All about base excess â to BE or not to BE. In 1948, Singer and Hastings introduced the concept of buffer base (BB). The change in BB from normal was called deltaBB (Î´BB). This change in BB was an expression of the non-respiratory (metabolic) component of an acid-base disturbance.
Empirically from http://www.usaswimming.org/_Rain..., free style is the fastest stroke. This is also called the front crawl (see Front crawl). However as Swimming stroke notes, there are at least 6 variations of that technique.
Front crawl is fastest official racing stroke. I don't know exactly why, in terms of detailed physics, but basically the arm recovery is through the air. So the arm can quickly return to the pulling part of the stroke. Air has less resistance than water, so the more parts of your body that are out of the water, the better. Another factor that makes front crawl faster is that breathing is done by turning the head to the side to take a sip of air.