godan verb (-ru), intransitive verb
work hard; take pains; exert oneself
Used when someone puts in considerable effort or goes to trouble, often for the sake of others or a task. Can carry a nuance of self-sacrifice or going out of one's way.
彼は家族のために骨折って働いている。
He works hard for his family.
この企画を成功させるために骨折った。
I took pains to make this project a success.