I have seen reports of improvements in old muscle injuries with PRP injections, or with PRP injections combined with a stem cell preparation. However, I certainly wouldn't get my hopes up.
Thanks for taking the time to answer this Michael. I didn't know about the PRP injections. Is there any specific treatment using these two methods which targets muscle regeneration? Are there any studies or experiments involving these? I'm aware that anything like this will take 5 - 10 years to fully develop.
I posted a blog here with useful info. The rest is easy to find by searching the sports medicine literature. As I said though, the good clinical studies are quite rare at this point.