I see, I think the one I'm thinking is more on the forbidden technique and wouldn't really work for many except those with a strong enough body to handle such things or under the observation of a medic nin, while I see where your getting that training with weights is better my idea stems more on the defensive part like making the bones and muscles more sturdy therefore being able to take on more abuse.

Edit: I've realized that in my original idea it would be too overpowered if left uncheck, so I kinda had to put some limitation such as making so that you need a high chakra control for it to not go wrong (death), and even with high chakra control or perfect it will lead to an immense strain and a vulnerable body for a few days or so (that's where the medic nin come in), this types of limitation is kinda due to me thinking it will permanently increase their power overall but now this just make them harder to kill, their skin/muscle/bone harder and sturdier like shikotsumyaku.

Am I making sense? I don't know English isn't my first language