{{Short description|Swimming stroke}} {{for|the Iranian film with the same name|Drown (2020 film)}} {{Use dmy dates|date=January 2022}} thumb|Butterfly stroke|alt=Butterfly stroke from the front angle, taken as the swimmer is breathing and his arms are halfway through the recovery phase
'''Butterfly''' (shortened to '''fly'''<ref name="The Guardian – 12 August 2013 – I believe I can butterfly">{{cite news|url=https://www.theguardian.com/lifeandstyle/the-swimming-blog/2013/aug/12/butterfly-swimming-stroke-learn|title=I believe I can butterfly|last=Murphy|first=Sam|date=12 August 2013|work=The Guardian|access-date=7 September 2014}}</ref>) is a swimming stroke swum on the front, with both arms moving symmetrically, accompanied by the butterfly kick (also known as the "dolphin kick") along with the movement of the hips and chest.
It is the newest swimming style swum in competition, first swum in the early 1950s and originating from breaststroke.
For most competitive swimmers, butterfly is the second fastest stroke, slower only than front crawl.{{Sfn|Maglischo|2003|pp=95, 145}}
== Technique == thumb|Swimmer performing the butterfly stroke, filmed from above
alt=Refer to caption|thumb|Animation of the butterfly stroke from the top perspective
thumb|Swimmer performing the butterfly stroke, filmed from underwater
alt=Refer to caption|thumb|Animation of the butterfly stroke from the front perspective
Butterfly is a symmetric and undulating stroke.{{Sfn|Sanders|McCabe|2015|p=87}} The arms move symmetrically down the front of the body and then over the water, and the legs move up and down together in a dolphin kick.{{Sfn|Maglischo|2003|pp=145–147}}{{Sfn|Sanders|McCabe|2015|p=87}} The midline of the body coordinates to form a wave-like motion from head to toe, which establishes a rhythm that the arms coordinate with.{{Sfn|Sanders|McCabe|2015|pp=87–88}} Competitive swimmers often train the butterfly stroke using interval sets that combine short sprint distances with longer aerobic repetitions in order to maintain stroke efficiency under fatigue.{{Citation needed|date=March 2026}}
Each butterfly stroke cycle consists of two kicks and one full arm stroke, with each stroke cycle beginning when the arms enter the water in front.{{Sfn|Maglischo|2003|p=146}}{{Sfn|Seifert|Boulesteix|p=103|Chollet|Vilas-Boas|2008}} Each butterfly leg kick can be broken down into two phases: the upbeat and the downbeat. The upbeat occurs as the legs move upwards, and the downbeat occurs as they move downwards.{{Sfn|Maglischo|2003|p=154}}{{Sfn|Seifert|Boulesteix|p=103|Chollet|Vilas-Boas|2008}} The butterfly arm movement can be broken down into five phases: the entry and stretch, the outsweep and catch, the insweep, the upsweep, and the release and recovery.{{Sfn|Maglischo|2003|p=153}}{{Sfn|Sanders|McCabe|2015|pp=89–95}}
Higher-skilled butterfly swimmers travel further per stroke and exhibit greater synchronisation between the arms and legs at various points throughout each stroke cycle.{{Efn|Elite swimmers exhibit greater synchronisation between the beginning of the arm pull and the upbeat of the first kick, and between the beginning of the arm push and the downbeat of the second kick.|group=note}}{{Sfn|Seifert|Boulesteix|p=96|Chollet|Vilas-Boas|2008}} Greater speed variation within each cycle is also associated with less efficiency.<ref>{{Cite journal |last=Barbosa |first=Tiago M. |last2=Keskinen |first2=K. L. |last3=Fernandes |first3=R. |last4=Colaço |first4=P. |last5=Lima |first5=A. B. |last6=Vilas-Boas |first6=J. P. |date=2005-03-01 |title=Energy cost and intracyclic variation of the velocity of the centre of mass in butterfly stroke |url=https://doi.org/10.1007/s00421-004-1251-x |journal=European Journal of Applied Physiology |language=en |volume=93 |issue=5 |pages=519–523 |doi=10.1007/s00421-004-1251-x |issn=1439-6327|url-access=subscription }}</ref>
