In line a the verb translated sustains means here “to help,” “to strengthen”; New English Bible “He nurses him”; Bible en français courant “takes care of him.”

In line b the Hebrew is “you will change all his bed in his sickness,” which means that Yahweh transforms the person’s illness into health, he restores him to health; New English Bible “he turns his bed when he is ill” is hard to understand. One possible version is “when illness befalls him you will make him well.” New Jerusalem Bible, with a marginal note that the meaning of the Hebrew is uncertain, translates “You will wholly transform his bed of suffering.” Instead of using the second person thou healest in line b, Good News Translation and others keep the third person used in line a.

Quoted with permission from Bratcher, Robert G. and Reyburn, William D. A Handbook on the Book of Psalms. (UBS Helps for Translators). New York: UBS, 1991. For this and other handbooks for translators see here .