What is believed to be the world's first 'doughnut'-shaped sole concept based on biomechanical research and featuring tailor-made polyurethane technology from Huntsman Polyurethanes has been created in France to deliver a running shoe that retains its spring and has longer-lasting performance.

The new Circular System sole technology from Decathlon - the world's third largest distributor of sports equipment with a chain of 252 self-service department stores in 11 countries - has been introduced into two models of a high performance fashion running shoe under its Domyos brand. Resulting from a study of movement and the foot's constraints at the Decathlon research centre in Villeneuve-d'Ascq, the concept is characterised by a ring-shaped geometry under the heel, where a central hole allows for a three-dimensional, inward and outward distortion, reducing the shock.

When people run, each step sends a measurable shock wave through the whole body. Fatty tissue under the heel bone acts as a natural protection, but has limited damping capacity. The sole design maximises the efficiency of this natural cushion.

Independent testing by a biomechanics laboratory is said to have shown that the Decathlon Circular System absorbed 21 per cent more energy than other running shoes.

Nicholas Bouché, R&D project manager at Decathlon says: "Studies have revealed that most jogging shoes lose a great deal of their damping capability after only 200 kilometers - a distance quickly covered by serious runners who train several times a week. The Circular System is a prime example of our philosophy to design better sports items which are good for the user's health, well-being and pleasure."

To develop its product, Decathlon collaborated with Huntsman Polyurethanes for a suitable soling solution. The company created a bespoke waterblown polyester system based on its Suprasec 2544 prepolymer technology adapted to the climatic conditions in Asia where the footwear was being produced. It has an inherent shock absorption engineered polymer to provide the right balance of shock absorption and return qualities achieving the required bounce effect and prolonging the shoe's performance.

The elastomer offers the right balance between cushioning and springiness. The combination of the sole design and the resilient foam guarantees excellent damping efficiency and durability, tested using accelerometer measurements and aging under sustained mechanical impact.

The doughnut-shaped sole was produced in Vietnam by Viet A Chau, the leading unit sole producer in the country.