Runners understandably focus on their long runs while training for races from the 5K to marathons and ultras. Your ability to run long determines how well you run your longest races, and long runs help build the aerobic capability that carries you through races of all distances.
However, the long run also receives too much focus. I’m not going to call the long run overrated, because long runs definitely are not overrated. They’re important. But long runs are one component of a successful training plan, and building your aerobic endurance and performance requires more than getting your long run in every week.
And no, I don’t mean doing your speedwork. In fact, improving your aerobic capability requires no speedwork at all (though speedwork can certainly help your running economy, and is valuable for maximizing your race day speed).
We fixate on the length of our long runs. We fixate on the speed at which we run our speedwork. But we don’t pay much attention to the length of our regular runs, and it turns out the latter is as important (if not more important) to developing our aerobic endurance.
To briefly summarize and blow over a ton of science: