Robot athletes including four-legged robot goalkeeper and Google AI ping-pong champion

New video footage emerged this week of a four-legged robot goalkeeper making some impressive saves in a research lab. It's part an exciting scientific field to develop machines that can play sports as well as – or even better than – human professionals. Here, MailOnline takes a look at the robots taking the world of sports by storm, from the six-legged skiier to the ping pong ace and the expert curler. The robot dog was trained using'reinforcement learning' or RL – a subset of machine learning. RL allows an AI-driven system (sometimes referred to as an agent) to learn through trial and error using feedback from its actions. This feedback is either negative or positive, signalled as punishment or reward with, of course, the aim of maximising the reward function.