Adam Clarke on Psalms 129:3

The plowers plowed upon my back - It is possible that this mode of expression may signify that the people, during their captivity, were cruelly used by scourging, etc.; or it may be a sort of proverbial mode of expression for the most cruel usage. There really appears here to be a reference to a yoke, as if they had actually been yoked to the plouph, or to some kind of carriages, and been obliged to draw like beasts of burden. In this way St. Jerome understood the passage; and this has the more likelihood, as in the next verse God is represented as cutting them off from these draughts.