The Adrenaline 21 is the newest version of Brooks Go To Shoe (GTS). The Adrenaline 21 has all the great features from the previous version, but it now has extended their DNA Loft Cushioning system from the heel to toe. This makes for the smoothest, softest ride ever!  Brooks’ new Engineered Air Mesh provides a secure fit while improving its breathability. The Adrenaline 21 has Brooks’ GuideRails® holistic support systems which increases the focus from the foot to include the knee. The GuideRails help keep excessive movement in check while keeping you moving in comfort.