Performance is the time (t) to cover a given distance (d), i. e. speed of swimming (v = d / t). In turn, v is the product of stroke rate (SR), and distance per stroke (d/S). Maximal v is set by maximal metabolic power (E'max) and energy cost of swimming (Cs). Drag (D), efficiency (n) and v set the metabolic requirements. D can be partitioned in friction (22%), pressure (55%) and wave (23%) drag. D reduction can be achieved by training and swim suit design. _ and Cs are influenced by D, by the energy wasted to water and by the internal work. E'tot is a combination of aerobic and anaerobic power: it increases monotonically with the speed, is highly variable and, it decreases with training. Aerobic, anaerobic lactic and alactic energy supply 38, 43, and 19% in 200 yd and 19, 54, and 26% in 50 yds. At competitive v, Cs is lowest in front crawl and higher in backstroke, butterfly and breaststroke (in that order). The above mentioned factors are highly variable, but even among elite swimmers each is highly trainable.
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