52 KINESIOLOGIA SLOVENICA 4 (1 998)1 : 52-54 A COMPARISION BETWEEN FRONT CRAWL AND BUTIERFLY START Boro Štrumbelj Vojko Strojnik Jaka Bednarik Venceslav Kapus PRIMERJAVA MED ŠTARTNIM SKOKOM KRAVL IN DELFIN Abstract The aim o f the present study was to see if a differ- ence in depth of diving between front crawl and but- terfly technique is reflected in corresponding differ- ences in a starting action prior the first contact wi th water. Ten swimmers (age 16.7±1.3 yrs, height 174.2 ±7.2 cm, mass 64.9±7.8 kg) participated in the study. Each swimmer performed 4 (2 crawl and 2 butterfly) grab swimming starts followed by swim- ming w ith maximal velocity for 1 7 meters. Swim- mers were filmed w ith a 50 Hz video camera. A 2 D kinematical model was employed to obtain the joint angles and linear and angular velocities. Statistical differences between both techniques were checked. The results showed that no statistically significant dif- ferences at the starting position and at the first water contact between both styles existed. Duringthe last contact on the starting block, the statistically sign ifi- cant differences appeared only in a knee angle (167.2°±6.2° and 161.4° ±6.7°, P<.05, craw l and butterfly, respectively) and in a knee angular veloci- ty (582 .1 °/s ± 161.1 °/s and 671 °/s ±133.4°/s, P< .05). Obtained resu lts suggest that some differ- ences in a start kinetics were present but had no ef- fect on the flight phase and consecutive diving. Keywords: swimming, grab start, starting action University of Ljubljana - Faculty of Sport, Gortanova 22, 51-1000 Ljubljana, Slovenia phone: ++386 61140-10-77 fax: + + 386 61 448-148 e-mail: 8oro.Strumbelj@sp.uni-lj.si Izvleček Cilj raziskave je bil ugotoviti ali je razlika v globini plavanja pod vodo med kravlovo in delfinovo tehniko posled ica razlike v štartni akciji pred prvim stikom z vodo. V raziskavi je sodelovalo deset plaval- cev (starost 16. 7 ± 1 .3 let, telesna višina 17 4.2 ± 7 .2 cm, telesna masa 64.9±7.8 kg). Vsak plavalec je izvedel 4 (2 kravl in 2 delfin) grab štarte, katerim so sledila maksimalna plavanja do 17 metrov. Plavalci so bili posneti z 50 Hz video kamero. Za ugotavljan- je kotov v sklepih in linearno in kotno hitrost je bil uporabljen 2D kinematični model. Preverjene so bile stati st ične razl ike med obema tehnikama. Rezultati so pokazali, da ni bilo statističnih razlik v štartnem položaju in med prvim stikom z vodo. Pri zadnjem stiku s štartnim blokom so se pokazale statisti čno znači lne razlike samo v kolenskem kotu (167.2°±6.2° in 161.4° ±6.7°, P<.05, kravl oziro- ma delfin) in kotni hitrosti v kolenu (582 .1 °/s ±161.1 °/s in 671°/s ± 133.4°/s, P< .05). Dobljeni rezultati kažejo, da obstojajo določene razlike v štartni akciji, vendar niso imele učinka na fazo leta in plavanje pod vodo. Ključne besede: plavanje, grab štart, štartni skok Boro Štrumbelj, Vojko Strojnik, Jaka Bednarik, Venceslav Kapus A COMPARISION BETWEEN FRONT CRAWLAND BUTTERFLY START lntroduction In swimming, the start plays an important role in fi- nal result, part icularly in the sprint events. The grab start is the most used starting action on the interna- tional competi tions in crawl, butterfl y and breast- stroke. Since Fina rules allowed to the swimmers in butterfly unlimited underwater fly kick, the result is that the butterfly swimmers dive deeper into the wa- ter after the startingaction than the front crawl swim- mers to obtain more efficient propulsion under wa- ter (3) and be consequently faster than on the sur- face. Several studies have been made to compare ef- fectiveness of the grab start to other starting action (1) and to investigate characteristics of the grab start- ing technique (2) . Counsilman et al. compared three startingactions of the grab starts: the scoop start, the fiat start and the track start and fou nd differences in the starting actions as well as in d iving among the startingtechniques (2). The aim of the present study was to see if a differ- ence in depth of diving between both techn iques is reflected in corresponding differences in a starting action prior the first contact w ith water. Methods Four male (age 17.5 ± 1 .3 yrs, height 182.3 ± 7.2 cm, mass 74.5±7.8 