I've read that one of the ways that exercise increases muscle mass is through micro-lesions that your body goes on to repair. Not my expertise at all, but it's a thing, it seems. Googling now only shows content farm generated ads for fitness, unfortunately.
I've also heard that the growth mechanism is muscle tissue responding to damage caused by strength training / use. However, the result is not scar tissue that is "tougher". The result is more muscle tissue, of the same toughness that was there before, just capable of doing more work by virtue of a larger amount present.
Compare this to true trauma to the tissue, which results in scarring. Scar tissue may be "tougher" (less pliable) but it's not contributing to additional work. A better analogy might have been that broken bones grow back stronger, though even that requires that they are set right and have an appropriate amount of recovery time, which to continue the analogy, might be therapy needed to not be so brittle in the first place.
