A lot of your examples were running college level mileage when they were in high school. This can be said for a lot of high school boys as well. Some of the kids that improve the most in college are the ones who were running fast off of lower mileage in high school.
Is this actually proven, or is it just something that sounds true and it’s easy to find a few good examples to back it up?
It’d be interesting to see the high school mileage of the top 100 finishers at XC nationals for the last 10 years. I imagine someone with a little finding could do the surveys and get a fair amount of that information.
There are a number of studies out there (most dealing with the female Triad: amenorrhea, osteoporosis, and disordered eating).https://orthopaedia.com/page/Stress-Fractures-Female-Athletic-Triad#:~:text=%20Stress%20Fractures%20and%20the%20Female%20Athletic%20Triad,classically%20present...%204%20Key%20Terms.%20%20More%20
But it basically comes down to this: a girl needs a little bit of fat in order for their body to signal it is time to grow. Girls will not start their periods until they have a little extra chub. The reason girls overall tend to start their periods younger today than historically is because more kids are fatter at a young age. Young girls who are running a lot of mileage and are 10% below the average weight for their height, typically won't start their period until later (this is the number one risk factor for stress fractures later on). Growing requires an awesome amount of calories and calcium to make those bigger bones. When those ingredients are not around because they are burning them up in their runs and not eating enough to make up for it, they end up with low bone mineral density (and that stays with them into adulthood, as 98% of BMD is attained by the time a person is 19). Once the bones are developed, it becomes important to maintain sufficient caloric and calcium intake (so that you are not stealing calcium from your bones) and getting sufficient sleep to allow your body to repair itself.
According to William Roberts, MD who writes articles for Runner's World, stress fractures occur in two categories:
1. Training volume and intensity that is too high for the bone and muscle strength to support the activity
2. Inadequate energy availability to support the bone mineral density needed to tolerate the stress and strain of the training volume