"You know those sliding round discs where you put one foot there and you do your inner thighs, or you’re crossing behind? Anything to do with inner or outer thighs — that’s my struggle point, so I’m always trying to work on that part of my body," the 29-year-old told Health. "I love doing abs and I love doing arms, so legs are always the hardest for me. But they’re the most rewarding."
They’re generally called gliding discs, and they are small, round pieces of plastic that are placed under your hands and feet to increase resistance and add extra mobility to traditional exercises.
Basically, making them waaaay more challenging.
"With a normal lunge, you just bring your foot back and forward, with no resistance to the leg moving through the range other than air," kinesiologist and exercise physiologist, Dean Somerset, explained to SELF, "With a gliding disc [under your back foot], you maintain constant pressure down into the disc."
The mild instability the create also encourages your core to engage.
According to Valerie Waters, celeb trainer and designer of Valslides, by using the discs: “Every exercise becomes a core exercise, because those muscles are working to keep you upright.”
If you want to try these bad boys, keep you movements small at first so you can keep in control. As you improve, increase your range of motion, tempo and, if you’re game, add extra weights.