Soul arch
The soul arch is a classic surfing manoeuvre: performed by arching the back whilst riding a wave, demonstrating nonchalance and casual confidence.
Origins
Given that the first surf boards were extremely large, heavy and unwieldy by today's standards, the soul arch may have been one of the earliest 'tricks' available to the rider to demonstrate their style.
The 18th century Hawaiian 'wave sliders' seen, by Captain Cook's crew, performing "dangerous maneuvers" with great "boldness and address", would have ridden 15 foot (4.5 metre) hardwood planks with no directional fin or skeg to aid steering, therefore one of the few expressions available to them may have been the casual stance which would have been a forerunner to the modern Soul Arch.
Development
As longboard design progressed, lighter balsa wood and glass fibre boards with directional fins (or skegs) allowed greater freedom of movement, whilst allowing better riders to adopt more exaggerated stances. Arms raised in the air, hands clasped behind head, signify control and balance and this became a hallmark move. Combined with the difficult 'Hang Five' and Hang Ten moves, when a rider positions at the front (or nose) of a board, a soul arch becomes a significantly more difficult trick, requiring a considerable level of skill and balance.