BIRKENSTOCK Madrid Birko-Flor Black Buckle Narrow Fit Men。This is is brand new with box. Ships within one business day, typically same day. Additional Details Narrow Width (, S, XN, Schmal, Estrecho, Slim, étroit, stretta) Manufacturer: Birkenstock Material: synthetic Footbed: EVA Sole: EVA Made in Germany and send directly from Germany Sandals Material: fabric-and-synthetic And this is how the Fitness-Sandals work: The relationship between the strap and footbed causes a gripping reflex of the foot with every step taken. During the gripping reflex, both the feet and ankle muscles are tensed, as the muscles responsible for the toe movement are located in the ankles. The muscles are then totally relaxed again when the heel is set down. In this way, there is constant tensing and relaxing of the muscles with every step taken with the Madrid model. Gentle exercise for your feet and legs. In addition, the circulation of the legs is boosted. The model “Ibiza” also has this effect- you can choose either of the models.