If you have read some of my most recent reviews (or those from Matt), you will know that we both gravitate towards shoes with some sort of “stability” component to their design. I really liked my first pair of Under Armour Europas (now on pair number two and review HERE) and was curious to try Nike’s flagship moderate stability trainer, the Nike Structure. Matt had tried on a pair (and run in previous versions) and felt that it was very stable in the rearfoot, but wasn’t jazzed about them as he prefers forefoot stability. Granted, this shoe is the workhorse for top tier runners like Shalane Flanagan and Galen Rupp and has stood the test of time (this shoe has been around just over two decades!). The newest iteration of this shoe (the Structure 21) will be a fantastic update to loyal Structure fans and will delight virgin feet (like myself).
Weight: 9.8oz (M size 9), 9.0oz (W size 8)
Stack Height: 28mm (heel); 18m (forefoot)
Widths available: B, D, 2E, 4E
Classification: Moderate Support Daily Trainer
One can appreciate the “dynamic support” midsole design of the shoe. The yellow foam is the higher durometer midsole material that tapers from medial to lateral. Note all the salt stains from running on winter roads.
The fit of the Structure 21 in standard width will be comfortable for most. It holds the foot securely from heel to midfoot and allows the perfect amount of forefoot volume. Therefore, if you have a normal width foot, the standard D width will be perfect. I tried on the D width in store and found it a bit too volumous (but if you have read my other reviews, you will know I have VERY narrow feett). Luckily, these come in narrow (B width) and they fit perfectly. The heel counter is firm, but has enough padding to prevent it from being obtrusive. The foot is held securely over the midsole with a midfoot saddle and inner mesh bootie that is part of Nike’s “dynamic fit” and “dynamic flywire.” I am personally not a fan of flywire and am glad that Nike reduced the use of it in this version of the Structure. The top of my foot was irritated by it at times when I ran in the Terra Kiger and found that it is because the laces dig into the foot during the gait cycle. Instead, the upper material is made of an engineered mesh material (Nike’s “warp-knit mesh”) which is smooth against the foot and offers a snug irritation free fit.
The heel collar is rigid, but well padded. Anyone looking for excellent hold and control of the posterior aspect of your foot will be happy with these shoes. Also, you can see how there are two eyelets of flywire. I do the lace loop trick to take pressure off the flywires on the top of my foot. It has nothing to do with fit. I just really can’t stand flywire.
All together, the upper does a tremendous job of working in tandem with the midsole to give, (wait for it) STRUCTURE for the foot during the gait cycle. There is no horizontal movement of the foot and the heel is locked down. This is perfect for people like me who have excessive mobility of the rear half of their foot and/or ankle, as it slows the amount of pronation and keeps the foot centered over the midsole unit. I feel that many shoes miss this aspect of running shoe design in that they neglect in making the upper provide stability (I’ll let Matt throw some fuel to the fire here). It would be like placing snow tires on a Lamborghini and expecting this rear wheel drive, sports car, to be able to drive on snow. It is just not going to work and will cause problems! In regard to the stiff heel counter, I would caution those with sensitive Achilles as the heel counter is internal. As I mentioned previously, Matt Klein did not like this shoe or similar shoes with this design feature (Brooks Asteria and many Asics models to name a few). Matt is someone who has extra mobility in his forefoot and benefits from a stable forefoot design (hence his love of the new Skechers Forza 3 and his like of the Adidas Tempo 9). I will compare these elements to the Under Armour® Europa at the end of this review. (Editor's Note: I have a weaker peroneus longus than I would like, which causes some instability at the forefoot. I have a solid rearfoot, so excessive rearfoot stability does not tend to work with my feet. Dr. Kollias has the exact opposite, so rearfoot stability/posting works very well for him. Whereas I tend to prefer forefoot stability, which is somewhat rare in the footwear industry but is becoming more common. See my post on forefoot stability HERE).