=== Entry and stretch === thumb|Butterfly stroke, shortly before the arms enter the water again at the end of the recovery|alt=Butterfly stroke, shortly before the arms enter the water at the end of the recovery; view from behind The entry and stretch begins when the arms enter the water above the head. The arms should enter straight or with the elbows slightly bent, about shoulder-width apart, and with the thumbs pointing downward so that the hands can slice into the water.{{Sfn|Maglischo|2003|pp=155, 156}}{{Sfn|Sanders|McCabe|2015|p=90}} The downbeat of the first kick should occur around the same time as the arms enter the water.{{Efn|In "Swimming Fastest", Ernest Maglischo writes that it should begin slightly before the arm entry.{{Sfn|Maglischo|2003|p=163}} In "Science of Swimming", Ross Sanders and Carla McCabe write that it should assist the arm entry,{{Sfn|Sanders|McCabe|2015|p=90}} and in the Human Movement Science journal, Seifert et al. writes that it should happen slightly after the arm entry.{{Sfn|Seifert|Boulesteix|Chollet|Vilas-Boas|2008|pp=103, 108}}|group=note}}
This leg downbeat occurs at the end of a wave like motion initiated by the upper body travelling downward at the end of the recovery.{{Sfn|Sanders|McCabe|2015|p=90}} The swimmer faces downwards on entry to minimise the hydrodynamic drag on their head and allow the head to initiate the wave.{{Sfn|Sanders|McCabe|2015|p=91}}{{Sfn|Maglischo|2003|p=155}} Greater smoothness on entry contributes to increased forward acceleration from the kick.{{Sfn|Maglischo|2003|p=155}}
Swimmers may glide for a short period of time in a streamlined position after completing the downbeat of the first kick and before starting the outsweep and catch.{{Sfn|Maglischo|2003|pp=154–157}}{{Sfn|Colwin|2002|p=57}}
=== Outsweep and catch === The purpose of the outsweep is to position the arms in such a way as to maximise the propulsion from the insweep that follows. The catch occurs towards the end of the outsweep and is the position from which the swimmer transitions to the insweep.{{Sfn|Maglischo|2003|p=157}}
During the outsweep, the hands sweep outward and rotate, and the elbows bend, such that by the end of the outsweep, the arms are further than shoulder-width apart and the whole of each arm is facing backwards against the water. Throughout the outsweep, the arms decelerate so that they are moving slowly during the catch before accelerating during the insweep.{{Sfn|Maglischo|2003|p=157}}
The movement of the outsweep, the upbeat of the second kick, and the buoyancy force from the upper body all work to cause the upper body to begin to rise.{{Sfn|Sanders|McCabe|2015|p=92}} During this phase, the head also begins to lift.{{Sfn|Maglischo|2003|p=157}}
=== Insweep === The insweep begins when the water is caught at the end out the outsweep. The arms accelerate in a semi-circle towards the waist, moving slightly outwards at the beginning of the insweep and then inwards for the remainder of the phase. The insweep finishes when the hands are close together near the middle of the body.{{Sfn|Maglischo|2003|p=157}} Moving the arms in this shape allows them to pull more still water, which provides greater resistance and therefore greater propulsion. It also makes the pull longer, allows multiple muscles to assist with the pull, and transitions well into the upsweep.{{Sfn|Sanders|McCabe|2015|p=94}}
During the insweep, the whole of each arm is used to pull back on the water and generate propulsion,{{Sfn|Maglischo|2003|p=157}} with the elbows being held high and bent to almost right angles to provide leverage against the water.{{Sfn|Colwin|2002|pp=56, 58}}{{Sfn|Maglischo|2003|p=157}} The insweep movement of each arm is similar to the insweep motion in front crawl, however in contrast to in front crawl, the butterfly arms move together so their torques cancel out and there is no rotation along the body's longitudinal axis.{{Sfn|Sanders|McCabe|2015|pp=93–94}}
