Stroke rate and length are two essential players in swimming speed. These two factors play a HUGE role in every stroke, but their impact on swimming velocity is still unknown. Some have gone as far as stating, swimming velocity is the product of stroke length and stroke rate.
In my swim analyses and world record analyses these are the two largest components analyzed, since metabolic cost is able to be tabulated with videos. I argue metabolic cost of stroke rate and stroke length is another factor which is overlooked in swimming research since VO2 testing is not readily available (which embarasses me as a swimmer, but steps are being made http://www.koreaswimming.co.kr/index.php/categories/ksca-document-physiology/146-swimming-vo2-testing ).
It is believed stroke rate and length are on a continuum, as stroke length decreases stroke rate increases, leading to increased velocity. However, there is a fine line between optimal stroke rate and high stroke rate with poor performance (spinning your wheels). This line is a tough cookie to crack since it is different for every swimmer, every stroke and every race.
A recent article looked at the correlation of blood lactate with various stroke rates and lengths during different strokes. This study looked at British national team members who performed a test set of descending 7x200 meters.
The correlation between blood lactate, stroke rate and stroke length were studied. The results indicate as velocity increases stroke rate increases, stroke length decreases and blood lactate increases. Every swimmer could have predicted these results prior to the study, however, research typically comes second to anecdotal evidence, but research concretes and gives reason to philosophies as well as proposing more questions. The researchers noted an inverse correlation with stroke rate and length early during the 7x200, but as velocity increased these differences increased less rapidly. Unfortunately, the participants failed to reach race pace, secondary to fatigue, indicating the results are more practice applicable than race applicable.
However, I would argue these observations can be noted for race conditions and it is noted at every swim meet a swimmer's stroke rate is become too high, their blood lactate increases causing acidity of the blood forcing the swimmer to slow down and under perform. The data in this study could have attempted to correlate blood lactate and VO2max with this test set and I feel would be appropriate in validating as many coaches use this test set to look at anaerobic endurance.
1. Psycharakis S, Cooke C, Paradisis G, O'Hara J, Phillips G. Analysis of selected kinematic and physiological performance determinants during incremental testing in elite swimmers. J Strength Cond Res. May 2008;22(3):951-957.