'Knees' in the Bible

Then the king’s face grew pale, and his thoughts alarmed him; the joints and muscles of his hips and back weakened and his knees began knocking together.

Now when Daniel knew that the document was signed, he went into his house (now in his roof chamber his windows were open toward Jerusalem); he continued to get down on his knees three times a day, praying and giving thanks before his God, as he had been doing previously.

Then behold, a hand touched me and set me unsteadily on my hands and knees.