Brenda Martinez is extremely talented, and extremely hard working
From:
http://fittish.deadspin.com/why-the-800-comes-down-to-hunters-and-the-hunted-1699308516
"She reaches a peak of 80 miles per week and told RunnersWorld she’s upped her long run to 14 miles. Of course, that’s during base training. Closer to 800 competition, she’ll drop down to 70 to 75 miles per week, which is still nearly double what most sprint-based programs call for. "
....
"She’s the Tina Turner of the 800, is Martinez. She likes to do things nice and rough, e.g. 10 miles at 5:55 pace, mile repeats in 4:50, and this killer— eight x 1000 meters in 2:50 to 3:00 minutes, with three minutes recovery between each, and a fast 400 at the end of the workout for good measure. "
I'm going to go out on a limb and suggest this is vastly more important than how her body tissues are distributed, or how many planks or crunches she does.