Modifies a noun

• job: It was a backbreaking, frustrating job to keep them running, especially the night sleeping car trains.

• work: Take the backbreaking work out of weeding with this handy little weed wand.

• labor: The invention of gears and pulleys made light of much backbreaking labor, it was also used in the torture chamber to break backs.

• effort: It is ideal for the keen gardener who prefers not to put backbreaking effort into the job.

• hour: One person who won't be watching: Laila, who is going to be either working backbreaking hours or snatching some sleep.

• task: Moving into loading and firing positions by muscle alone, each gun had a crew of several men to perform these backbreaking tasks.