The comedian posted an Instagram video of himself boxing with a punching bag during the ceremony, with ABC playing on a TV conspicuously in the background.
"When you feel like u have nothing left is when you find a way to push & give more....Always grinding. #HustleHart," he wrote.
Hart, 39, was named host of the 2019 Oscars before he faced severe backlash over past tweets and comedy bits that some felt were homophobic in nature.
In December, he tweeted that he was stepping down as host of film's biggest night.
"I have made the choice to step down from hosting this year's Oscar's [sic] ....this is because I do not want to be a distraction on a night that should be celebrated by so many amazing talented artists," he wrote. "I sincerely apologize to the LGBTQ community for my insensitive words from my past."
He added, "I'm sorry that I hurt people.. I am evolving and want to continue to do so. My goal is to bring people together not tear us apart. Much love & appreciation to the Academy. I hope we can meet again."
Ellen DeGeneres lobbied for Hart to be reinstated as host of the Oscars, after which the "Night School" star reportedly spent time "evaluating" a return to the Oscars stage, but ultimately decided against it.
The Oscars went on without a host.