2nd part of the tweet:
https://twitter.com/SaraHall3/status/1150528785269133312
When we see the second part of the tweet, I don't see how it's event controversial. Maybe it's the part where she ran 70 mpw all throughout high school? Remember though that high school isn't where Sara Hall started running. She was an age group runner before that. She was farther along in training than most 9th graders and was able to handle more.
High mileage is a term that is largely based on perspective. I started running in 8th grade and ran about 15 miles per week. My friends who didn't run thought it was crazy, and for that reason, I thought I was a badass for running so much. Going into freshman year my coach wanted me to run 30 miles a week and I thought that was crazy. I was so proud the first time I ran 8 miles in a day because it seemed ridiculous that a person would do that. I remember my sophomore year when I made a decision to run 50 mpw I thought that I was pushing boundaries. I only ran 6 days a week, so in a year I went from being impressed with myself for running 8 miles in a single run to averaging more than 8 miles a day. I ran faster than I ever had and qualified for races that I could not have gotten into prior to that. And when I talked to the other guys in those races, I found that most of them were running 50 miles per week. I finished high school running about 65 miles per week and felt good about doing it, but that no longer felt like high mileage. I went into college running about 75 mpw and topped out in college at over 100 mpw and that was just what we did. So at what point did it become high mileage? Or did it? If I polled everyone who has posted in this thread, I don't think anyone would call 15 or 30 mpw high mileage, but I bet a few might say that 50 mpw is high mileage. Especially when they attribute it to a sophomore. Then again, others would say that 70 mpw is not high mileage. These opinions are going to be shaped by how much mileage people have ever done and what their experiences were with their highest mileages. For instance, I probably did 100 mpw 6 months or a year before I really should have. That season felt like that number just was not productive and my race times reflected that. I dropped down and ran better. But the next season when I got back to 100 mpw it was sustainable and I ran well. It no longer felt like super high mileage. It was just the routine.
Sara was great in high school and really good in college, but remember that she did suffer through some adversity. Maybe that adversity was due to mistakes in training that she learned from. I don't really know. But over the term of a long career, her build up worked. She's been very successful.
Now, if the gripe is that some people can go about building mileage in a destructive way, I will not argue against that. The methodology that some coaches and athletes use to arrive at their training can be downright stupid and unhealthy. The more training an athlete is going to do, the more careful they have to be and the more precautions they have to take. But I don't think that the point of the tweet is to say that kids should just go out the door and run a ton of mileage without thought, but rather that if a kid wants to take the next step in his or her training, it can be done without being inherently unhealthy or an inherently oppressive experience.