The performance comes from a combination of two elements working together. A stiff, curved carbon fibre plate is embedded inside a deep stack of very light, responsive foam. The plate acts like a lever, helping to roll your foot forward smoothly and quickly. This action returns more energy with each stride and reduces the amount of work your lower leg muscles have to do.
These shoes are built for racing and key speed-focused training sessions. To get the most benefit and extend the life of the shoe, most runners reserve them for race day and their most important workouts, rather than using them for all of their weekly mileage.