During the insweep, the upper body and head continue to rise and the legs prepare to initiate the downbeat of the second kick.{{Sfn|Sanders|McCabe|2015|pp=93–94}} At the end of the insweep, as the arms transition into the upsweep, the head should exit the water.{{Sfn|Maglischo|2003|p=168}}
=== Upsweep === The upsweep is initiated by the hands altering their backwards trajectory to move away from each other and upwards towards the surface of the water. The elbows remain bent, so the arm can continue to pull back on the water, and, after decelerating during the transition from the insweep, the arms accelerate again to provide propulsion. The upsweep finishes as the hands decelerate for the last time underwater, preparing to exit the water for the recovery. By this point, the hands should be near the thighs.{{Sfn|Maglischo|2003|p=159}}
=== Release and recovery === The deceleration of the arms causes them to release pressure on the water and cease providing propulsion. The hands then turn so that the palms face inward, which allows the hands to exit the water with minimal drag. The upper arms then exit the water first, followed by the lower arms and hands. As the arms exit the water, the elbow straightens, so that during the rest of the recovery, the arms are either fully extended or almost fully extended. The arms then travel out and over the surface of the water, so that they are ready to enter thumbs first and begin the next stroke cycle. The muscles in the arms should be relaxed as much as possible during the recovery, to allow them to recover ready for the next cycle.{{Sfn|Maglischo|2003|pp=159–160}}
If the swimmer sharply decelerates the arms during the release, at the body's peak velocity during the upsweep, then the swimmers velocity will sharply decrease. If this occurs, then the wake of the wave generated by the swimmer when they were at peak velocity will catch up during the first half of the recovery and propel them forward. This phenomenon is termed ''wave propulsion''.{{Sfn|Maglischo|2003|p=161}}
== Start, turn and finish == {{More citations needed|section|date=April 2020}} Butterfly uses the regular start for swimming, if in a competition the swimmer would start off a diving block. After the start, a gliding phase follows underwater, followed by dolphin kicks swimming underwater. Swimming underwater reduces the drag from breaking the surface and is very economical. Rules allow for 15 m underwater swimming before the head breaks the surface and regular swimming begins.
The turn and finish requires the swimmer to touch the wall "with both hands separated and simultaneously".<ref name=":0">{{Cite web |date=1 January 2023 |title=FINA Swimming Rules |url=https://resources.fina.org/fina/document/2023/01/04/65961a45-bde5-4217-b666-ca1f5dc2d1f0/1_Swimming-Technical-Rules.04.01.2023.pdf |url-status=live |archive-url=https://web.archive.org/web/20231209220352/https://resources.fina.org/fina/document/2023/01/04/65961a45-bde5-4217-b666-ca1f5dc2d1f0/1_Swimming-Technical-Rules.04.01.2023.pdf |archive-date=9 December 2023 |access-date=9 December 2023 |website=FINA}}</ref> Both hands must simultaneously touch the wall during turns and finish while the swimmer remains swimming face down. The swimmer touches the wall with both hands while bending the elbows slightly. The bent elbows allow the swimmer to push themself away from the wall and turn sideways. One hand leaves the wall to be moved to the front underwater. At the same time, the legs are pulled closer and moved underneath the body towards the wall. The second hand leaves the wall to be moved to the front over water. It is commonly referred to as an "over/under turn" or an "open turn". The legs touch the wall, and the hands are at the front. The swimmer sinks underwater and lies on the breast, or nearly so. Then the swimmer pushes off the wall, keeping a streamlined position with the hands to the front. Like the start, the swimmer is allowed to swim 15 metres underwater before the head breaks the surface. Most swimmers dolphin kick after an initial gliding phase.
