The Endorphin Speed 6 Running Shoe carries a reshaped nylon plate and SPEEDROLL geometry that move each stride into the next as the pace rises on tempo runs and speed days. PWRRUN PBX, a lighter and softer foam, adds 2 millimeters more foam underfoot. What Our Gearhead(R) Experts Are Saying:"Through long tempo blocks, the foam softened the impact of the late repetitions, and I held pace to the last one. The cushioning felt consistent from the warm-up miles to the cooldown."