限界(げんかい)limit, bound

体力(たいりょく)の限界(げんかい)を感(かん)じる。

To feel the limits of one's physical strength.

それが彼女(かのじょ)の能力(のうりょく)の限界(げんかい)だと思(おも)います。

I think that is the limit of her ability.

一人(ひとり)の力(ちから)には限界(げんかい)があるので助(たす)けてくれませんか？

Because there's a limit to how much one person can do, would you help me?

もう一歩(いっぽ)も歩(ある)けないほど、体(からだ)の疲(つか)れが限界(げんかい)に達(たっ)した模様(もよう)だ。

His body seems to have reached the limit of its fatigue to the point where he cannot take another step.

散々(さんざん)生徒(せいと)たちには優(やさ)しく指導(しどう)してきたが、これ以上(いじょう)はもう我慢(がまん)の限界(げんかい)です。

I have been patiently and kindly guiding the students for a while, but now I've reached my limit, and I can't put up with it anymore.