Women run through a field of water, mud and electrified wires during the Tough Mudder 10-12 mile (16-19 km) obstacle challenge in San Bernardino, California, in the United States on Saturday. Tough Mudder is an endurance event series in which participants attempt a 10-12 mile long military-style obstacle course. Designed by the British Special Forces to test mental as well as physical strength, obstacles often play off of common human fears, such as fire, water, and heights.SD-Agencies