backbreaking (adj.)

• annoying
• arduous
• bothersome
• burdensome
• crushing
• effortful
• forced
• grueling
• hard-fought
• heavy
• hefty
• irksome
• killing
• labored
• laborious
• onerous
• operose
• oppressive
• painful
• plaguey
• punishing
• strained
• strenuous
• toilsome
• tough
• troublesome
• trying
• uphill
• vexatious
• wearisome