), BM (Balanced Mesomorph), E-En (Ectomorph–endomorph), Ec-En (Ectomorphic–Endomorph), Ec-M (Ectomorphic–Mesomorph), En-E (Endomorphic–Ectomorph), En-M (Endomorphic–Mesomorph), M-E (Mesomorph–Ectomorph), Mc-E (Mesomorphic–Ectomorph), M-En (Mesomoph–Endomorph), and Mc-En (Mesomorphic–Endomorph). *** = p < 0.001.

FIGURE 4

Radial plots showing the distribution of participants across somatotype categories within Low, Medium, and High skeletal muscle index (SMI) (kg/m²) clusters in males (top) and females (bottom). Each bar represents the proportion (in %) of individuals within a cluster, while absolute counts with percentages are reported as external labels. The plots are scaled to a maximum radius of 80% to improve readability. CEN (Central), BE (Balanced Ectomorph), BEn (Balanced Endomorph), BM (Balanced Mesomorph), E-En (Ectomorph–Endomorph), Ec-En (Ectomorphic–Endomorph), Ec-M (Ectomorphic–Mesomorph), En-E (Endomorphic–Ectomorph), En-M (Endomorphic–Mesomorph), M-E (Mesomorph–Ectomorph), Mc-E (Mesomorphic–Ectomorph), M-En (Mesomoph–Endomorph), and Mc-En (Mesomorphic–Endomorph). * = p < 0.05.

FIGURE 5

Heatmap representation of the somatotype distribution for males (left) and females (right) on the somatochart. Each square represents the density of participants within that region, color-coded according to their muscle-to-fat ratio, with warmer colors (yellow to red) indicating higher values. The white triangular boundary delineates the somatochart axes: BE (Balanced Ectomorph), BEn (Balanced Endomorph), BM (Balanced Mesomorph). The muscle-to-fat ratio was calculated as the ratio between skeletal muscle mass (kg) and fat mass (kg).