NIKE Men's Air Zoom Structure 21 Running Shoes
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The excessive outwards bias or lean of the older Structures (17, 19) is no longer present on the 21. The rearfoot has a bit of an outer bias due to the midsole groove and the beveled heel, but only slightly so.
The Streak 6 is a lightweight Nike model fitting for shorter road races and distances for up to a half marathon. 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. 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.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 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 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.
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 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. 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. If our memory serves us right, the Zoom Structure 18 was the first Nike running shoe to feature Flymesh. This upper material is made of a single layer of engineered mesh and borrows aesthetics from the Flyknit.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 For reasons best known to Nike, the Zoom Structure has rarely had a plushly padded tongue or heel lining. Thankfully, the Structure 20’s tongue quilting is nowhere as bad as the Structure 18.
When it comes to popularity, the Structure series comes nowhere near the likes of the Pegasus or the Infinity. I personally prefer the Structure to both the Peg and the Infinity because its upper is more padded and the cushioning feels more substantial but I think that most runners still think the Structure is an old school, traditional stability trainer.
An inner sleeve is attached to the tongue, so the arch-band strap is sandwiched between the outer upper and the inner sleeve. The laces are now flat instead of round. These flat laces pass better through the strap-based cinching system. The Structure 21 uses a strapping system (or the internal ‘arch-band’ in Nike-speak) which was also used on the 20.