seconds would be added to their head start. Once a winner was determined, the runner-up was encouraged to finish the course anyway. Each obstacle on the course had rules which were only explained to viewers if there was a potential violation, and if the referee was not satisfied that the contender crossed an obstacle properly, he could demand that they retake it. The first obstacle was originally a cargo net with a steel slide and a scramble sheet. In series 2 this was replaced by high-and-low beams and a rope climb. The high-and-low beams were a set of four hurdles to scale; the high hurdles needing to be scaled while the low ones needed to be rolled under. In series 5, a new obstacle was placed between the high-and-low beams and the rope climb, called the bungee maze which required contestants to climb through a series of elastic ropes. In series 6 this was replaced by a double-sided cargo net with a trampoline at its base; both sides needed to be scaled to pass. The second low hurdle was removed from the course to make room. After the scramble sheet/rope climb, contenders would cross from one platform to another; the females on a hand ladder while males used a hand bike. They then crossed to a third platform by running across rolling beams, which were replaced by trapezes in series 6. After this, contenders would climb a vertical cargo net up to a gantry, where they would take a zip line down to a crash mat on the arena floor. Following this, they traversed a balance beam, which was introduced in series 2. During series 6, the single balance beam was replaced with two seesaws. Each had a teeter-totter mechanism; the contenders needed to negotiate the obstacle without falling off and had to make certain their feet touched a yellow mark at the end of each seesaw, though this was only a rule during the heats as from the quarter-finals onwards, the yellow mark was not included on the seesaws. The final obstacle was the travelator, which was an incline into which two belts running in the opposite direction of the incline were installed. The object was to scale the ramp while running against the belts. When attempting the travelator, contenders were not allowed to use the covers on either side of the moving belt to help them get up.