Photo: Jonathon Kambouris

20 of 25
Old School: Running pants must be black.

New Rule: The freshest running gear is patterned, colorful and (surprise!) flattering. How is that possible? Each of these pieces has smart details that visually slim. Now if only they could make that 10K go by faster...
From left:
Xersion, $44;
C9 by Champion, $25;