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. The firm ride quality is distributed evenly from heel to toe, so the progression feels smooth and efficient. The outsole also has the center groove and the side ‘crash rails’ with multiple grooves – features which also assist transitions.

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. The Structure has a firm ride, so the Lunarepic Low makes a good rotational choice as a softer shoe. The ride is cushioned yet supportive, making the Lunarepic suitable for longer runs. The upper has a narrower feel due to the Flyknit upper. The Structure 21 has a softer interior feel than the 18, 19, and 20 due to the updated mesh which also has better breathability. RIDE QUALITY AND BEHAVIOR A new heel clip adds an extra element of heel support to this year’s Structure. This is a feature that we’ve seen on the Infinity Run series for many years. This year’s InfinityRN 4 doesn’t have it anymore.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! 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 could feel the airbag under the forefoot which has always been a characteristic of the Structure series. It was comfortable right out of the box and didn’t need any break in period. The rearfoot rides flat because there’s nothing there except for the dual-density foam and the outsole. Though the open foam area below the heel plus the removable insole helps with the cushioning, the rearfoot is noticeably firm. Forefoot strikers will find the ride to be very responsive due to the large Zoom Air bag. Conversely, heel strikers will experience a flat and unresponsive rear-end. A Zoom Air bag also makes the forefoot stiff so runners who want a flexible shoe should bear this in mind.

The Structure 25 won’t be staying in my rotation. It’s a decent running shoe with a good price but I’m not a fan of the prominent arch because of my flat feet. I prefer other stability features like a wide base or a plate. I also find that it has a flat, boring ride like a shoe from 6 years ago. 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. Both the tongue and heel are moderately padded. However, runners who’re switching to the Structure from brands such as Saucony and Brooks will notice the utilitarian feel of the Structure. I’ve enjoyed running in HOKA’S, but for some reason a higher ride in this Nike never lost its awkward feel. Instead, what you see here are staple models which have long represented the mid-priced support category. The GT-2000 5 (now going on 6) is Asics’s stability shoe with a medial post (Duomax).There’s plenty of outsole rubber, the midsole is relatively firm, and the upper is sleeved and double layered. These attributes help make the Structure durable. The Structure is Nike’s support shoe with a traditional design. This means that the dual-density midsole has a very firm inner side and a slightly less firm outer side. The Structure 20 balanced the two different levels of firmness extremely well. The Structure 21 has an identical midsole, so the ride exhibits the same qualities. DESIGN AND MATERIALS An inner sleeve is attached to the tongue, so the arch-band strap is sandwiched between the outer upper and the inner sleeve. The new Structure is nearly an ounce lighter than its predecessor, thanks to a new knitting technique, with the same magical balance of stability and cushioning—not too stiff but with the added support overpronators need. If you’re looking for a stable, relatively lightweight shoe that can handle a ton of miles, well, you don’t have to look any further. Runner’s World Wear Testers Say The Structure 23 felt like a supportive neutral trainer, not a “true” stability trainer. I reviewed both the Structure 23 and 24 (the 24 was only an upper update). I found them to be the best versions of the Structure to date because they felt stable and supportive without the firm ride or poking arch sensation that you normally associate with stability trainers.

There’s plenty of room in the toe-box and forefoot and the fit is true to size. The Structure also comes in multiple widths (2E and 4E) in case the standard D width fits narrow.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. The Structure 20 simplified the design by toning down the medial post and reducing the number of foam densities to two. The Adrenaline GTS 17 (the 18 is out now) and the Ravenna are two of Brooks’s popular support shoes. The Adrenaline has a higher level of support and firmness than the Ravenna. The Mizuno Inspire 13 is a near-neutral support shoe, whereas the New Balance 860V7 is a cushioned support shoe. The Structure 21 still has Flymesh (as did the 20), but uses a new and lighter version. Nike says that the new Flymesh uses mono-filament yarns which reduce weight yet retain structural strength. The weight claim is true – the Structure 21 sheds nearly a full ounce over the 20. There are other subtle changes, all of them for the better. The upper has larger vented areas. The forefoot breathes better, and so does the rearfoot which now gets vented sections over the Flywire cords.

However, the Zoom Structure 21 is significantly lighter than the 20. The heavier weight of the latter means that users are more likely to suffer from foot fatigue. The Flymesh upper of the 20th version provides structural support while promoting air circulation throughout the shoe. In contrast, the 21st iteration features a lightweight seamless wrap-knit mesh which envelops the foot and expands to mould around the shape of the foot for a second-skin fit. Alternative Nike Running Shoes The Structure 21 is a support shoe with a harder medial post. For this reason, we’ll exclude products like the Nike Lunarglide or the adidas Supernova ST from this list.The Structure’s midsole design has gone through a raft of changes recently. Just over a couple of years ago, the Structure had a quad-density midsole. This included three foam densities of the main midsole, plus the hard stabilizer underneath the arch. The inner outsole is populated with a colony of pentagonal lugs. The rearfoot has a shallow cavity exposing the midsole foam; this extends to a transition groove which splits the outsole longitudinally. The forefoot has an internal Nike Zoom Air bag. 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. We had our work cut out for us last year because the Odyssey 2 was the perfect upgrade path from the Structure. This year, the Odyssey is gone so the only way is down. If you don’t require Structure levels of support, then you should look up the Nike Zoom Span 2. In case if you found the last year’s Structure 20’s ride to be hard on your feet, consider the list of alternatives at the end of this review. PROS AND CONS