== History ==
=== Origins of the butterfly kick === The International Swimming Hall of Fame attributed the earliest mention of the butterfly kick to George Corsan, who introduced it by demonstration to David Armbruster in 1911, calling it the "fishtail kick".{{Efn|In The Making of the Atomic Bomb, physicist Volney Wilson is credited with inventing the kick after analyzing the movements of fish.<ref>{{Cite book |last=Rhodes |first=Richard |title=The Making of the Atomic Bomb |publisher=Penguin Books |year=1988 |isbn=0140116672 |edition= |pages=422 |language=en}}</ref>|group=note}}<ref>{{Cite web |title=Dave Armbruster - ISHOF |url=https://ishof.org/honoree/honoree-dave-armbruster/ |url-status=live |archive-url=https://web.archive.org/web/20231212104510/https://ishof.org/honoree/honoree-dave-armbruster/ |archive-date=12 December 2023 |access-date=12 December 2023 |website=International Swimming Hall of Fame}}</ref> Another discovery of the butterfly kick was made by Jack Sieg, who, while being watched by Armbruster, went underwater, lay on his side, and performed the butterfly kick in imitation of a fish.{{Sfn|Maglischo|2003|p=145}}{{Sfn|Barney|Barney|2008|p=19}}<ref name=":1">{{Cite journal |last=Armbruster |first=David |date=1935 |title=The Dolphin Breast Stroke |url=https://www.tandfonline.com/doi/abs/10.1080/23267240.1935.10620880 |journal=The Journal of Health and Physical Education |volume=6 |issue=4 |doi=10.1080/23267240.1935.10620880 |via=Taylor & Francis Online|url-access=subscription |page=24}}</ref> Sieg and Armbruster further experimented with the kick until Sieg was able to beat the best flutter kickers at the University of Iowa using it.<ref name=":1" />
Armbruster and Sieg experimented with using the butterfly kick in breaststroke and had excellent results. Presumably to reflect this, he also began referring to the previously named "fishtail kick" as the "dolphin breaststroke kick".{{Sfn|Barney|Barney|2008|p=20}} He published his results in 1935 in an article called "The Dolphin Breast Stroke" in ''The Journal of Health and Physical Education''<ref name=":1" /> where, due to its potential to be faster than the traditional whip kick, Armbruster was enthusiastic to have it legalized within the breaststroke rules, to "offer this new type of stroke for exploitation as a competitive racing-speed stroke".<ref name=":1" /> Armbruster followed this appeal with another longer article in the 1937 NCAA Swimming and Diving Guide called "The New Dolphin Breast Stroke on Trial", which further urged the NCAA to allow the kick in the rules for the extra speed.<ref>{{Cite book |last=Armbruster |first=David |title=1937 NCAA Swimming and Diving Guide |publisher=American Publishing Company |year=1937 |location=New York |pages=52–57 |language=En}}</ref> Unfortunately for Armbruster, this would not come to fruition, as in a FINA meeting in October 1938, the bureau unanimously agreed to prohibit up-and-down movements of the legs in the vertical plane.<ref name="FINA 1938 p 13">FINA (Federation Internationale de Natation Amateur) Bureau Bulletin, 4 (October 1938), p 13.</ref>
=== Origins of the butterfly arm === Prior to 1935, the breaststroke rules from both FINA and the NCAA stated that the arms had to be simultaneously pushed forward on recovery.{{Sfn|Barney|Barney|2008|p=13}} Since the rules did not state that the arm recovery had to be underwater, a few swimmers came up with the idea of an overarm recovery, which was initially called the "flying fish".<ref>{{Cite book |last=Matt Mann II |first=Charles C. Fries |url=http://archive.org/details/swimming0000matt |title=Swimming |date=1940 |others=Internet Archive}}</ref> The International Swimming Hall of Fame credits Sydney Cavill with creating the overarm recovery,<ref>{{Cite web |title=The Cavill Family |url=https://ishof.org/honoree/honoree-the-cavill-family/ |access-date=2023-12-12 |website=ISHOF |language=en-US}}</ref> but it is also possible that Erich Rademacher independently discovered it in 1927 Germany. Rademacher generally used the flying fish coming out of the turns,<ref name="Erich Rademacher">{{Cite web |title=Erich Rademacher |url=https://ishof.org/honoree/honoree-erich-rademacher/ |access-date=2023-12-12 |website=ISHOF |language=en-US}}</ref> which was dubbed the "flying breaststroke turn" and at the end of the race, which was dubbed the "flying finish".{{Sfn|Colwin|2002|pp=30–31}}
