In Pratikraman, lifting one knee (left or right) is a traditional kriyā used to express three things:

• Utthāna-bhāva (readiness to rise in respect): During portions like vandan/abbhutthio, raising a knee signals the inner intent “I rise to honor the Arihantas, Siddhas and Guru-paramparā,” while practically remaining in place.
• Alertness and modesty: It helps prevent pramāda (drowsiness/slouching) and keeps the posture attentive and respectful during long recitations.
• Practical comfort: It eases circulation and lets you smoothly move between kneeling, khaṁsaman, and kayotsarga without disturbing saṁyam.

Which knee to raise?

• The Āgamas do not mandate “left” or “right.” The side and exact moments are paramparā-based (local paddhati). Some follow right knee during certain vandans, others alternate, and some always use the same side. Digambar and Śvetāmbara traditions also differ in sitting styles and movements; follow your guru/upāśraya’s paddhati.

Key point

• The bhāva (inner repentance, reverence, and resolve) is primary. The knee movement is a humble aid to that bhāva, not an end in itself.

If you want a simple step-by-step outline of Pratikraman to see where such movements commonly occur, refer here: