Koch was taken to the University Hospital of Dusseldorf, where his injuries were reported to be serious.
The popular program shows people attempting unlikely feats as celebrity panelists predict whether they will succeed or not.
Koch, a gymnast, was wearing a chest protector, kneepads, a helmet and "kangaroo boots." He had four minutes to somersault over five cars.
He succeeded at the first jump, balked at the second and landed on his face as he lost his balance after jumping over the third car, which was driven by his father, Christopher.
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