Humans are mediocre sprinters at best. The top speed of Usain Bolt can be matched by a domestic cat. But when it comes to endurance running over many kilometers and long durations of time, very few animals measure up to humans. We present here evolutionary evidence for endurance running in the genus Homo and its impact on the evolution of our body. Given that humans may have run long distances well before the invention of the modern running shoe, we wondered how endurance runners without shoes cope with collisions of their foot with the ground during running. Each foot collides with the ground approximately 500 times per kilometer, with peak ground reaction forces of up to 3 body weights per collision. We present evidence that habitually barefoot runners often land on the fore-foot before bringing down the heel. In contrast, habitually shod runners mostly land on their heel first. We find that the running style of habitually barefoot runners leads to a much lower impulse, and present simple mechanical reasoning for this observation.