उत्तस्थुर्युगपद् वीरा: प्राणा मुख्यमिवागतम् ॥ २ ॥
uttasthur yugapad vīrāḥ
prāṇā mukhyam ivāgatam
When the Pāṇḍavas saw that Lord Mukunda had arrived, those heroic sons of Pṛthā all stood up at once, like the senses responding to the return of the life air.
The metaphor used here is quite poetic. When a person is unconscious, the senses do not function. But when consciousness returns to the body, all the senses spring to life at once and begin functioning. Similarly, the Pāṇḍavas all stood up at once, enlivened to receive their Lord, Śrī Kṛṣṇa.