glutton for punishment

a glutton for punishment (someone who seems to like working hard or eager to continue to do something difficult, unpleasant or unrewarding) {humorous (not derog.)} — человек, охотно берущийся за тяжелую или неприятную работу; работяга каких мало; настоящий работяга; работоголик в лучшем смысле этого слова; такому работу только давай; ему только подавай работу; сам не свой до всяких трудных заданий

Example 1: She works too hard. She is a glutton for punishment.

Example 2: I enjoy managing difficult projects, but I'm no glutton for punishment. Talk to someone else!

Example 3: Tina volunteered to organize our office party, she's a glutton for punishment.

"Hung in there seven or eight months. Every day. He was a real glutton for punishment. Pumping iron and doing aerobics plus martial arts. Ate his way through the pain. Man was getting tough enough to fuck a rock. Sorry. But he was. Then he quit. Two weeks after he won the bucks." (Dean Koontz, “Coldfire”)

Related vocabulary
[eager beaver]