Geoffrey Kirui won the 121st Boston Marathon on Sunday as Kenyans dominated the men's and women's races.
The 24-year-old pulled away from American Galen Rupp in the last two miles of the race to win the 24-mile race in an unofficial time of 2 hours nine minutes and 37 seconds.
Aside from the Kenyan's impressive time in soaring temperatures in Boston, Kirui's extraordinary leg definition left a number of spectators stumped.
Ross Tucker, who writes for Science of Sport, wrote on Twitter that he had never seen an athlete with horizontal musculature in their quadriceps like that of Kirui's.
Kirui's fellow countryman Eliud Kipchoge, who won Olympic gold in 2008, also showed off the same unique muscle definition.
"Olympic champ Kipchoge & #bostonmarathon winner Kirui showing those horizontal muscle striations. I’d never seen this before these pictures," wrote Tucker.