STREAMLINING FOR SPEED - 19TH CENTURY EXPLANATION
"The scientific side stroke swimmer, when at the height of his speed, also presents the least surface practicable of his body to the opposition of the medium through which he is cleaving his way. The figure of the shark, cod, salmon. etc., is said to closely approximate to that which is considered by mathematicians to offer - and, consequently to receive the least resistance in its progress through the water."
"Now the attitude which the human body assumes in the side stroke, also more closely approximates to that form than it does in any other style of swimming. It is also admitted that the strain upon the chest is considerable in breast swimming, while it is rarely felt at all in side swimming. How, with all these advantages in favour of the side stroke, the swiftest swimmer can rarely get through the water at double the speed of a very indifferent one, is an anomaly which requires explanation."
Charles Steedman, Champion of England and Victoria, Australia, writing in his 1867 "Manual of Swimming".