adjective

extremely tiring and demanding.

a gruelling schedule

exhausting,tiring,fatiguing,wearying,enervating,taxing,draining,sapping,debilitating,demanding,exacting,trying,difficult,hard,arduous,laborious,back-breaking,strenuous,harsh,severe,stiff,punishing,crushing,crippling,grinding,brutal,relentless,unsparing,killing,murderous,hellish,knackering,exigent