© Matt Winkelmeyer/Staff/Getty Images for dcp Hint: You don’t necessarily need to be at a gym to use this equipment.

Hailey Bieber may know how to look stylish during a workout, but her fitness accessories include more than just cute pairs of leggings.

She recently hit the gym with her stylist Maeve Reilly, who shared clips of their sweat sesh on her Instagram Stories.

Under the guidance of Dogpound trainer Kevin Mejia, Bieber and Reilly performed a series of donkey kicks—but ICYMI, the duo’s lower-body workout included a piece of workout equipment you might never have considered using: ankle weights.

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Donkey kicks (named after the way donkeys kick their hind legs, FYI) are powerful compound exercises that help you target more than just the muscles in your legs and glutes, says Rocky Snyder, C.S.C.S., a Santa Cruz-based strength coach.

“Most Americans spend way too much time sitting in a hip-flexed position,” he explains. “Donkey kicks encourage just the opposite action (an extension of the hips) to occur. By performing the donkey kicks on the hands and one knee, it also encourages more involvement of the muscles between the ribs and hips,” meaning it can work both your core and your butt. (Related: 5 Ways to Build Bigger, Stronger Glutes That Have Nothing to Do with Squats)

As with any exercise, proper form is crucial, explains Snyder. You’ll want to keep your spine—especially the lower back—from dipping down as the leg raises, he says. “The goal is to extend at the hip joint, not at the spine,” he adds. “If the spine moves more, then it becomes a lower-back exercise, not a butt exercise.”

But exercises like donkey kicks can easily be taken to the next level by adding ankle weights into the mix. Not only are they versatile and easy to take on-the-go, but ankle weights also allow you to maintain a good range of motion and rotation compared to traditional weight equipment, which is especially beneficial for exercises involving the hips, Holly Perkins, C.S.C.S., author of Lift to Get Lean, previously told us. “The hip is a ‘ball joint’ that moves in all directions,” Perkins explained. “It’s important to strengthen the numerous movement patterns and large and small muscles that are at play.”

While Bieber’s stylist wore her weights around her ankles, Bieber’s were secured just above her knees. “The major difference between having the weight at the ankle instead of near the hip is how much the calf and hamstring muscles are involved,” explains Snyder. “The closer the weight is toward the ankle, the more likely the calf and hamstring muscles will help out. This will reduce the intensity of gluteal work. The closer the weight is toward the back of the knee, the more likely the glutes will be isolated.”

Translation: If you want your donkey kicks to really work your glutes, strap on a pair of ankle weights and slide those bad boys up toward your knees. (Related: The Butt Workout with Weights That’ll Sculpt Your Best Butt Ever)

It’s not clear what type of ankle weights Bieber was using in her workout, but if you’re simply looking for a solid pair to get you started, Snyder recommends Valeo Adjustable Ankle/Wrist Weights (Buy It, $18-$30, amazon.com), which come in pairs of 5-, 10-, or 20-pound weights. They’re also adjustable, so you can vary the amount of weight used for increased or decreased resistance, depending on the particular exercise or your own abilities.

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Looking for other exercises you can do with ankle weights? No problem: Snyder says they’re such a versatile type of gym gear, they can really be used with almost any strengthening exercise. “If we consider the underlying purpose of ankle weights (to add a higher level of resistance than normal bodyweight can provide), then they can potentially be incorporated into any movement in a person’s workout routine,” he explains. Here are a few ideas to get you started:

Downward Dog with Leg Raise

Snyder recommends wearing ankle weights while doing this traditional yoga pose, which involves starting in a downward dog position, then “lifting one leg [at a time] high off the floor above the hip.” However, it’s important to make sure you’ve mastered the correct form of this movement before adding the ankle weights, adds Snyder. “It’s essential that you have the strength and control of your own bodyweight in any exercise before you begin to add external loads,” he advises. (Related: How to Transition Between Yoga Poses with Grace)

Curtsy Lunge

For this hip-strengthening curtsy lunge variation, you’ll want to wear an ankle weight around one ankle and the other weight around your wrist on the same side, explains Snyder. “With the loaded leg, reach back behind the body as far back as possible while taking the same-side arm up overhead as high as possible.”

Plank Reach

Start in plank position, says Snyder. “Take the ankle weight in one hand and place it as far as you can reach (safely) away from the body [in any direction]. Then use the opposite hand to bring the ankle weight back from that spot and place it in a completely different location almost out of reach. This move will really challenge your coordination while strengthening your upper and lower body at the same time.”

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