BACKBREAKING
arduous, backbreaking, grueling, gruelling, hard, heavy, laborious, operose, punishing, toilsome
(adjective) characterized by effort to the point of exhaustion; especially physical effort; “worked their arduous way up the mining valley”; “a grueling campaign”; “hard labor”; “heavy work”; “heavy going”; “spent many laborious hours on the project”; “set a punishing pace”
Source: WordNet® 3.1
Etymology
Adjective
backbreaking (comparative more backbreaking, superlative most backbreaking)
(figuratively) Of work, very physically tiring.
Source: Wiktionary