There is a great amount of analysis at ThunderPlace studying what is occurring, and even by some members that are in the medical field. The leading theory is micro-tears. As far as injury is concerned it is not the likely result. The vast majority do not experience injury, and the ones that do usually admit they have overdone it and did not follow established safety methods. The mainstream medical establishment have been incorrect countless times throughout the years. Why so certain they can't be wrong again.