Four middle-aged men from southeastern Germany were rushed to the hospital on Sunday after a social media stunt had gone awry.

The men, all aged between 31 and 67, are coworkers at a small company in Tannheim, in Germany's Black Forest region. They were participating in an internet stunt called the "Grill-Pool-Challenge."

The seemingly harmless challenge requires a group of people, usually colleagues, to stage a summer party in the winter, film it and post it on the internet. They will then dare another group to complete the challenge, and if they fail to do so, will have to buy beer and sandwiches for those who challenged them. The stunt, which has been especially popular in Austria and southern Germany, is also meant to encourage donations to local causes.

In one example online, small-town firefighters turned a disused fountain in front of their fire station into a "pool," using scuba diving gear to swim in it, while they grill hamburgers in the falling snow.

For the ill-fated group in Tannheim, however, things did not go to plan. The men constructed a pool in the back of one of their company's flatbed trucks while a fifth coworker backed the truck into the firm's warehouse.

The water began to move so violently that the four men were thrown from the back of the truck onto the concrete several meters down. They were taken to a local hospital for the their injuries.

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