To spice up a foreboding 800’s workout this morning, I decided to run some of the scheduled repeats in Structure 21 and the rest in my favorite speed shoe, Nike Odyssey 2, to see if the Structure being half an ounce lighter made a difference.
Turns out I still much prefer Odyssey for fast running, and the loose fit of Structure 21’s heel was even more apparent after being reminded of the snug heel fit of Odyssey.
This workout session cemented in my mind that Structure is more suited for mid to long distance runs than speedwork and that the more loose heel really does bother me.
Structure 21 rides very similarly to the ASICS GT-1000 6, with a bit more flexibility in toebox upper fit; the heel fit also gives a touch more room. So all in all, the fit is closest to ASICS’ GT-2000 series.
Beyond the custom-snug fit offered by the lacing system, the Structure has less…structure to it than do the ASICS GT series shoes and the brand’s new Dynamis, with the latter and GT-1000 being about the same weight as Structure 21.
Structure is also a competitor to the Saucony Guide, Brooks Adrenaline GTS, and the Mizuno Wave Inspire. You’ll get a similar upper fit from these shoes, but the differences in offset provide varied underfoot experiences.
Saucony Guide is 2mm lower in heel-toe drop with 8mm as opposed to Structure and GT-2000’s 10mm, with Adrenaline and Wave Inspire coming in at 12mm.
A lower drop seems to encourage runners onto their toes while at the same time limits the range of motion of the Achilles.
My podiatrist informed me that one’s preference in drop height of a shoe relates to one’s Achilles flexibility—but no two people are alike in terms of an exact “if this then that” diagnosis: you’ll have to try out a few different types to see what really works for you.
Nike Zoom Structure 21 General Info
My first impression of Structure 21 was that it’s a shoe with a flat insole (I like at least a little more arch) that was otherwise unremarkable (which isn’t always a bad thing). The midfoot upper really snugged up nicely, though—that surprised and impressed me.
I found that I could get a very similar fit in my normal size and in the half size up, the difference coming down only to length.
Structure fits true to size, but my slightly bigger foot likes to consider the half size up. I stuck with my usual size for Structure, but if you prefer more room for your toes, you’ll want to size up.
Nike Zoom Structure 21 Sole Unit
Like it or leave it, Nike kept the sole unit completely the same as the 20 in this new model: a dual-density mix of Phylon and Cushlon foams.
The foam is softer on the lateral (external) side of the shoe and thanks to Nike’s Dynamic Support, gets harder on the medial (internal) side.
The 21 is my first experience with the Structure line, so I asked a friend of mine who loved the 18th and 19th models what he thought of the 20.
In his experience the older versions with the medial cage held up much better than the Dynamic Support in the 20 (and 21), which compressed inward as the miles were added, while the outsole durability remained the same despite its overhaul in structure.
The new midsole made Structure a few mm higher (while maintaining a 10mm drop from heel down to toe height), and ironically, I kept feeling like I wanted the shoe to be closer to the ground, before I even learned about this change.
I’ve enjoyed running in HOKA’S, but for some reason a higher ride in this Nike never lost its awkward feel.
The midsole is not overly soft, yet it’s also thick enough that I don’t give it “ground feel.”
I was pleased with its performance on long runs. In comparison with the Lunarlon foam in Lunarglide 9, with about 70 miles on both shoes, Structure 21 did maintain less of a dip in the forefoot, a reliable way to check how worn your shoe is.
This means that Structure will hold up for more miles than Lunarglide with its softer midsole. (Take out the sockliner and feel for a dip; smooth means a highly durable (or new) shoe while a significant dip means the shoe is done.)
Nike Zoom Structure 21 Upper Info
All of the color offerings for Structure 21 start with a dark shade in the heel that gradually shades lighter as the shoe moves forward, both for the upper (material and color) and the midsole: this is fabulous!
It actually took me about a week and a half before I realized that the heel of my “black” shoe is black, but the forefoot is a dark navy blue. The material is a one-piece Flymesh fabric which provides great breathability.
After starting with a mediocre heel counter-if your heel is wide enough to fit it well-the upper moves into the section with loop-style lacing that really surprised me by how well it snugs up.
I expected Flywires to do the job better, but Structure 21 holds my midfoot better than Odyssey does with its Flywires.
From there the upper lacks structural components that I appreciate in a stability shoe, such as the thin strips along the toebox area of adidas adizero Tempo 9.
Since there is a low arch in the midsole, I would appreciate an attempt in the upper material to lend arch support, such as the medial panels of ASICS Dynamis, but there’s not much in Structure to grant that benefit.
The thin medial overlay added from the 20 seems to be cosmetic versus functional.
Nike Zoom Structure 21 Conclusions
My favorite aspect of Zoom Structure 21 is the purple fading to blue on the midsole. Also brilliant is the black heel upper that transitions to navy blue in the front.
But since I hail from a day when shoes came in one color, and the running shoe you bought had to be based on function over style, I learned to evaluate a shoe beyond the externals.
In that regard, Structure 21 didn’t seem a bad shoe to me: it’s lightweight, breathable, and offers a snug midfoot along with a wide forefoot platform to counter excess rotation with pronation.
But it also didn’t impress me: loose heel, ride felt awkward. Since the midsole is showing signs of durability, I’m giving this shoe 3.5 versus 3 stars.
If you liked the change in sole unit from the 19 to the 20, you’re probably going to equally appreciate Structure 21.
If not, well, hold out and see what Nike comes up with for the next model. Let us know what you think of the shoe in the comments!
We purchased a pair of Nike Zoom Structure 21 from runningwarehouse using our own money. This did not influence the outcome of this review, written after running more than 50 miles in them.