Starting with the midsole, the Endorphin Speed 4 features the same wonderfully soft and responsive PWRRUN PB cushioning that encases a redesigned winged nylon plate. These two elements work with the SPEEDROLL geometry to deliver a highly energetic and efficient underfoot experience. The winged plate adds torsional rigidity in the heel while maintaining flexibility through the forefoot. This offers the stability runners need for cornering and making tight turns while simultaneously propelling the foot forward. Meanwhile, the PWRRUN PB offers an ultra-bouncy ride that makes track workouts a blast while delivering the protection needed to tackle long runs with ease. In the outsole, the lattice designed rubber layout offers fantastic traction and durability. Despite the technology that's packed into this shoe, the Speed 4 is very lightweight. Helping to keep the weight down is the engineered mesh upper that strikes the perfect balance between being minimal yet secure. The integrated tongue not only helps with lock down, but it is so comfortable that you'll forget it's there. Overall, the Endorphin Speed 4 carries the legacy of its predecessors while adding a bit of flare that elevates it to be a shoe that helps runners push the pace during their hardest training efforts.