Three Brothers Share A Family Sport, A Nonstop Marathon

Riddle: Three Brothers share a family sport, a nonstop marathon. The oldest one is fat and short And trudges slowly on. The middle brother's tall and slim, and keeps a steady pace The youngest runs just like the wind, going swiftly through the race "He's young in years, we let him run," the other brothers say. "Though he is surely number one, he's also second in a way. What are we?