kg) and six female (16.2±1 yrs, 168.8±7.4 cm, 58 .6±5.8 kg) swimmers of national and international level from Sloven ia volunteered to participate in the study. Each swimmer performed rhe grab swimming starts fol lowed by swimmingwith maxi mal velocity, either front crawl or butterfly tech- nique for 1 7 meters. Each technique was performed vice. The start w ith a better ti rne at 15 m mark from starting block was analysed. Theswimmingstartwas fi lmed by 50 Hz video cam- era placed perpendicular to the plane of jumping di- rection. The movement from the startingsignal to the ·1rst water contact w ith the hands was analysed by :m kinematical model. The model included 7 body 5egments digitised fro m the right side of the body: ;oot, shank, thigh, trunk, head, upper-arm, and low- er-arm. For the subjects, an acoustic start ing signal ,\as provided, simultaneously a visual marker was displayed for the video camera. The block ti rne was deiined by the frame number from the first visual marker to the last contact of the foot with the block. ::Or the kinematical analysis, the APAS (Ariel O\namics lnc., San Diego, Ca) was used. The fol- 'owing body points were d igit ised: the toe, the lat- eral melleolus, the knee, the hip, the shoulder, the apex, the elbow and the w rist. The centre of gravity (CG) was calculated according to the model from W inter (1990) w hich was modif ied for 20. The co- 53 ordinates of the po ints were smoothed w ith 7 Hz d igita l filter. The joint angles as well as angular ve- locit ies for the ankle, knee, hip and shoulder jo int were calcu lated . These values at the instant of the starti ng signal the end of takeoff and at the first water contact were used for statistical analysis. A takeoff angle of CG and an angle at the water entry were ob- tained. The analysis started w ith a starting signal and ended w ith a fi rst water contact by the hand. Statistical d if- ferences between both styles were tested two-sided w ith the Wilcoxon test for two related samples. Results Table 1 presents comparison between starting posi- tion in frontcrawl and butterfly at the startingsignal . No statistically signi ficant d ifferences between both styles were find neither in joints angle and their an- gular velocities. We can see that the starting position was almostthe sa me in both technique. Table 1.: Starting posit ion at the start ingsignal Crawl Butterflv Joint Angle Ang.veloc Angle Ang.veloc p (') (°' sec-1) (') ('"sec-1) Ankle 97 (8,7) -22,8 (125,7) 96,4 (9,2) 47,8(181,9) n.s. Knee 126,7 (13,6) -33,4 (61,3) 124,9 (11 ,1) 11,1 (106,7) n.s. Hip 24,7(6,1) -58,8(97,1) 22,3 (4,1) -13,0 (48,4) n.s. Shoulder 107,4 (10,3) 6,2 (38,7) 107,5 (9,0) 17,2 (93) n.s. Single celi displays AS and SD (in brackets). • P<0,05 Significant diffe- rence. During the last contact with the start ing block, the statistically significant d ifferences appeared only at the knee angle (167.2°±6.2° and 161.4° ±6.7°, P<.05, crawl and butterfly, respectively) and the knee angular velocity (582.1°/s ± 161.1 °/s and 671°/s ± 133.4°/s, P<0.05)(see Table 2.) . The knee angle at the takeoff was sl ightly smaller in butterfly, but on the other hand a knee angular ve- locity was noticeable higher. Table 2. : Last contact of toes with starting block Crawl Butterflv Joint Angle Ang.veloc Angle Ang.veloc p (') (" sec-1) (') r· sec-1) Ankle 138,7 (9,5) 616,6(116,9) 138,9 (5,9) 568,3 (75,41 n.s. Knee 167,3 (6,2) 582,1 (161,1) 161,4 (6,7)' 671,8 (133,4)" Hip 153,4 (13,6) 535,S (166,4) 147,S (12,1) 551,0(110,2) n.s. Shoulder 110,4 (52,6) -310,8(385,9) 108,5 (53,4) -299,8 (346,7) n.s. CG (x axis) -0,30 (8,09) 2,31 (9,63) n.s. Single celi displays AS and SO (in brackets). • P<0,05 Significant differ- ence. 54 At the first water contact, there were again no statis- t ically significant differences in any of the observed parameters (see Table 3). The med i um entry angle of the body to the water was surprisingly almost the same in both technique. The medi um distance from the starting block was also very similar. Thus the dif- ference obtained at the take off phase was not re- flected at the beginning of water entry. Table 3.: First water contact with hands Crawl Butterfly )oint