on one's last legs

Prepositional phrase

idiomatic broadly

(idiomatic) About to die. / (idiomatic, by extension) About to lose viability or become defunct.

Japanese Meaning

もうすぐ死にかけている状態 / 存続や機能が著しく低下し、間もなく使えなくなる状態

After months of nonstop travel, being on one's last legs is understandable.

何か月も休みなく旅した後で、瀕死の状態になるのは理解できる。

Sense（1）

(idiomatic) About to die.

Sense（2）

(idiomatic, by extension) About to lose viability or become defunct.

[T]he wood was main dark, but had a kind of a low glow in it like a fire on its last legs.