Meaning: do very difficult physical work and makes you very tired.
کار کمر شکن، کار کشنده، کار شاق
Example: cleaning all the floors was backbreaking work.
تمیز کردن کف تمام اطاق ها کار کمر شکنی بود
Example: digging the garden was backbreaking work.
Example: he is demanding a backbreaking work from me.