It's called an eccentric functional trainer, and you're going to want to try out this unique piece of gym equipment, stat.

By Faith Brar
February 20, 2019
Photo: Gary Gershoff / WireImage / Getty Images

Ashley Graham is known for sharing badass videos of herself training-and girl does not take it easy. Case in point: This time she did what are essentially medicine ball suicides for cardio or this brutal mini-band butt finisher at the end of her workout. (Both of which had us sore just watching-but here's even more proof Ashley Graham is insanely fit.)

Recently, the Sports Illustrated swimsuit model shared Instagram story videos of her using what's called an eccentric functional training machine-and it had us shook.

Confused? You're not the only one: This isn't a piece of equipment you see in just any gym. Basically, you stand on a base and lower into a squat, then attempt to hold that position while the base begins to move forward, up, back, and down, in circles (kind of like a surfboard on waves).

Photo: Instagram Stories

Like all things, Graham makes the movement look like a walk in the park-but it's far from it. "It's hard as hell," says Pamela Geisel, M.S., C.S.C.S., certified trainer and exercise physiologist. "This machine is great in building strength eccentrically, which we don't do often."

If you frequent the gym, there's a pretty good chance you've heard the term "eccentric exercise" tossed around. While it may sound fancy, it's a simple concept: These exercises focus on working muscles as they lengthen, as opposed to when they contract. There's an eccentric part to every exercise; for example, in a biceps curl, it's happening when you're lowering the dumbbell back down to the bottom of the rep and resisting the weight of the dumbbell on the way down.

How is that beneficial, you might ask? "Eccentric movement helps us control slowing our body weight," says Geisel. "So think about changing direction in a tennis game or descending stairs. When we lack the strength to control that movement, the joints above and below take a hit." (Bonus: Eccentric moves are also more likely to leave you really sore.)

The machine works your entire body but is also specifically great for your abs. "She's working all of her core stabilizers and balance," says Geisel. "My guess is she does this for short periods of time because the working muscles are constantly under tension." (Related: I Worked Out Like Ashley Graham and Here's What Happened)

If you're dying to fit some eccentric movements into your workout routine, but don't have access to this fancy piece of equipment, take a cue from this essential weekly gym workout plan. Not only is it a great way to ease into strength training, but it also offers some eccentric exercises to challenge your muscles in new ways.