Matthew Poole and continuators on Exodus 17:12

12 But Moses hands were heavy, and they took a stone, and put it under him, and he sat thereon: and Aaron and Hur stayed up his hands , the one on the one side, and the other on the other side, and his hands were steady untill the going down of the Sun.

Not that both hands were erected and joyned together, which was not a fit posture for one holding a rod in his hand, but that Moses shifted the rod out of one hand into the other when the former was weary, and that Aaron and Hur did each of them with both hands hold up that hand which was next to them successively, that they also might relieve one the other.