With a stack height of 50mm in the heel, the Adidas Adizero Prime X immediately grabbed the headlines when launched, being one of the first ‘illegal’ shoes for competition under World Athletics rules: but there’s more to this shoe than meets the eye.
Let’s be honest about this shoe, it’s probably as much of a marketing story from Adidas as it is intended to be a commercial shoe.
That said, it’s quickly gained many fans.
We’ll get into the weeds with the intriguing design details, and more importantly, how well this show runs – and figure out if that stack height actually helps your running.
Adidas Adizero Prime X – Overview
The Adidas Adizero Prime X is billed by Adidas as a training shoe to accompany their road legal line up of racing shoes, the Adizero Adios Pro 3 half and marathon distance shoe, and the Adizero Takumi Sen 9, their 5k and 10k shoe.
The Prime X offers additional cushioning to both increase the comfort of the ride over longer training distances as well as help improve the durability of the shoe.
The deep 50mm stack of Lightstrike Pro material is soft and responsive and certainly has that bouncy feel we’ve come to expect from these so-called supershoes.
Embedded within the midsole is the Adidas Energyrod system.
Unlike many brands, Adidas has chosen a system of rods instead of the more conventional carbon plate.
These rods stem from the heel of the shoe and spread out through the midfoot into the forefoot to follow the lines of the foot’s metatarsals.
The brand themselves say the rods ‘limit energy loss’, unlike many brands that refer to their carbon plates as adding a more propulsive element to their shoes.
Ultimately the effect of the rods feels similar to that of carbon-plated shoes, it makes them feel a little springier!
Is The Adizero Prime X Really “Illegal”?
The 50mm stack is the real story here and it’s that deep cushioning that leads me to question the legality of the shoe.
Yes, 50mm is over the stack height limit set by World Athletics but have they measured the shoe and ‘banned it’ or have Adidas simply said ‘hey this is 50mm, it’s illegal’?
It doesn’t appear on the World Athletics shoe list as a ‘banned shoe’, that said, there are no shoes listed that are banned on the list. Should World Athletics be listing illegal shoes as well as legal options?
It can be confusing at the very least, especially for example when this shoe is placed side by side with the Nike Alphafly Next Percent 2, both seem almost identical in the stack height!
For me, it’s the interpretation of the rules and perhaps by a clever recess in the center of the heel, Nike reduced the measured stack of their shoe to within the legal parameters.
Adidas Adizero Prime X – The Details
At 251g (8.85oz) for a Men’s size US9.5, the Adidas Adizero Prime X feels light, especially given you are getting a large amount of cushioning in this shoe.
The Lightstrike Pro midsole is the brand’s lightest and most responsive foam and even with this 50mm stack of cushioning in the heel (dropping 8.5mm into the forefoot) the shoe manages to remain light and feel like a race day shoe.
The Energyrods stabilize the ride a little, but at anything under race pace, the shoe does feel a little unstable due to the high stack and a rather narrow footprint on the ground.
The lateral side of the heel is slightly beveled to make for a smoother heel strike but I only really found this to be fully effective when I reached around 6-minute mile pace.
Below this speed I was very conscious of the instability of the shoe so felt I had to be very cautious.
This isn’t an easy day shoe!
Adidas Adizero Prime X – The Heel And Sole
Outsole coverage is good and in the heel area, more of the midsole is covered than in some shoes such as the Nike Vaporfly, where the outsole rubber leaves a large area unprotected and can lead to early signs of wear in that shoe.
Here Adidas uses Continental rubber, a compound known for better traction and one which I’ve never encountered any issues with even in the wet. The pattern of the sole is simple but a little like a racing car tire for the wet, with a chevron design to expel water away from the contact area between the shoe and the ground.
Adidas Adizero Prime X – The Upper
The upper uses a translucent engineered mesh design manufactured from around 50% recycled materials. These translucent type designs tend to have a generally stiffer feel to them compared to other uppers but here the shape is ok and fits the foot well.
Perhaps the only real issue is that the upper seems rather over-designed in the forefoot area.
Here, around the forefoot and tongue, there just seems to be too much going on, with lace loops incorporated into forefoot straps.
I’d have preferred a simpler design which may reduce that bunching that can often occur in this region when you pull the shoes tighter for racing or faster runs. It’s not a deal breaker, it just seems a little bit like overkill.
The heel collar and Achilles area of the shoe is a more minimalist design with just the slightest padding, but it’s a neat finish so I’ve encountered no issues here. Likewise, the tongue is just a single layer of fabric.
It’s stitched into place on the instep so there’s little chance of movement when on the go, just ensure it’s sitting flat against the foot when you lace up.
Adidas Adizero Prime X – The Run Test
With many supershoes of this type, my first run is usually a treadmill run.
So I set the treadmill to a 6-minute mile pace after an initial warm-up and away we went.
Perhaps what was most telling in the warm-up was when setting off at an 8-minute mile pace the shoe did feel unstable, wobbly in fact.
Even when jogging I just couldn’t get comfortable in the shoe.
I crept the speed up gradually for the first mile and it was only once I got close to 6:30 miles that the earlier instability began to fade and my confidence in the shoe increased.
Once at ‘tempo’ pace, just outside my marathon race pace things felt altogether better. With a faster cadence and more efficient foot strike the shoe came into its own.
The soft cushioning and springy ride really began to shine and the shoe became one of those that bring a smile to your face. The energized feeling often brings a sense of giddiness, where you can imagine die-hard traditionalists bemoaning the death of the shoes of the 70’s and 80’s and their complaints of such cheat shoes.
Throughout my treadmill 5k run the shoe really did feel like a game changer. That said, it’s only a shoe that I’ve reached for since when really felt on my A game. I’ve run a few interval sessions on the roads as well as a couple of longer tempo runs of between 7 to 10 miles.
On the tempo runs, I’ve had no issues except for a couple of sharp turns when the instability lets itself be known again.
On interval sessions I’ve just paid a little more attention to the recovery jogs to keep my feet steady.
Adidas Adizero Prime X : Key Takeaways
In summary, the Adidas Adizero Prime X can’t be used on race day. Or at least not by athletes that may be chasing qualifying places on International teams or official records.
Again, this area can be confusing so it is, as always best to check with national governing bodies for specific rules if you area gunning for a record.
So when will you use the adidas adizero Prime X?
Well for me it’s become a rather specific tempo running shoe.
In marathon build-up phase it’s ideal for that long race pace effort run and results in a smooth, efficient, and energised ride that leaves my legs feeling pretty fresh the following day.
It’s great at shorter distances too, I’m just cautious of the stability so have tended to favor it for treadmill intervals where I don’t have to concern myself with turns in the road and uneven surfaces.
