The works of Ādi Śaṅkarācārya

Bṛhadāraṇyakopaniṣadbhāṣyam

Verse 235

तद्यथानः सुसमाहितमुत्सर्जद्यायादे- वमेवायश् शारीर आत्मा प्राज्ञेनात्मना- न्वारूढ उत्सर्जन्याति यत्रैतदूर्ध्वोच्छ्वासी भवति ॥ ३५ ॥

In plain words

Think of a heavily loaded cart, creaking as it moves. That is exactly how it is: the embodied self, carried along by the deeper self that is pure awareness, goes forward groaning — in that hour when the breath turns upward.

Close to the Sanskrit

As a well-loaded cart would go creaking, so this embodied self, mounted by the self that is prājña, goes forth groaning, at the time when it becomes one whose breath goes upward.