When J.Lo gives us a peek into her workout routine, we pay attention. The famously fit star (can you believe she's 48?) always looks incredible, whether she's slaying the red carpet or fighting corruption as police officer Harlee Santos in her show Shades of Blue.

Although genetics surely play a role in Lopez's insanely toned physique, it's no secret that she's seriously dedicated to her fitness—the A-lister often works out with Tracy Anderson and has even been spotted hitting the gym with The Rock. Yesterday, we got a glimpse into how Lopez gets her super-toned arms when she shared her upper-body workout with followers in a video on Instagram.

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In the snaps (which she captioned "Gettin' it in!!"), Lopez proves she's a resistance band master by demonstrating a series of intense bicep curls. Celebrity trainer David Kirsch, who works with Lopez, tells Health that the move is called the bent over resistance row with curl. "I love to keep workouts with Jennifer high energy and high intensity, making sure the full-body workouts are fresh and always changing," he says.

If you often use free weights on arm day, resistance bands are a great way to change things up; by forcing you to literally resist your own body weight, these stretchy plastic bands will take any workout to the next level.

"I like using resistance bands because these workouts are something my clients can easily do with no time at the gym, and they are so transportable," Kirsch says. 

In addition to strengthening the upper body, Kirsch tells us that this move also helps tighten and tone the quads, glutes, and core. The tool J.Lo is using is mounted to a wall, but you can modify the move with a loose resistance band by stepping on it in the center and pulling the ends towards your chest.