The singer threw some punches for her first workout after her kidney transplant.

By Julie Mazziotta
October 02, 2017

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 is back in fighting shape!

The singer threw more than few punches at  in New York City on Thursday for her first workout , and according Rumble co-founder and co-owner Noah D. Neiman, “she killed it.”

“She just came in and went hard. We were all, ‘Okay, that’s what I’m talking about!’ ” Neiman tells PEOPLE of Gomez, who took his colleague Joe Ferraro’s class.

But Gomez, 25, told them that she can go even harder.

“She said, ‘No guys, I’ll bring my A game next time’ and I was like, ‘What?! Look at you, you just had surgery,'” Neiman says. “She legit has a whole new kidney! But she was great.”

Gomez revealed on Sept. 14 that she had undergone a kidney transplant as part of , and her donor was her best friend, . A source close to Gomez  that the popstar is feeling better than she has in months.

Selena Gomez Says Her Kidney Transplant Donor Was Her Best Friend, Actress Francia Raisa

“She’s really bounced back more quickly than everyone expected,” the source said of Gomez, who hit the gym in a Maje x Schott coat in between  in New York City.

, 29, is also hitting the gym after the transplant, that she’s “happy to be back” as she lifted weights.

Rumble, which is known for their group fitness classes featuring 10 rounds of boxing and strength training, is a favorite of many celebs. ,,  and  have all been spotted at the gym when they’re in the Big Apple.

  • Reporting by JANINE RUBENSTEIN