Ricky and Serena Rapper, Nelly Noodlehead and Lennart Lindberg, their neighbour, take a vacation at the Muscle Rock holiday village. There, they meet a father and son, Bill and Sylvester Pöntinen, who are training for a strongman competition. Serena and Nelly take a sudden interest in exercising – and in the Pöntinen duo. Ricky and Lennart decide to show that they’re no chickens and ask Aunt Fran to train them for an arm-wrestling competition. It seems that everyone is assuming things about each other – but is Sylvester really just a puff-out, like Ricky thinks he is?