Jennifer Aniston’s trainer says you’re missing out on this one thing that gives you a better workout

Last night, I worked out with Jennifer Aniston‘s boxing trainer. And after decades of thinking that I knew exactly what I was doing, I learned something game-changing about how you should be starting your sweat sesh. Yes, it’s great to get into a gym and jump right into your workout, but chances are your regimen could benefit from adding one essential step before you hit the weights: mobility training.

“The foundation of working out is moving better, so you want to mobilize the body before you start any workout,” says Leyon Azubuike, boxing pro and founder of Gloveworx, an LA-based studio that just opened its first New York City location. Mobilizing your body before you move is sort of like a mix between a warmup and stretching, but it’s more focused on opening up your body, which is protracted after being hunched over at a desk all day.

Azubuike likens your body to a car: “After typing all day and all of a sudden going to your workout, you just want to drive your car,” he says. “But the engine is cold in the car—it’s like going right from the room to driving 60 miles per hour. That’s not gonna work. You’ve got to warm the car up and then go.” So, without mobilization exercises, your workout is like igniting your body straight to fourth gear—and that leaves you more prone to injury.

What exactly are mobilization exercises, you may ask? Good question. They consist of a lot of muscle activations that prep your body for movement and take your joints through their full ranges of motion. Azubuike had me doing inchworms, T-spine rotations, cat-cows, and squats and lateral walking with bands around my ankles and above my knees (which burned my bum). “I love things that are in the quadruped position,” he says. “Groin stretches are good, stabilizing activations—keep your knees bent, core tight, and the chest up, and practice turning off the traps and turning on the scaps. This way you’re fighting against the polar lean and standing tall and upright.”

It’s particularly key to “turn off the traps and turn on the scaps,” as Azubuike says, since your trapezius muscle (an upper muscle that moves your head) gets hunched during the workday and your scapular muscles—which handle your posture—need to open up. Pushing your arm muscles in outer directions help with this.

After about 10 minutes of mobility exercises, Azubuike took me through an interval on a VersaClimber (killer) followed by an intense boxing sesh and then a flowing plank sequence. And I was beat and completely dripping with sweat. But you know what? My body did feel more open and ready to take on all of that intensity. Consider me a new mobility exercise devotee.

If you’re into punching bags, check out these boxing move tips. And you can copy Gigi Hadid’s boxing workout straight from her trainer Rob Piela.