From Longman Dictionary of Contemporary Englishbackbreakingback‧break‧ing /ˈbækbreɪkɪŋ/ adjective DIFFICULTbackbreaking work is physically difficult and makes you very tired► see thesaurus at tiring
Examples from the Corpus
backbreaking• Now, after thirty days at this backbreaking and endless task, he realised why.• Training for the University boat race must be one of the most backbreaking, brain blowing experiences in sport. 