If you’re looking for fitspo, look no further. Jessica Biel sees your leg day and raises you one muscle-shaking skater lunge workout.

The 37-year-old actress and fitness fanatic posted an intense move on her Instagram that’s equal parts entrancing and painful to watch. In the video, Biel is seen performing a super-slow set of weighted skater lunges while her trainer, Ben Bruno (who also trains Kate Upton and Chelsea Handler) slowly counts down the seconds.

The caption reads: “Never has anyone in the history of the world counted slower than my trainer @benbrunotraining.” Anyone who’s ever done a guided workout knows how time seems to slows to a stop when performing particularly excruciating exercises, but of course, Biel powers through the move like an absolute champion.

 

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Never has anyone In the history of the world counted slower than my trainer @benbrunotraining (🔗👆🏻) #ad

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Even more impressive is Bruno’s post on his own Instagram, where he shares that she performs three sets of the six reps shown in the video. “Wanna see something crazy? @jessicabiel does skater squats with 8 second eccentrics for sets of 6 reps. This is just nuts. This isn’t something we did one time for the video either; this was her third set and I have her do these routinely,” he wrote, adding. “It’s really a wonder she hasn’t fired me yet.”

And there you have it! The secret to Biel’s famous booty is the single-leg skater squat, a challenging move that not only works your glutes but a number of other muscles, too. “By focusing on one side of the body, you’re able to improve balance, build stability, and override muscular compensation in the glutes and quads while getting an amazing calorie torch,” Chicago-based celebrity personal trainer Gideon Akande told Well+Good.

 

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Hey, Emmy, my butt is coming for you. (Assuming I can walk after these pistol squats) 😬

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Biel is no stranger to the workout game; she frequently posts her intense workouts on social media, and last year, co-designed a capsule collection of stylish yet simple athleisure staples for Gaiam. Clearly, all of the challenging moves have paid off.

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