When ur diet & training r tuned in, & u reach an unbreakable plateau no matter the "tweaks" or adjustments u mak, THEN, u hav reached ur natural limit. But it takes about a yr or so after u hav reached that plateau, of tweaks, adjustments & tests, 2 come 2 the conclusion that u hav reached ur natty limit. In other words, u don't just say, "I've reached my limit cuz I cant gain any mor", u mak adjustments in ur diet & training over an EXTENDED period of time 2 c if u can further ur gains.