Green’s Dictionary of Slang

1. exhausting, tiring.

1973		R. Roth Sand in the Wind 42: And we had these ass-busting working parties every fucking day.
1979		J. Hurling Boomers 31: A day of heads-down, ass-busting work.
1990		Cincinnati Enquirer 🌐 It is ass busting work. I routinely take breaks and pretend to take notes so I can rest.
1999		Salon.com 4 May 🌐 The crushing economic realities and the graceless development of the American West are forever encroaching, making work as a modern-day cowboy a monotonous, ass-busting job.

2. remarkable, amazing.

2001

USA Today.com 15 Feb. 🌐 Have you ever thought of coming to Moscow and St. Petersburg, Russia and putting an ass busting performance in front of Russian audience?