I’ve said before that I don’t think anyone really has the answer(s) about arm health for pitchers. There seems to be a large component that is genetic (see, e.g., Nolan Ryan’s longevity), and pitchers sometimes get injured—or not—following just about every known training regimen.
I have no medical training and am not a pitching coach. I have read everything I can and talked with a lot of folks who know more than I ever will about orthopedics and/or pitching. Having said that, for my son I have tried to keep two principles in mind: 1) When in doubt, take a conservative approach—that is, less throwing, fewer innings. And 2) the best source I know for advice on arm health that is medically knowledgeable and based on actual data are Drs. James Andrews and Glenn Fleisig. Their recommendation (from the PitchSmart guidelines) for players HS age up to 22 years old is: “Take at least 4 months off from competitive pitching every year, including at least 2-3 continuous months off from all overhead throwing.” IMO given the state of knowledge in 2018, that advice is the gold standard