D'Acquisto, L. J., & Berry, J. E. (2003). Relationship between estimated propelling efficiency, peak aerobic power, and swimming performance in trained male swimmers. Medicine and Science in Sports and Exercise, 34(5), Supplement abstract 193.
There really is no one "best" way for all athletes to swim a particular race. Typically athletes adopt a race strategy, and plan out how they want to swim their races before they actually compete. The optimal race "strategy" varies from swimmer to swimmer. Things like body size, limb dimensions and physiology will go along way in determining the best way for an athlete to swim a particular race.
Peter Vint, Ph.D., United States Olympic Committee and
Russell Mark, M.S., USA Swimming
In 2007, USA Swimming became aware of FINA’s intention to develop and introduce a new starting block design for swimming competitions. There were discussions that the block could possibly be unveiled at the 2008 Summer Olympic Games in Beijing.
Postural deviations are noted in people of all ages, especially from societal transitions: increased sitting and sedentary lifestyles (ask your swimmers how many of them bought call of duty last week….exactly). Many athletes work their ass off and greatly fatigue their muscle causing them to do the exact opposite outside of their sport, hence when they're done with practice they use zero muscles including the postural muscles.
Track, two footed, sling shot, and lean forward are various starts swimmers utilize. The optimal start has yet to be determined and should be individualized to fit the swimmer, but an article in the Journal of Strength and Conditioning Research was published this past month which analyzed the aerial start phase in elite freestyle swimmers.In the study, the researchers had the opportunity to work with 11 elite sprint male sprinters (average participant was 94.5%, in swimming terms is 49.56 100 meter free).