Matthew Poole and continuators on Psalms 129:3

3 The plowers plowed upon my back : they made long their furrows .

They have not onely thrown me down and trod me under foot, but have cruelly tormented me, wounded and mangled me, and had no more pity upon me than the plowman hath upon the earth which he cuts up at his pleasure. He saith, upon my back, either because they did literally scourge the Captives upon their backs with such cords as are mentioned v. 4. although we do not read that the Israelitish Captives were thus used by any of their enemies; or by way of allusion to that usage, which made a sort of furrows in their backs upon which they used to lay on their strokes.

They oft repeated their injuries and prolonged my torments.