The first competitor swims 50 m freestyle without fins.
The second competitor swims 50 m freestyle with fins.
The third competitor swims 50 m freestyle pulling a rescue tube and after having touched the wall, passes the harness of the rescue tube to a fourth competitor who wears fins.
The third competitor, playing the role of "victim," holds the rescue tube with both hands, while being towed 50 m by the fourth competitor to the finish.