The midsole is dual density and is made up of Nike’s Phylon and Cushlon with a zoom air unit located in the forefoot. The heel is decoupled with a crash pad (I never really understood this technology, but if you want to geek out here is a link https://www.google.com/patents/US8082684) (Editor's Note: Crash Pads were very common in the late 90s and into the early 2000s. The intention was to absorb shock during heel contact with the thought that decoupling the heel would allow for more shock attenuation. We are still not sure if this works but some people do well with it) and the outsole is made up of durable Duralon Blown rubber in the forefoot and BRS 1000 carbon runner for traction. The overall platform of the shoe is semi-straight with a wide base, which lends to an inherently stable nature. There are also flex groves placed in the forefoot of the shoe, which follows the anatomy of the foot. Many shoe companies place a flex zone right in midfoot, which is counter intuitive as that part of your foot should not flex like your toes or ankle. The geometry of the midsole appears to be based off a varus wedge design and not the typical rigid medial posting or T-beam design seen in traditional stability/motion control running shoes. From my understanding, the midsole is of a higher durometer on the medial side and slopes laterally to a lower durometer (i.e. softer foam) along the lateral aspect of the shoe. Furthermore, Nike also made the firmer foam slope up to just behind the metatarsal heads of the forefoot providing decreasing guidance for the foot from heel to toe. Again, this is not a common design element in the majority of stability shoes (the only other shoe that I can think of is the new Skechers GoRun Forza 3), but lends to a very stable riding shoe.
The darker gray is the higher durometer midsole material. You can somewhat appreciate the change from gray to white and how there is a progressively thinner amount of gray going up along the medial forefoot. The overall footprint of this shoe is wider (Especially at midfoot), which equates to a larger landing zone. The forefoot lugs are very grippy and appear just as tough as those found on the Pegasus.
So what do all these design elements add up to? For one, the midsole design works in harmony with the upper. The secure heel and midfoot allows me to benefit from the dual density midsole, because during the landing phase, the rate of pronation is slowed down and the foot is guided into a neutral push off. When I run in these shoes, I can appreciate the extra sensory feedback the midsole gives versus running in a strictly neutral shoe. I feel the slight bias forces my foot to sink a little more on the lateral side, slowing of the inward roll of the posterior aspect of my foot, and how I am able to push off from all my toes evenly. In strictly neutral shoes, I tend to have excessive pressure placed on my big toe leading to irritation of my hallux longus and likely contributed to my tendinopathy that took me months to recover from completely. I also feel that the rigid posterior structure and flexible forefoot of the shoe aids in dampening the forces on the metatarsal heads of the toes. The Structure 21 not having obnoxious toe spring (I cannot stand it!), flexibility, and a responsive forefoot achieves this! This allows the runner to utilize their natural forefoot rocker (Matt can add his expertise HERE in his discussion on toe spring and the forefoot rocker) and gives a firm, stable platform to push off from (thank you zoom air). I think this is why when I tried the Nike Pegasus 34 I did not like them, as the midsole is too soft in the heel and the zoom air in the heel makes for a less stable landing. I will echo what Matt has said before with our shoe reviews, “Too soft of a midsole equates to greater instability.”
Overall, these shoes have been a joy to run in. They have a very smooth transition from heel to toe with a nice pop at toe off. They do run on the firmer side, but they have plenty of cushion as a daily trainer and for long runs (I’ve done up to 16 miles at a time in these without issue). Oh, and the traction is fantastic! I have fun in slush and on icy roads without slippage (I live in Up State New York).
In terms of durability, these should last around 400-600 miles easily. Just like the indestructible Pegasus, the outsole rubber and midsole foams will hold up nicely. I already have over 200 miles on my pair and see little wear and the midsole cushioning is holding up nicely.
Dr. Klein's thoughts as a DPT:
Dr. Kollias has touched on several things I normally discuss including forefoot stability, toe spring, sole firmness and more that all affect the ride and stability of the shoe. One cannot make blanket statements about how these will affect people given human variability. That being said (and the companies whom I consult for will have heard me say this a thousand times) it is always best to try to work with the foot, rather than against it. That means trying to follow similar principles of biomechanics that the body naturally moves towards. Fighting them generally causes more issues, so it is best to work with the foot and guide it.
Image from semanticsscholar.com The photo demonstrates the subtalar joint axis and how it can deviate based on different mechanics or the position of the foot.
A unique feature that I really like about the Structure 21 is that the wedge/posting (Nike has done somewhat of a combination as Nathaniel mentioned given the material does compress but is slanted with a lateral bias) does follow the subtalar joint axis to a degree. If you look at the bottom of the shoe, you can see the grey material (posting) slant medially. This is different from the flex groove you can see running down the middle of the shoe. This is supposed to help guide the foot forward and is a common feature that Asics is particularly known for. (Whether it actually works.... we are unsure. More public research is needed). The subtalar axis is where inversion and eversion occur, which are important parts of pronation and supination. The joint is the meeting of the calcaneus and talus. The actual axis varies depending on the person (see the photo above regarding deviations) and is part of what makes each individual's foot progression angle (progression from heel contact to forefoot) unique. The problem most companies have is that they may ignore this and try to set up stability in the sagittal plane (front to back). The joints of the foot and ankle really do not work perfectly in traditional planes, especially in the rearfoot. The subtalar joint for example usually lies ~40 degrees superior to the sagittal plane and 16-23 degrees off the transverse plane (Neumann, 2012). This complicates things as those values vary on the person. This is one of the reasons certain stability (and non-stability) shoes work for some people and not for others. It depends on whether all the flex grooves and lines match up with your foot, the shape and your unique movement. The simple way to get around this is to just try shoes on and see if they fit. While that may seem basic, a great deal of research has shown that many people will self-select the best running shoe for them. It helps to be a little educated though on what to look for. So find a shoe that fits your foot well, feels comfortable, smooth and doesn't get in the way of your running.
