The Brooks Women's Glycerin 21 is a neutral running shoe that combines plush cushioning with adaptive support, offering a luxurious and smooth ride. Engineered with a DNA LOFT midsole, it delivers premium softness underfoot without sacrificing responsiveness or durability. The upper is crafted with a 3D Fit Print technology, providing a secure yet flexible fit that conforms to the foot's shape. The Glycerin 21 is ideal for runners seeking maximum comfort and cushioning for long-distance runs.On the other hand, the Brooks Women's Glycerin GTS 21, also known as the Glycerin "Go-To-Support" version, is designed for runners who require added stability and support. It incorporates GuideRails technology, focusing on guiding and supporting the body's natural motion, thereby reducing excess movement that could lead to injury. This version maintains the plush cushioning and smooth ride of the Glycerin line while catering to overpronators or those in need of extra stability during their runs.