backbreaking

Etymology

back + breaking

adj

1. (figurative) Of work, very physically tiring.
   A few keen enginemen, such as Driver Rosewarne of York, could coax good work out of them when engaged in heavy East Coast express service, but to most footplate crews, especially firemen, they were rather heartbreaking and backbreaking machines, and gradually were relegated to secondary or fast goods duties. 1949 May and June, R. A. H. Weight, “A Short-Lived Pacific Class”, in Railway Magazine, page 196
   Ahead … each woman is stooped beneath a backbreaking load of firewood. 2019, Maaza Mengiste, The Shadow King, Canongate Books (2020), page 110