The hardest jumping jack you will ever do involves a resistance band and *all* of your muscles

I never, ever thought that jumping jacks—of all the fitness moves that exist—would be the hardest thing I’d ever do in a workout. Usually, they’re the innocent cardio burst you turn to mid-sweat sesh, or the thing you do as an active recovery… but this morning, I did a form of jumping jacks that fired up my body from head to toe and left me barely able to walk afterwards.

Let me explain: I woke up early this AM to workout with celebrity trainer Don-A-Matrix, AKA the guy you’ve definitely seen on Keeping Up with the Kardashians making Kourtney, Kim, and Khloe sweat. I thought I knew what I was in for… but things quickly got revved up and my body somehow made it through a scorcher of a 45-minute workout.

Said jumping jacks were not your everyday, hands clap over head, feet jump outwards kinda move. These suckers involved a resistance band with handles. You step your feet onto the band itself in the center on the floor, and take the handles with your hands. Then you jump into “jack,” by pushing your hands upwards and your legs outwards. It’s no joke.

“Jumping jacks are a great way to activate several muscle groups when working out, and they’re perfect to use for warm-ups or in any sort of high-intensity workout,” says Don, who’s also trained professional athletes and works with premium sports drink BODYARMOR (his go-to which is full of coconut water and electrolytes, BTW). “They work most of the muscles in your arms and legs, all while strengthening your heart.”

He decided to make them kick even more ass with the use of a resistance band, which adds a level of increased versatility and works several muscle groups in one fell swoop. And that’s how his entire Matrix workout—an intense training method that involves the hard-hitting combo of resistance bands and cardio, together—came to be. “When most people go to the gym, they do resistance band-strength training and cardio separately,” says Don. “With that in mind, I wanted to come up with a workout that delivered results by incorporating both types of exercises to tone and sculpt the body.”

Doing a cardio/resistance hybrid feels twice as hard as doing resistance band work on its own, because you’re working more muscle groups at once, he explains. “It’s taxing on the body to do both cardio and resistance-band strength training at once,” says Don, who thankfully divides his class into quarters with a hydration break between each one. No kidding. If you ever want to make basic moves a zillion times harder, add a resistance band and get to it. (I’m still sore, BTW.)

For more sweat sesh ideas, here’s an at-home HIIT workout you can do from your living room. And a 6-minute abs workout to round it all out.