Adidas Adizero Prime X Strung Review: This Rule Breaker Is Fantastically Bouncy

Were it not for World Athletics setting a stack height limit of 40mm for races, many of the best carbon plate running shoes might now look like the Adidas Adizero Prime X Strung, which has a stack height of 49.5mm.

All that foam, plus other tech in the midsole, produces a powerfully propulsive and enjoyable ride for long races, though trade-offs come in the extra weight and instability the high stack creates. I wouldn’t race in it, but if you have no qualms about that stack height then the Prime X Strung is a top option for marathon racing—as long as you escape the heel rub I experienced.

Adidas Adizero Prime X Strung Review: Price And Availability

The Adidas Adizero Prime X Strung launched in September 2022 and costs $300 in the US and £230 in the UK. The US price is outlandish, even for carbon super-shoes; significantly more expensive than the Nike Alphafly NEXT% 2 and Saucony Endorphin Elite. In the UK, the price of the Prime X Strung is par for the course with carbon shoes. Adidas’s legal racer—the Adidas Adizero Adios Pro 3—costs $250/£220.

Design And Fit

The main update to the Prime X Strung, compared with the original Prime X, is a one-piece upper. This uses the brand’s Strung technology, which allows yarns individually to add support around the heel and midfoot. It looks great and is an improvement in the toe box compared with Adidas’s other racing shoes. I had to go a half size up in the Pro 3 to get the correct fit around my toes, whereas I am true to size in the Prime X Strung.

However, the fit around the heel has been terrible for me. There are two strips of cushioning on either side at the back, but this doesn’t create a secure hold and I have had the worst heel rub I’ve experienced in any shoe while testing the Prime X Strung. Even when I heel-locked the shoe it didn’t solve the issue. I didn’t have this problem with the Adios Pro 3, which has a similar design at the heel but fits more securely.

The midsole of the Prime X Strung is made from Adidas’s Lightstrike Pro foam, which is as bouncy as you’d expect on a super-shoe. It also has a small plate under the heel, plus Adidas’s carbon EnergyRods under the forefoot, which deliver the same kind of propulsion as a full plate while being more flexible.

Underneath the EnergyRods are three TPU plastic EnergyBlades to add even more pop to your forefoot. The Adios Pro 3 doesn’t have these, and it also has a stack height of 39.5mm at the heel, which is 10mm lower than the 49.5mm stack height on the Prime X Strung. The stack height is 41mm at the forefoot, for an 8.5mm drop.

At 9.4oz/266g in my UK 9, the Prime X Strung is the heaviest bona fide super-shoe I’ve tested, which you’d expect given the higher stack. It’s around 20g heavier than the Adios Pro 3 (in a size 9.5) and Nike Alphafly NEXT% 2.

The outsole uses Continental rubber to cover the forefoot, with two strips of rubber at the heel. I’ve found that the shoe grips well for me in wet conditions, which helps with cornering in such a tall shoe.

How I Tested This Shoe

I have used the Prime X Strung for a track session running one-mile and 200m reps, plus a couple of progression runs on the road, including a tough 10K in 35 minutes. I didn’t test the original Prime X, but have tested every generation of the Adios Pro, along with most of the best carbon plate running shoes on the market.

Running Performance

The Prime X Strung is every bit as bouncy as you’d expect from looking at it. It’s remarkably propulsive, and that spring only becomes more noticeable the faster you run in it.

It’s a shoe that makes moving fast feel effortless, and it protects your legs during a session more than any other shoe I’ve come across. The day after a hard track session running a couple of mile reps sandwiching two sets of 8 x 200m, my legs were so fresh that I barely felt like I’d run at all. 

As a result of the huge stack you don’t have much feel for the ground when using the shoe, and I felt like I had to keep my eyes glued to the sidewalk at all times to avoid even the slightest pothole, because hitting uneven surfaces in the shoe is a recipe for a rolled ankle. The heel is quite narrow for such a high stack, which adds to the instability at slower paces and when cornering. That said, when running fast in the shoe I didn’t feel like the wobbliness negatively affected my running—or at least the trade-off was worth it for the springiness underfoot.

My hardest run was a progression 10K moving from 3min 45sec/km to 3min 18sec/km. It’s a run I do semi-regularly during training and the Prime X Strung was fantastic for it, getting bouncier and bouncier as I moved through the gears. It did feel a bit big and hefty when I kicked for home in the final kilometer, but overall it was as good as any carbon shoe I’ve tested during this type of run.

But it’s not a shoe I’d be able to use much, mainly because of the heel rub I experienced. Also, the instability may well prove a problem for many people running on uneven sidewalks. Unless you’re on a flawless surface, you have to keep your wits about you when running in the Prime X Strung.

Is The Adidas Adizero Prime X Strung Worth It?

Looking purely at performance, the Prime X Strung is one of the best marathon running shoes. It’s a little awkward and heavy for races shorter than half marathons, but the bounce it delivers is perfect for longer events. As you might expect from the design, it feels like a souped-up Adios Pro 3.

However, I don’t think it outperforms my favorite long-distance marathon racing shoes, like the Nike Alphafly NEXT% 2 or Mizuno Wave Rebellion Pro, which have the bonus of being permitted under World Athletics’ rules. The Alphafly is also more stable, and I’ve found it forgiving of sloppy form when tired in the late stages of a marathon.

If you’re not an elite runner then in theory you don’t have to worry about the rules, but as a reasonably fast amateur it wouldn’t even occur to me to use the Prime X Strung instead of a race-legal shoe, and I’ve never seen it on the feet of runners around me at races. Given that I think there are legitimate shoes that are just as good for the marathon, and nimbler faster options for shorter events, I wouldn’t splash the cash on the Prime X Strung.

It’s also a shoe I wouldn’t regularly use in training, mainly because of the heel rub. If that doesn’t affect you and you have even roads to run on, then it is a great training option for speed sessions. It’s expensive to buy purely for training though, so it would probably only be worth buying if you were also happy to race in it despite the high stack.