I just came across this article about Lara Tamsett, the 20-year old Australian National Champion at 10,000m, who only trains once a day. It is filled with sage training advice for young runners. A couple snippets:
"I try to do one good session a day and then rest. It's enough until I start plateauing, then I might step it up. The key to progress is staying injury-free.
"I'm careful not to get sucked into other people's training because the reps can become competitive.
It's incredibly hard to show restraint when things are going well in your training. The riskiest time is when you feel so good that you decide to do more. She continues:
"I think one of my greatest strengths is that I under-train."
This is my favorite line in the article, because it begs the question: is she really under-training? By whose standards? Who's to say that most athletes at her age and stage of development aren't over-training?
It may be true that, as Steve Monaghetti states in the article, "There has never been a distance runner who has reached the highest level without training twice a day." But that doesn't make it the case that there's never been a distance runner who reached the highest level without training twice a day in their teens.
I believe a lot of athletes--especially those who are most competitive, passionate, and successful at a young age--rush into training too much in the quest for short-term awards and accolades. This can lead to over-training, burnout, eating disorders, and ultimately, injury and illness.
Lara Tamsett is right that the key to progress is staying injury-free. It requires discipline, restraint, a long-term view, and a little bit of luck. It might also require a change in what we define as "under-training".