It's certainly possible to injure yourself with your own movements but aside from something already being very wrong somewhere you basically have to be a martial artist capable enough of overcoming protective reflexes in a highly unintuitive and wrong way: If you say, throw a punch but don't have the muscle/nervous control to also stop it you could easily damage something once your joints reach the end of their travel, fascia by default act like a non-newtonian fluid, roughly speaking the more sudden you move the more they resist, avoiding run-away momentum that could cause that kind of damage. You can relax them but generally speaking your body won't let you do it, wont trust the orders you give it, unless you have the control to do it safely -- and that includes a tranquil mind. And if you manage to do it wrong you will do that exactly once, and never again, at least if you have a shred of common sense. At that point you can only hope that you're not actually good at being fast.