Tennis player Ajla Tomljanovic used to hate training in a weighted vest. They were bulky and uncomfortable, and though they added a weight challenge, they impeded her from actually practicing her tennis moves.

But today, she partially attributes training in a sleek new weighted vest from the Nike exec-founded company Omorpho with helping to give her the edge she needed to achieve the feat she’s become best known for: beating Serena Williams in the final match of her career at the U.S. Open.

The new Omorpho G-vest+ launched on Monday at an event in West Hollywood which featured Tomljanovic and other athletes on a panel, where they shared their experience with it. The G-vest+ was specifically designed for women (though there is also a men’s style). It has a zip-up front, adjustable shoulder straps, and bungees on the sides so you can ensure it fits snugly and cinches at the waist. It also comes with a companion app that gives you workouts to do in the vest—with the app open, you just tap your phone to the vest and your workout will surface.

If you haven’t seen Omorpho gear, they are the weighted activewear company that actually makes adding extra pounds to your bottoms and tops look cool. They distribute the weight across the clothing in small beads covered with fabric in a design they call “microloading.” Wearing the gear, you sort of look like a dragon. The women’s vest microloads five pounds of weight, while the men’s adds 10 pounds.

That means when you squat, lunge, push up, or just walk around the block, you’re adding a strength training element to your workout. For athletes, that’s important because once they take off the gear, they’re able to run faster, or hit harder, since they’re no longer wearing the added weight. But for people just looking to get some exercise, it’s a hell of a way to turn up the heat on your workout.

I got to try a 20-minute HIIT class wearing the Omorpho vest. That may sound like a pretty short workout. But wearing the vest, my legs were fully gassed by the end.

I worked with an Omorpho rep to make sure the vest was fitted just right. As a curvy 5-foot-1 woman, I wore a size large to make room for my chest, while we shortened the shoulder straps and tightened the waist to fit it to the rest of my smaller frame. I noticed that my vest went down closer to my lower back, while on taller folks it came to around their waist. But that didn’t make it uncomfortable. My only complaint was that my chest was a bit smushed (even after sizing up), and that I had to make a more conscious effort to stand up straight.

The workout began with some jumping jacks, and right away, I felt a difference. But wearing a weighted vest plays tricks with your mind. You notice the added challenge, but since you’re not actually holding anything (like dumbbells), you move your body with the same vigor you would with just bodyweight. That means you’re doing the same exercise, with more impact.

This dynamic has its pros and cons. It definitely resulted in an intense workout. You don’t usually hold weights while jumping, so the vest added a new dimension to plyometric moves like burpees and jump squats. By the end of my third set of plyometric split squats, I could barely lunge down anymore, and my quads, glutes, and hamstrings were quaking. Push-ups and planks also brought the sweat dripping.

When I’m holding something like hand weights or a medicine ball, I usually go slower than I would with a bodyweight move, taking care to maintain good form. I tend to sway my lower back if I don’t keep my abs tight during strength training. But adding a weighted vest to a HIIT class—even when it’s just five pounds—kind of makes you lose sight of that necessity, and I found I ended up sacrificing form for speed. After that 20-minute class, I felt a twinge in my lower back that bothered me. That’s on me for not using good form, but it’s also because I was less conscious of doing so because the weight was attached to my torso, not something I was holding.

The Omorpho G-Vest+ added a challenge that was satisfying and efficient. With more practice, I think I would adjust to carrying the load so that it wouldn’t affect my form. Since it’s only five to 10 pounds, it’s not a replacement for strength training. But it’s a fun way to make bodyweight training or cardio extra challenging on days when you’re feeling up for it. And you’ll look pretty cool, too.

Whether you’re adding weight or not, try this HIIT workout to bring the heat.