Riverdale may have just wrapped filming, but actor Madelaine Petsch (aka Cheryl Blossom) is still putting in work at the gym. This week, Petsch shared an Instagram Story of herself doing a workout with her trainer, Mack, who also works with celebrities like Ariel Winter and Jordyn Woods.

In the video, Petsch is working her glutes with a resistance band. The move is so tough that she captioned her photo, "Definitely won't be able to walk tomorrow."

You can check out what the move looks like here:

Instagram / @madelame

This leg-lift exercise targets your butt, but also works your upper body and core.

"We call this move a table-top glute exercise," Elisabeth Halfpapp, executive vice president and barre and yoga teacher trainer at exhale, where she co-founded the Core Fusion barre program, tells SELF. Holding the all-fours position works the upper body and core, while the leg lift with a resistance band targets the gluteus maximus, the largest muscle in the butt. Since one leg is lifted throughout (yes, you'll have to do this exercise on each side), it also challenges your balance.

To set up for this move, start on all fours, and slip a resistance band—either one with handles, like Petsch's, or one that's just a loop—around your ankles. Then, make sure your body is aligned properly, with your elbows slightly bent, shoulders directly over wrists, hips directly over knees, and head lifted in line with your spine to keep from straining your neck. Keeping your hips level and your core stable, extend one leg straight out behind you. Then, lift the leg straight up until you feel a contraction in your butt.

Instead of lowering the leg all the way down to the mat, simply lower it down an inch, and then lift up an inch, says Halfpapp. That's 1 rep. Start with 15 to 20 reps on each side, then repeat on the other leg.

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Start by trying the move without the resistance band, and then add it when you're ready to increase the intensity.

If you're a beginner, you can skip the band entirely. "[You] can perform the same exercise without the resistance band and with [a smaller] range of motion," Jaime McFaden, NASM-certified personal trainer and Aaptiv trainer, tells SELF. If this all-fours position feels uncomfortable on your knee, fold a mat a few times and place it underneath the standing knee for extra cushion. If you have knee issues, talk with your doctor or physical therapist before doing this or any other move that puts weight on your knees. If you have ankle issues, ditch the resistance band, McFaden says.

When you feel ready for an extra challenge, try adding the band. "It increases the intensity of the exercise, so you'll feel the burn in your muscles with fewer reps," says Halfpapp. Increasing the intensity also means you'll be able to challenge your strength and stability more than you would with just your bodyweight.

If you've ever taken a barre class, you may have done a similar move but with your knee bent and holding a dumbbell. While that's also a great variation of this exercise and works the butt in a similar way, using a band gives you more control over the resistance, since it's working off your bodyweight versus an external load, McFaden says.

McFaden suggests working Petsch's move into a longer butt workout.

A sample circuit could include "straight leg kick-backs, followed by bent-leg kick backs, fire hydrants,, and side-lying leg raises," she says. Here are some more great options for resistance band butt exercises. Pick four or so, and try 15 to 20 reps of each—just be prepared, like Petsch, to feel the burn.

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