Room for Improvement:
This shoe is solidly made, and I can see why the top marathoners for team Nike train in them. I would like to see the removal of the fly-wire completely if possible, as I do not feel that the few add any value to the fit. I would also be interested to see if they could incorporate the Zoom X foam into the Structure 22, which will also give the added bonus of dropping some weight. Oh and Nike, can you please offer some more colors in Men’s narrow please? Thanks!
This shoe meets the expectations of its namesake and provides runners needing a little bit extra stability a stellar daily trainer. Nike did its homework when designing this shoe. Paying attention to the little details all add up to a great shoe.
Under Armour Europa vs. Nike Zoom Structure 21:
This is honestly a tie between the two. There are aspects that I think that both shoes achieve and areas where improvement is needed. For one, I appreciate the little notch in the external heel clip on the Europa. It allows movement of the Achilles without restriction, but still supports the ankle. The forefoot fit of the Structure is a better hold versus the Europa were some sloppiness can occur in longer runs when the material loosens up. I will an extra point to Under Armour, because there is more colors available that fit my narrow foot. This is because the last of the Europa runs narrow in the heel and midfoot.
Europa feels bouncier from heel to toe, with the Structure having a smoother transition from a softer heel to firmer forefoot. The forefoot though is more flexible in the Europa, whereas the Structure is stiffer which lends to the pop at toe off. I am finding myself favoring the Structure during runs greater then 10 miles and I think the firmer forefoot helps (remember, soft equals less stable). Overall, both have smooth running midsoles for daily trainers.
You can see a more traditional posting system utilized in the Europa. It works in this shoe though as I have tried on other shoes with this design element that have not worked for me.
Europa wins this for creativity of really incorporating the upper with the midsole to create a stable riding shoe. Yet, I like the midsole slightly more in the Structure and I think it has to do with how well the dual density foam works. The Europa has a more traditional post, which makes a firmer medial heel region. This contrasts with the Structure where one doesn’t fully appreciate a define region of firmness, as the stability is progressive, with it tapering from the heel region to the forefoot. They both work in my opinion, just a little bit differently.
They are almost identical here. The fact that both are stability shoes under 10oz for a size 9 is a HUGE plus. I also feel the price is fair for how many miles you will get out of these shoes. Overall though, both shoes are well done!
Thanks for reading and don't forget to tack on!
Editor's Note: As always, the views presented on this blog belong to myself or the selected few who contribute to these posts. My blog should not and does not serve as a replacement for seeking medical care. If you are currently injured or concerned about an injury, please see your local running physical therapist. If you are in the Los Angeles area, I am currently taking clients for running evaluations.
Currently Dr. Kollias has 231 miles on his pair of Nike Structure 21s. We put at least 50-75 miles on trainers and 25 miles on racing flats prior to reviewing them. If you are a footwear rep looking for footwear reviews or consultations on development, we are currently looking to partner with companies to assist, discuss and promote footwear models. Partnership will not affect the honesty of our reviews.
Dr. Matthew Klein, PT, DPT and Dr. Nathaniel Kollias, DVM, MPH
Orthopedic Resident, Laboratory Animal Resident
***Disclaimer: These shoes were purchased for their full US retail price. We put at least 75 miles on trainers and 25 miles on racing flats. Currently Dr. Kollias has 80 miles on them.
Neumann, D. (2012). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation - Second Edition. St. Louis, MI: Mosby Elsevier
Noakes, T. (2003). Lore of Running - Fourth Edition. Champaign, Il: Human Kinetics
Perry, J. (1992). Gait Analysis: Normal and Pathological Function. Thorafare, NJ: SLACK Incorporated.
Richards, C., Magin, P., Callister, R. (2009). Is your prescription of distance running shoes evidence based? British Journal of Sports Medicine: 43(3): 157-158. doi: 10.1136/bjsm.2009.058453
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