他发现自己已无力应对那份劳神费力的工作了。He found he could no longer cope with his demanding job.他派我去干白费力的事。He sent me on a fool's errand .这项费力的工作足以使人精疲力竭.This exhausting work is enough to run everyone down....

“费力的”的英语可以翻译为：arduous，operose，taxing，toilsome，exertive ...