Angle Ang. veloc Angle Ang. veloc p M ("' sec-1) (") r • sec-1) Ankle 146,5 (11,6) -121,7(183,2) 150,5 (14,5) -24,1 (183,7) n.s. Knee 166,7132,4) 34, 1 (239,4) 164, 1 (40,2) 18,8 (134,3) n.s. Hip 141,811 4,9) 8,2 (228,6) 139,9 (18,8) 12,4 (279,6) n.s. Shoulder 171,816,0) 85,8 (212,4) 170,9 (10,2) 150,9 (166,2) n.s. CG(xaxis) -47,52 (6,62) -48,7819,80) n.s. Distance starting block -wrist 3, 191,22) 3,22 (,26) n.S. Ali values are in degrees except the distance which is in meters. Single celi displays AS and SD (in brackets). • P<0,05 Significant difference. Ali three action phases are shown also in picture 1. Pic. 1 : Analysed starting actions From the pictu re and analysis of the joints angles at the takeoff was also possible to observe that the sub- jects were notextended maximally at the end of take off. The full body extension first occurred after the end of takeoff, during the air-phase. However, this was noticeable for both technique. Discussion Results of this study surprisingly showed that only small differences between starting action in front crawl and butterfly swimming exist. The only observed differences in our study were connected to the knee action at the end of the block contact (see Table 2). However, it was not possible to observe how these d ifferences were compensat- ed byother joints, especially by hips, which regulate the trunk movement since in the later phases at the first contact with the water these differences d isap- peared and also the length of the first water contact Boro Štrumbelj, Vojko Strojnik, Jaka Bednarik, Venceslav Kapus A COMPARISION BETWEEN FRONT CRAWL ANO BUTTERFL Y START was very similar(see Table 3). The takeoff angle be- tween O to 3 degree with tendency to a higher take- off angle in butterfly was find. There are different opinions about an opt imal takeoff angle. Just to make the longest fl ight, the angle should be kept around 40 degrees above the horizontal axis. Horizontal velocity of CG is therefore reduced, but nota resultant velocity. A water entry angle wou ld be in that case greater and more adequately for the butterfly than at more shallow trajectory which is probably more adequate for the crawl. Obtained re- sults suggests that some differences in a manner of a starting impulse production were present but had no effect on the fl ight phase. Since for the swimmers in the butterfly technique a longer diving phase has been observed, we could ex- pect that during the flight phase some differences in the trajectory of the center of gravity wi ll occur, at least in a different entry angle at the first water con- tact, which allows to swimmers to enter deeper into the water. It was found that during scoop start (tech- nique thatallows the bodyto enter atthe same point at w h ich the hands en ter) the angle of entry i nto the water was among 47 degrees what is in accordance with ou r resu lts (2). With this starting action was ob- served the deepest penetration beneath the surface of the water (121 cm) . Since in our study we didn't measure the depth of the penetration, we can only speculate that the entry angle was almost optimal for underwater butterfly kick. It may not be advis- able for the freestyle where the stroke action starts earl ier and should be therefore eliminated. Because of that, the essential d ifferences between styles prob- ably started after the diving into the water. According to the obtained results, it was possible to conclude that some differences in a manner of a starting impu lse production were present but had no effect on the flight phase. References: 1. Bowers JE., Cavanagh PR. A biomechanical comparision of the grab and conventional sprint starts in competitive swim- ming. In: J.P. Clarys and L.Lewillie (eds) Swimming II. lnternational Series on Sport Sciences. Baltimore: University Park Press, 1975: 225-232 2. Counsilman EJ., Counsilman BE., Nomura T., Endo M. Three Types of Grab Starts far Competitive Swimming. National Aquatic Journal; 1988: 4(2): 2-6 3. Whitten P. Should We Limit the Underwater Fly?. Swimming world and junior swimmer; 1997: 38(11 ): 34-36 ACKNOWLEDGEMENTS This study was supported by t he grant from Slovenian ministry for science and technology