Adidas Adizero Prime X Strung Review: Insane in the Membrane
By Chief Editor Matthew Klein
The Prime X series have continued to be insane shoes. Debuting with a 50mm stack height in the heel, Adidas was clear on its intention to make a World Athletics illegal race shoe and to get something so outrageous on the market that it would turn heads. Heads certainly turned and ankles were also rolled in the process wearing this shoe. The challenge with the shoes is that they were so inherently unstable that people were either too scared to wear them (ankle roll/fracture) or they were not appropriate. There are many people who have enjoyed this shoe as a super stack training/workout/racing shoe (among the non-elite). The Adidas Prime X Strung is primarily an upper update with a new 3D printed fiber woven strung upper that is supposed to provide unique security to the runner's feet. While it does achieve this, this continues to be a highly unstable, super stack training/workout shoe that comes at a steep cost.
Shop: $299.95 at Running Warehouse
Weight: 8.68 oz, 257 g (Unisex Sizing Men's size 9/Women's size 10)
Stack Height: 50mm / 41.5 mm
Drop: 8.5 mm
Classification: Ultra Max Stack Height Training/Distance Racing Shoe
RUNNING SHOE SUMMARY
The Adidas Adizero Prime X Strung is a super stack training/racing shoe for those who want a massive amount of shoe underfoot, Energy Rods, Energy Blades and a lightweight upper 3D printed upper. A new 3D printed Strung upper provides increased security at the heel while a slightly long fit provides a surprising amount of width up front. An aggressively tall stack height and narrow width create a shoe that works best when you are moving forward with zero ground feel and a stiff but highly bouncy transition. Those that want maximum protection, no stability and an incredibly light weight for such a massive shoe for daily training, workouts and long-distance racing at a non-elite level should check out this shoe if money is no objection.
SIMILAR SHOES: Asics Superblast
Based on weight and stack height, the ASICS Superblast is the most similar shoe on the market to the Prime X Strung. While both feature somewhat similar stack heights, the Superblast is far more stable while the Prime X is absolutely not. The ride is far stiffer in the Prime X and stays that way, whereas the Superblast tends to break in and transition nicely. The Superblast continues to be a lighter shoe, although not by much. The material underfoot is bouncer in the Prime X, but is better balanced in the Superblast. The Superblast works as a great training and workout shoe, whereas the Prime X Strung can be a daily trainer but leans far more in the aggressive workout and racing category of shoes.
FIT
The Adidas Adizero Prime X Strung fits me slightly long in my normal men's US size 10. I used a size 9.5 in the previous version and while it was just slightly tight, the 9.5 worked a bit better. I would suggest sizing down a half-size for those who are between sizes or who want a snug performance fit. Those who want more room, particularly in the forefoot, should stay true to size. The Strung upper works well to provide additional structure in the heel without a traditional heel counter. The fit is slightly snug in width in the rearfoot with no additional padding. All security comes from the woven 3D printed structure, which actually does a decent job of keeping things locked down (I did not have to lace lock the heel). The midfoot fits snug with an extremely thin, free-floating tongue. Fortunately, this is linked to the laces, but I did have to make sure the tongue laid down flat every time I put the shoes on or I got bunching. The forefoot fits wider and slightly long. I found the fit did better with thicker socks as it took up some of the extra volume found up front. This may be due to the slightly longer size, but I did get some crinkling in the upper which caused some pressure on the tops of my toes. This is despite the higher volume, and I again found thicker socks fixed this issue. The width up front is slightly wider with room to splay the toes a bit. This is a shoe that necessitates socks due to the previously mentioned sizing and while the strung upper creates structure, it is quite scratchy against the skin. It still sits well against the foot with socks on, so those looking to experience a unique 3D printed upper that provides a snug fit in the heel and a longer/higher volume fit up front may enjoy this shoe.
