This photo was taken at an extremely grueling Tough Mudder event.  For those not familiar with Tough Mudder, it's a series of endurance obstacle races designed to test strength, stamina, and teamwork. It’s usually a 6–9 mile course through mud, water, and other obstacles (crawling under barbed wire, ice baths, climbing walls and rope, swimming in mud, electric shock obstacles, etc). It’s team-focused, not a typical race—people help each other finish.