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Participants of the "Tough Mudder" endurance event series run through the "Mud Mile" obstacle in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

A participant of the "Tough Mudder" endurance event series crawls out of the "Electric Eel" obstacle in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

A participant of the "Tough Mudder" endurance event series sticks out his tongue after passing the "Mud Mile" obstacle in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

Participants of the "Tough Mudder" endurance event series run through the "Electroshock Therapy" obstacle made of electrical wire holding some 10,000 Volts in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

A participant of the "Tough Mudder" endurance event series reacts as he runs through the "Electroshock Therapy" obstacle made of electrical wires holding some 10,000 Volts in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (12 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

A participant of "Tough Mudder" endurance event series jumps into a tub filled with ice-cubes at the "Arctic Enema" obstacle in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

Heather Cozad (R) of the U.S. drinks beer with a friend after finishing the "Tough Mudder" endurance event series in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

Participants of the "Tough Mudder" endurance event series runs are seen with mud-covered faces after clearing the "Mud Mile" obstacle in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

Participants of the "Tough Mudder" endurance event series run through the "mud-mile" obstacle in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

A participant of the "Tough Mudder" endurance event series runs through the "mud-mile obstacle" in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

Heather Cozad of the U.S. warms up for "Tough Mudder" endurance event series in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

Participants of the "Tough Mudder" endurance event series run through the "Electroshock Therapy" obstacle made of electrical wires holding some 10,000 Volts in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

A female participant of the "Tough Mudder" endurance event series jumps over an open fire of the "Fire Walker" obstacle in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

A participant of the "Tough Mudder" endurance event series poses on top of an open fire at the "Fire Walker" obstacle in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

A participant of the "Tough Mudder" endurance event series runs through the "Mud Mile" obstacle in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

Heather Cozad of the United States jumps into the ice-cubes filled "Arctic Enema" obstacle of the "Tough Mudder" endurance event series in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

A participant of the "Tough Mudder" endurance event series struggles in the "Electroshock Therapy" obstacle made of electrical wire holding some 10,000 Volts in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

Heather Cozad of the U.S. runs through the "Electroshock Therapy" obstacle made of hanging electrical wire holding some 10,000 Volts in the finish of the "Tough Mudder" endurance event series in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )

A participant of the "Tough Mudder" endurance event series drinks a beer after crossing the finish line in the Fursten Forest, a former British Army training ground near the north-western German city of Osnabrueck July 13, 2013. The hardcore but un-timed event over 16 km (10 miles) was designed by British Special Forces to test mental as well as physical strength. Some 4,000 competitors had to overcome obstacles of common human fears, such as fire, water, electricity and heights. REUTERS/Wolfgang Rattay ( GERMANY/ )