Rademacher insisted that this did not break the rules, and continued to use it in the late 1920s and early 1930s in the US.{{Sfn|Barney|Barney|2008|p=14}} Sources conflict as to whether he used it in the 1928 Olympics, with the International Swimming Hall of Fame saying he did<ref name="Erich Rademacher" /> but Francois Oppenheim's book "The History of Swimming" saying he didn't.<ref>Francois Oppenheim, The History of Swimming, translated from the French by Swimming World Books (New York: Swimming World Books, 1970), p. 120.</ref> In 1935, presumably for the removal of ambiguity, the NCAA changed the rule regarding the breaststroke recovery to use the word "moved", rather than "pushed".<ref>1935 NCAA Swimming and Diving Guide (New York: American Sports Publishing Company, 1935), p. 12.</ref> Other early adoptees of the "flying breaststroke turn" were Walter Spence and then Wallace Spence, who went on to dominate the breaststroke events using it.{{Sfn|Barney|Barney|2008|pp=14–15}} The next notable swimmer to further innovate on the butterfly arms was Henry Myers, who in early December 1933 used the flying fish for the whole of the breaststroke leg of a three-stroke medley head, winning against Wallace Spence in spectacular fashion.{{Sfn|Barney|Barney|2008|p=15}} The reaction to this performance was mixed. Though the officials did not disqualify him, the Brooklyn Central YMCA's magazine wrote a "vitriolic article" that made disparaging remarks about "the sportsmanship of young Myers who observed the letter but not the spirit of the breaststroke rules".<ref>{{Cite news |last=Thierry |first=Nick |year=1997 |title=Swim News - April 1997 (No.227) |work=Swim News |url=https://archive.org/stream/swimnewsn227/swimnewsn227_djvu.txt |access-date=12 December 2023}}</ref> Furthermore, Wallace Spence withdrew from the finals of the event alleging that Myers was swimming freestyle and he should "learn how to swim breaststroke properly".<ref name=":3">Henry Myers to Mr. [Robert] Kiputh, 13 October 1940; published in Robert J. H. Kiphuth, Swimming (New York: The Ronald Press Company, 1942), pp. 80-82</ref> Despite this, Myers was very proud of his creation, saying: "It [is] uninteresting to watch a breaststroke race, in time, the old breaststroke would have become as passe as the English sidestroke, as far as racing is concerned. A butterfly-breaststroke race is a very exciting race to watch. The splashing and violent arm-motion seems to be quite conducive to spectator enthusiasm."<ref name=":3" /> Myers interested two teammates of his: Lester Kaplan and Paul Friesel, in the overarm recovery. Kaplan and Friesel went on to set new personal bests in breaststroke by over 3 seconds using it.<ref name=":3" />
As the overarm recovery caught on more, a swimmer called John Herbert Higgins, in February 1936 at the 1936 National AAU Indoor Swimming Championships swam a time of 1:10.8 for the 100 metre breaststroke event, and became the first swimmer to set a world record using exclusively the flying fish.{{Sfn|Barney|Barney|2008|p=16}} This technique of continuous flying fish would come to be known as "butterfly-breaststroke". Later at the 1936 US Olympic Trials, Higgins set a new 200 metre American Record of 2:44.1.<ref>{{Cite web |title=1936 US Olympic Team Trials |url=https://www.usaswimming.org/docs/default-source/eventsdocuments/meet-results/olympic-trials-results/1936-us-olympic-team-trials.pdf |url-status=live |archive-url=https://web.archive.org/web/20231212120942/https://www.usaswimming.org/docs/default-source/eventsdocuments/meet-results/olympic-trials-results/1936-us-olympic-team-trials.pdf |archive-date=12 December 2023 |access-date=12 December 2023 |website=USA Swimming}}</ref> In the 1936 Berlin Olympic 200m breaststroke finals, Higgins finished fourth while using the butterfly-breaststroke technique.<ref>{{Cite web |title=Olympedia – 200 metres Breaststroke, Men |url=https://www.olympedia.org/results/5070 |access-date=2023-12-12 |website=www.olympedia.org}}</ref><ref>{{Citation |title=1936 Olympic 200 breaststroke | date=13 March 2012 |url=https://www.youtube.com/watch?v=l-R4wiSZcRc |access-date=2023-12-12 |language=en}}</ref> Though the butterfly-breaststroke was gaining traction, it was almost prohibited as a style of breaststroke in an October 1938 FINA Executive Bureau meeting where it was "supported by four votes out of seven to prohibit the butterfly arm recovery in the breaststroke event. However, since alterations to the technical rules required a two-thirds majority before adoption, the motion was declared not carried".<ref name="FINA 1938 p 13" /> In the 1948 London Olympics, all but one of the finalists used the butterfly-breaststroke technique, and the only finalist who did not use it (Bob Bonte of the Netherlands) finished last.<ref>{{Cite web |title=Olympedia – 200 metres Breaststroke, Men |url=https://www.olympedia.org/results/5181 |access-date=2023-12-12 |website=www.olympedia.org}}</ref>
