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Asics GEL Uncovered

April 25th, 2013

Asics GEL technology has been with us since the mid-1980′s, and millions of runners rely on it for cushioning and shock absorption. But what the heck is this stuff? Turns out, this squishy silicone-based compound is more complex than you might think.

We recently took apart an Asics GT 2000 to see what we could find out about Asics’ best-known cushioning technology. Here’s the skinny:

Diagram of Forefoot and Heel Gel Units

Heel Unit

The GEL in the heel of the GT-2000 closely matches what you would think simply by looking at the outside of the shoe. The visible GEL on the outside of the shoe is part of a cohesive piece that moves toward the center of the shoe, where a circular unit of the gel sits right under the heel.

Compared to the visible window in the midsole, the amount of gel actually decreases as you move closer to the center of the shoe. This makes sense, since the GEL here is meant to cushion heel impact forces, and during a typical heel strike, the lateral edge of the heel lands first.

The composition of the GEL in the heel is unique to the heel and is designed to disperse high impact forces and give a cushioned feeling. According to Asics, there are actually a variety of different GEL compositions and densities, depending on the shoe’s intended use. The GEL we uncovered in the GT-2000 is a bit different than that used in the Kayano or Lyte33, for instance.

Cross Section of Asics GT 2000 Heel

Forefoot Unit

The shape and position of the forefoot GEL unit might surprise you (see below). It’s only about the size of a half dollar and close to the same thickness.

But big things come in small packages and this GEL unit does more than its size conveys. Officially known as a Twist GEL unit, it’s located under the head of the first metatarsal, and allows the first metatarsal head to sink slightly below the other metatarsals in the foot. Twist GEL is designed to attenuate shock at toe-off and activate the windlass mechanism (allowing the natural elasticity of the  foot to collect and release tension to propel the foot forward). By letting the first metatarsal head drop slightly, this GEL unit encourages the foot to move more naturally and spring forward. Asics uses Twist GEL in many of its performance running shoes.

The composition of the Twist GEL unit is adjusted compared to the heel unit to give a more lively, responsive feeling. The unit acts more like a spring than a dampener, which makes sense given the need for a responsive toe-off.

Twist Gel Unit Up Close

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  • Steven

    Fascinating, thanks for investigating. I’m surprised the forefoot gel unit is so small. Given the variety in feet shape it’s possible that this small gel piece would not always be positioned under the 1st met head.

  • http://lawking.wordpress.com/ lawking

    Steven, that is what happened to me. The the forefoot gel unit in many Asics shoes always feel ill-positioned to me.

  • David Weeks

    I was frustrated when Asics reduced the size of the forefoot Gel unit in both the Cumulus 14 and the new GT 1000 models. Made for a much firmer and stiffer feel overall.. :+(