Structural and Potentially Modifiable Anthropometric Traits in Professional Kenyan and European Long-Distance Runners: A Cross-Sectional Study

Background: East African runners, particularly from Kenya, have long dominated long-distance running, whereas highly trained European runners represent an appropriate comparison population to investigate structural and potentially modifiable anthropometric characteristics. Objective: To compare structural and modifiable anthropometric traits between professional Kenyan and European long-distance runners and to investigate the relationship between local muscularity and skeletal robustness. Methods: A total of 52 male marathon runners (32 Kenyan and 20 European) were assessed according to the International Society for the Advancement of Kinanthropometry (ISAK) protocol. Participants were 27.2 ± 5.2 years with a BMI of 18.4 ± 1.1 kg·m−2 and a marathon time of 02:09:26 in the Kenyan group, and 30.9 ± 4.9 years, BMI 21.1 ± 2.1 kg·m−2, and marathon time of 02:18:31 in the European group. Corrected girths were calculated to explore correlations between skeletal breadths and muscularity. Results: European runners exhibited significantly greater body mass, sitting height, girths, skeletal breadths, and muscle mass compared to Kenyan runners (p < 0.05), with large to very large effect sizes. In contrast, Kenyan runners showed lower adiposity and more linear body proportions, including a lower Cormic index and higher intermembral index. Differences in segment lengths were generally limited. Principal component analysis showed clearer group separation for modifiable than structural traits. Significant positive correlations were observed between humeral breadth and corrected arm girth (r = 0.41, p = 0.002), femur breadth and corrected thigh girth (r = 0.66, p < 0.001), and bimalleolar breadth and corrected calf girth (r = 0.72, p < 0.001). Conclusions: These findings suggest that Kenyan long-distance runners exhibit a lighter and more linear anthropometric profile than their European counterparts, whereas European runners display greater skeletal robustness and musculoskeletal development. Furthermore, local muscularity may be partly associated with underlying skeletal robustness.