backbreaking

形容词 backbreaking:

1. characterized by toilsome effort to the point of exhaustion; especially physical effort
   同义词：arduous, grueling, gruelling, hard, heavy, laborious, operose, punishing, toilsome

back.break.ing

adj.（形容词）
Demanding great exertion, especially physical exertion; arduous and exhausting.
艰苦的：要求很大的努力，特别是身体的费力；艰苦的和使人筋疲力尽的

【引伸】
back.break.er
n.（名词）