Muscle‐tendon architecture in Kenyans and Japanese: Potential role of genetic endowment in the success of elite Kenyan endurance runners

Abstract

Aim:The specificity of muscle-tendon and foot architecture of elite Kenyan middle-and long-distance runners has been found to contribute to their superior running performance. To investigate the respective influence of genetic endowment and training on these characteristics, we compared leg and foot segmental lengths as well as muscle-tendon architecture of Kenyans and Japanese males (i) from infancy to adulthood and (ii) non-athletes versus elite runners. Methods:The 676 participants were divided according to their nationality (Kenyans and Japanese), age (nine different age groups for non-athletes) and performance level in middle-and long-distance races (non-athlete, non-elite and elite adult runners). Shank and Achilles tendon (AT) lengths, medial gastrocnemius (MG) fascicle length, pennation angle and muscle thickness, AT moment arm (MA AT ), and foot lever ratio were measured.Results: Above 8 years old, Kenyans had a longer shank and AT, shorter fascicle, greater pennation angle, thinner MG muscle as well as longer MA AT , with lower foot lever ratio than age-matched Japanese. Among adults of different performance levels and independently of the performance level, Kenyans had longer shank, AT and MA AT , thinner MG muscle thickness, and lower foot lever ratio than Japanese. The decrease in MG fascicle length and increase pennation angle observed for the adult Japanese with the increase in performance level resulted in a lack of difference between elite Kenyans and Japanese. Conclusion:The specificity of muscle-tendon and foot architecture of elite Kenyan runners could result from genetic endowment and contribute to the dominance of Kenyans in middle-and long-distance races. K E Y W O R D S endurance running, ethnicity, foot structure, gear ratio, growth, ultrasonography T A B L E 1 Anthropometric parameters and sample size for Kenyan and Japanese non-runners Age (years) Height (cm) Body mass (kg) Sample size (n)

Muscle morphology and architecture of the medial gastrocnemius between typically developing children with different ancestral backgrounds

“…Normalized tendon length of the MG muscle was 7-11% longer in both Hindustani (South Asian) and Marron (African) children, compared to Javanese Southeast Asian) children. This is in line with a recent study, where differences in tendon length between Japanese (East Asian) and Kenyan (African) children were found, already at the age of 4 years old (Kunimasa et al ., 2022). Similar percentages of difference in Achilles tendon length (i.e., ≈10% longer tendon lengths) between Kenyan (African) compared to Japanese (East Asian) adult runners has been reported (Kunimasa et al ., 2014; Sano et al ., 2015).…”

“…Maroon (African) children were significantly taller with longer lower leg lengths compared to Javanese (Southeast Asian) and Hindustani (South Asian) children. Similar results were found in a recent study where lower leg length in Kenyan (African) children was longer compared to Japanese (East Asian) children, while there was no difference in body weight (Kunimasa et al ., 2022). Lee et al .…”

“…(2014) investigated similar age groups, current data showed no differences in body weight and calf circumference between ancestral groups. Longer leg lengths were also found in a recent study of Kunimasa et al . (2022) in children with African compared to East Asian ancestry.…”

“…To the best of our knowledge, only two previous studies compared muscle morphology and architecture between children of different ancestry (Kunimasa et al ., 2022). Song et al (2002) reported smaller total muscle volume of both the upper and lower limbs in East Asian and Caucasian children compared to children of African descent (Song et al ., 2002).…”

“…(2022), who recently reported smaller muscle thickness for the medial gastrocnemius (MG) in Kenyan (African) children compared to Japanese (East-Asian) children (Kunimasa et al ., 2022). The latter study also observed shorter fascicle and longer Achilles tendon lengths, with no differences in pennation angle, in the Kenyan compared to Japanese children (Kunimasa et al ., 2022). Most of these morphological and architectural differences were already observed at an age of 4 years.…”