NIKE Men's Air Zoom Structure 21 Running Shoes

Product Information

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. 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. The Structure 25 is more of a stability trainer than the 2 previous Structure versions. It has an extra heel clip, more arch support and it also has a firmer ride which results in less lean bias.

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. 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 shoe that it reminded me of most was the Infinity Run 3. Both shoes have heel clips as well as prominent arches but the Structure 25 felt firmer than the Infinity Run 3. 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 Structure 20 simplified the design by toning down the medial post and reducing the number of foam densities to two.The outsole rubber is laid out in a familiar format. The outer side has the ‘crash rail’ strip with multiple flex grooves, a design first used on the Pegasus 31. 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. 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. 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 last year’s Structure 20 was an improvement over the 19. Coming to think of it, this should be the case with each update. But given the long lead-times involved in the design and delivery of a shoe, a new model isn’t necessarily an improvement over its older version.

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. From the outside, the Structure 21’s midsole appears to have more than two densities. But that effect is produced by the midsole paint rather than separate foam sections. 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.Overall, the Nike Zoom Structure 20 and 21 are responsive, well-cushioned and deliver an energised ride with smooth transitions. They are engineered to meet the needs of overpronating runners with plenty of midsole foam cushioning to keep wearers stable and support the collapsing arch. Additionally, both models also accommodate users with broader feet by offering wider width sizes for buyers.