The heel has a hard counter which is non-collapsible, and the toe-box has a flexible internal bumper. 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. 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.

I know what Nike is trying to do with the Structure 25 and the latest InfinityRN 4: they want to push runners who need support away from the InfinityRN to the Structure and vice versa. 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 Streak 6 is a lightweight Nike model fitting for shorter road races and distances for up to a half marathon. 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. 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 ShoesThe 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.

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. 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.

Nike Structure 25 Sole Unit

When it comes to support, the Structure 25 is currently the most supportive trainer in the Nike lineup. I’m a mild overpronator with flat feet and I find it stable but the prominent arch is a bit too overbearing. I think it will provide enough support for most overpronators but it’s more suited to runners with high arches.