Robots joined humans in the field at the Yizhuang half-marathon in an historic first. A total of 21 humanoid robots competed alongside thousands of runners in Beijing, China on Saturday. 3 Robots raced against humans for the first time at a half-marathon in China Credit: Getty 3 The humanoid robots competed in the Yizhuang half-marathon on Sunday Credit: Reuters It is the first time the robots have raced against human athletes after weeks of testing. They had previously completed marathons alongside other runners in China, though. The robots were built by Chinese firms DroidVP and Noetix Robotics, with their sizes…