Butterfly is perhaps the most physically demanding stroke. It is also the newest of the four strokes and was first swum in its modern form in the 1956 Olympics. Before that, butterfly was swum using the breaststroke kick. Butterfly requires the simultaneous overhead stroke of the arms combined with the dolphin kick. The dolphin kick features both legs moving up and down at the same time. If the swimmer does a flutter or breaststroke kick, it results in a DQ (disqualification). As in the breaststroke, the swimmer must touch the wall at the turns and at the finish with both hands simultaneously. After the start and after each turn, the swimmer is permitted any number of underwater kicks but only one underwater arm pull. That pull must bring the swimmer to the surface.