Also often used with a possessive and immediately followed by an infinitive
You better be busting your ass if you want to finish the job on schedule.
I was busting my ass to finish my homework on time.
also see busting ass
past tense: busted ass
"Damn, it sounds like a grizzly bear growling in here! No, it was just dad busting ass again"
"My ol' man busted ass so hard it woke me up!"
i needed to bust ass so bad while I was waiting in line at the bank, but instead I waited until I was outside and finally let one rip.