PERFORMANCE
The Adidas Adizero Prime X Strung is a super stack height, plated shoe for daily training, uptempo workouts and long distance racing. The ride is soft, bouncy and unstable in the heel. It is incredibly wobbly at first and biased laterally, so anyone interested in this shoe that is a rearfoot striker will need to approach cautiously. This transitions through a stiff midfoot and forefoot. Due to the slightly long fit, the stiffness in the forefoot became more apparent unless I was wearing thick socks that made the shoe fit more true to size. The forefoot transition allows no toe movement/little ankle movement, so most of the forward drive will come from your knee and hips. There is quite a bit of toe spring and your toes will be held in extension. If you do not have adequate upward motion at those joints this may be a problem. Though there is an 8.5 mm heel drop listed, due to the amount of midsole compression it feels more like 5-6 mm. The outsole traction is fine on road but should not be used on anything but smooth pavement or track. Trails are not an option and even uneven roads are a nightmare. The durability of the outsole has been fine after 30 miles and surprisingly I have experienced little wear if at all.
Use-wise, the Prime X Strung is best as a lighter but maximal daily training shoe and an uptempo/tempo shoe. Those interested in racing in this will find it works best at marathon pace and above. The excessive amount of Lightstrike Pro provides an extremely bouncy ride that feels great at steady efforts. Anything faster than marathon pace efforts feels awkward and almost like the shoe gets in the way. I have tried several fartlek workouts and found it difficult to move into faster gears. The time it takes for the midsole to compress and the size seems to restrict it from this. Easy efforts feel fine outside of the inherent instability and stiffness, but the Prime X can handle them. Long runs are solid outside of the fatigue I experience from the inherent instability (those with more stable mechanics than myself will do fine). So those who want a super maximal shoe for daily and long runs, uptempo efforts or marathon races and beyond may be interested in this shoe.
STABILITY
The Adidas Adizero Prime X is not stable in any form. There are no forms of traditional stability, although plate does exist in the rearfoot to supposedly stabilize motion. The rearfoot features an aggressive posterior lateral bevel, which combined with incredibly soft foam can aggressively pitch the ankle laterally on heel strike. The heel is on the thin side while being at least 50mm tall with a ton of soft Lightstrike Pro. This make landing at the rearfoot feel like trying to land a jump on a balance beam. The midfoot is also quite neutral thanks to the narrow shape and cut-out. Fortunately, the stiffness of the plates and blades help me here, but anyone with stability needs at the midfoot is going to get pitched medially or laterally. The forefoot is not terrible stability-wise thanks to the energy blades and rods creating such a high level of stiffness. The relatively narrow platform for the stack height still makes it neutral at best up front, so those with any stability needs should avoid this shoe. Those who want a tall stack height with a stiff ride that features no side walls or stability methods that have a high degree of control both medially and laterally will enjoy a shoe that doesn't get in their way. Those with stability needs, especially laterally, should absolutely avoid this shoe due to a serious risk of injury.
Thoughts as a DPT: The Fallacy of More
By Chief Editor Matthew Klein
While I understand the Prime X Strung is a unique product with an even more unique upper, it demonstrates the fallacy of more being better. There is a balance to the amount of stack height you can add to a shoe. The taller you get, the more aggressively the shoe needs to be rockered, more stiffening agents are needed to facilitate a forward transition, and if you want to keep the shoe inherently stable, the wider it needs to be. Adidas skipped the last one in favor of lower weight with more stack height. While the foams are one of the larger players in the increasing running efficiencies among fast shoes recently, the geometry and inherent stability with these foams also play important roles. We also know that more stack height does not necessarily provide more protection and while it may functionally increase the lever arm of the limb, that still requires more force from the proximal muscles to get the body over the limb (Burns & Tam, 2020; Kulmala et al., 2018). Maximal shoes shifts work away from the ankle (nothing your ankle can do with 41.5mm/50mm underfoot) and requires much more knee and hip torque and control to use. The hip extensors (glutes and hamstrings) while have to work quite a bit harder to move that longer limb underneath it while also trying to stabilize such an unstable platform (Strang et al., 2016).
While these shoe types shift work away from the ankle, the excessive frontal plane instability at the heel is still a risk factor for Achilles tendon and posterior tibialis issues. So while this shoe may work great for the small population that has great hip and knee strength/control and who want as much underfoot bounce as possible, most people are not going to do well with such a large unstable shoe. This makes this shoe a great example of how the extremes of more are not necessarily better as the shoe is a system that is the sum of its parts, not just one component.