This dominant display of butterfly-breaststroke led to the idea of separating breaststroke into two breaststroke events, consisting of traditional breaststroke and butterfly-breaststroke.<ref>Max Ritter to Bert Sollfors, 6 March 1949, ISHOF, Fort Lauderdale, Florida, USA</ref> However, the IOC president Sigfrid Edstrom decided not to add any events to the 1952 Helsinki Olympics, due to the chaotic situation after World War II.{{Sfn|Barney|Barney|2008|pp=21–22}} Despite this, FINA did add a definition of the two styles of breaststroke to the rules which named traditional breaststroke style "A" and butterfly-breaststroke style "B". A consequence of this was competitors were not able to swim both of the styles in the same race.<ref>FINA Bureau Bulletin, No. 9, January 1949, pp. 21-22</ref>
=== Origins of the full butterfly stroke === By 1952, the argument for separating the "A" and "B" styles of breaststroke was gaining momentum,<ref>FINA Bureau Bulletin, April 1952.</ref> and hence in 1953, breaststroke was separated into two different events. Furthermore, while traditional breaststroke required the whip kick, the new butterfly stroke allowed the use of butterfly kick. Now the butterfly stroke was its own separate event.<ref>1953-1956 FINA Rules Book, p. 29.</ref> The butterfly stroke was first seen in the Olympics at the 1956 games, where the Men's 200 metre butterfly event was won by William Yorzyk, and the Women's 100 metre Butterfly event was won by Shelley Mann.<ref>{{Cite web |date=13 December 2023 |title=Olympedia – 200 metres Butterfly, Men |url=https://www.olympedia.org/results/5421 |url-status=live |archive-url=https://web.archive.org/web/20231213074917/https://www.olympedia.org/results/5421 |archive-date=13 December 2023 |access-date=13 December 2023 |website=Olympedia}}</ref>
== Olympic and world long-course champions in butterfly ==
=== Men === {{Footer Olympic Champions 100 m Butterfly Men}} {{Footer Olympic Champions 200 m Butterfly Men}} {{Footer World LC Champions 50m Butterfly Men}} {{Footer World LC Champions 100m Butterfly Men}} {{Footer World LC Champions 200m Butterfly Men}}
=== Women === {{Footer Olympic Champions 100 m Butterfly Women}} {{Footer Olympic Champions 200 m Butterfly Women}} {{Footer World LC Champions 50m Butterfly Women}} {{Footer World LC Champions 100m Butterfly Women}} {{Footer World LC Champions 200m Butterfly Women}}
== Notes == {{Notelist|group=note}}
== References == {{Reflist}}
== Bibliography == * {{Cite book |last=Maglischo |first=Ernest |url=https://archive.org/details/swimmingfastest0000magl/ |title=Swimming Fastest |publisher=Human Kinetics |year=2003 |isbn=0736031804 |edition=3rd |location=Champaign, Illinois |pages= |language=En}} * {{Cite journal |last=Seifert |first=L. |last2=Boulesteix |first2=L. |last3=Chollet |first3=D. |last4=Vilas-Boas |first4=J. P. |date=2008-02-01 |title=Differences in spatial-temporal parameters and arm–leg coordination in butterfly stroke as a function of race pace, skill and gender |url=https://www.sciencedirect.com/science/article/pii/S0167945707000735 |journal=Human Movement Science |volume=27 |issue=1 |page= |pages= |doi=10.1016/j.humov.2007.08.001 |issn=0167-9457 |via=ScienceDirect|url-access=subscription }} * {{Cite journal |last=Barney |first=David |last2=Barney |first2=Robert |date=December 2008 |title=A Long Night's Journey Into Day: the Odyssey of Butterfly |url=https://library.olympics.com/FIBA/doc/SYRACUSE/2876227/a-long-night-s-journey-into-day-the-odyssey-of-butterfly-david-e-barney-robert-k-barney?_lg=en-GB |journal=Journal of Olympic History |volume=16 |issue=3 |pages=11–25 |via=Olympic World Library}} * {{Cite book |last=Sanders |first=Ross |title=Science of Swimming Faster |last2=McCabe |first2=Carla |publisher=Human Kinetics |year=2015 |isbn=978-0-7360-9571-6 |editor-last=Riewald |editor-first=Scott |language=en |editor-last2=Rodeo |editor-first2=Scott}} * {{Cite book |last=Colwin |first=Cecil |title=Breakthrough Swimming |date=2002-02-20 |publisher=Human Kinetics |isbn=9780736037778}}
== External links == * {{Commons category-inline|Butterfly (swimming style)}}
{{Swimming styles}} {{Authority control}}
Category:Butterfly stroke Category:Swimming styles