Lucky 13 is our best Adrenaline GTS yet. We paid special attention to the underfoot flex by adding Omega Flex Grooves & continuing Omni Grooves in the forefoot, allowing the outsole to bend & shape naturally. Continuing with the tradition of tailored fit, stretch eyelets lock into the medial side to capture the foot better & technologies like Flextra & anatomical Brooks DNA deliver customized stability & cushion. No luck here, just purely good design. Technology: Flextra-elements are strategically incorporated into the outsole in the forefoot area. These elements are designed depending on gender & weight to provide the necessary forefoot stability. Flextra is a system of individually configured flex grooves. It guarantees every runner ideal forefoot flexibility independent of weight & gender. Our product developers differentiate by using three different flex groove designs. The less outsole material is being utilized the more flexible the shoe becomes. The new mids