Sources:
Burns, G. T., & Tam, N. (2020). Is it the shoes? A simple proposal for regulating footwear in road running. British Journal of Sports Medicine, 54(8), 439-440.
RECOMMENDATIONS
The Prime X series is like a concept car. It looks extremely cool and are super expensive, but functionally should not be used by the public. Especially for the price, this shoe is such a niche product in its design that it could even be dangerous for certain people. For $300 I would expect far more out of this product. I did not find it overly fast and struggled to run any faster than tempo pace. While I understand this isn't a super speed day shoe, for $300 with rods, blades and that much Lightstrike Pro I expect it to do everything. It doesn't. I would also expect a far better stability design and to think that you can just tie down the foot more with the upper while keeping the same unstable platform is laughable. The Prime X development team have a huge opportunity as shoes like the Superblast and even the NB SC Trainer have sold extremely well. There is a market for this product, but its insanely aggressive and unstable design will likely cause the Prime X to lose out to the other more approachable models listed above. Additionally, I have already treated one patient local to Los Angeles who suffered a distal tibial-fibular fracture from rolling their ankle in this shoe (on the road, not trail). So the product is potentially dangerous.
Adidas should take the lessons learned from the well-executed Adios Pro 3 to widen the base of the sole while using geometry, alternative stiffening agents and potentially changing the density of the Lightstrike Pro. This shoe is insanely light for its size at 8.7 oz and trading some inherent stability for a little more weight would make this shoe more useable. Adidas cannot use such an aggressive posterior lateral bevel with such a narrow unstable heel. The amount of lateral deviation I see in runners and patients during initial contact in this shoe is frightening. While I am all for great posterior lateral bevels, this one does NOT work with how the heel and midfoot are set up. The forefoot might be fine, the heel and midfoot width and geometry needs to be reworked to create a more stable platform with a better centrally driven transition not only for comfort but also for safety in a shoe this tall.
WHO THIS SHOE IS FOR
The Adidas Adizero Prime X Strung is for wanting a super stacked ride that can handle daily training, uptempo workouts and marathon races. This is an incredibly unique shoe and tool that will work for those who want as much underfoot as possible in a super shoe (ultra shoe?) with energy blades, energy rods and a 3D-printed upper. Those with any stability needs may not be appropriate for this shoe and/or may be limited to shorter distances, which would be disappointing for a $300 shoe. With this much stack height and bounce, a high level of movement control and stability in the lower extremity are important prerequisites for utilizing this shoe. For those that have those abilities, this shoe provides an incredibly unique experience. The amount of bounce and transition reduces the need for ankle motion while shifting it up to the knees and hips. However, unless you want a unique upper experience that slightly fixes the sizing issue (that is still present), I would find the original version on sale. The original is going for $130-150 in some places now, which is a far better way to try something like this without the risk of a $300 price tag. The Prime X has the potential to be worth that much if some adjustments are made to truly make it stable (not a stability shoe but at least normal), but right now I don't think it is.
GRADING
Matt
Fit: B/B+ (Light close-fitting upper with a slightly long fit that provides a little extra volume and width in the forefoot)
Performance: B+/A- (Extremely unique ride is certainly one of a kind)
Stability: C+ [Neutral] (Highly unstable heel in both directions with a narrow midfoot and soft foam. Not for anyone with any stability needs)
DPT/Footwear Science: B- (While still a unique product, attempting to stabilize the foot with a new upper on such an unstable platform is laughable. I still appreciate everything that went into this shoe and the fact that it is only 8.7 oz, but it is so niche due to the instability. Something needs to be done in the next version to improve stability)
Personal: B- (A unique shoe that has limited use for me given its inherent instability. I would pick the Adios Pro 3 over this shoe a million times and suggest Adidas redo the geometry on this shoe to truly create a more stable/safe ride. The more secure upper feels great but does not offset how unstable the sole is.
Overall: B
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