At the 1960 summer Olympics, three New Zealand underdogs took home four medals. All three men were coached by a milkman that never went to college.
The Europeans and Americans, favorites to win, had prepared with the most grueling workouts their university-educated coaches could devise. But they lost.
In 2012, John Davis published a booklet describing the training methods of that milkman, Arthur Lydiard.
The Basics of Basic Training Principles is my summary of Davis' book:
Why should you care?
Lydiard's approach—build a foundation first, pay attention to recovery, finish with speed—informed and empowered the generations that followed. According to Steve Magness, this made Lydiard the "father of modern endurance training".
Although most mountain athletes try to out-exercise each other in pursuit of better performance, studying a more mature sport might be more effective.
Basic Training Principles is a good place to start.