形容詞 backbreaking:

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

back.break.ing

adj.（形容詞）
Demanding great exertion, especially physical exertion; arduous and exhausting.
艱苦的：要求很大的努力，特別是身體的費力；艱苦的和使人筋疲力盡的

【引伸】
back.break.er
n.（名詞）