Looking at her vs. Sally Kipyego at the finish today , Molly even though she is tiny and really lean, shes still too muscular to be 2:19 etc. She can do pullups, even though that's sexy, too much back muscle for marathon. Muscle is a very metabolically demanding tissue the more you have the more blood flow it demands. Her butt is too muscular, good for that 10k kicking speed, maybe bad for the marathon. You have to basically look like the Kenyans - stick figures.