Getting fast results from the evaluation of swimmers is one of
the most important goals to achieve with technological development
in the field. The purpose of this study was to validate a
real-time velocimetric device (speedometer) through the comparison
of their results with computer assisted videogrametry.
The sample included 7 international level swimmers (3 females
and 4 males). Each swimmer performed four 25m trials, two at
200m race pace and two at 50m race pace. For each trial, two
stroke cycles were studied, resulting on a total of 28 cycles
SWIMMING EVALUATION, ADVICE AND BIOFEEDBACK
Rev Port Cien Desp 6(Supl.2) 201–282 237
analysed. Hip v(t) curves obtained from speedometer and
videogrametry were compared, as well as the speedometer hip
curve with the one of the centre of mass (CM). The higher
mean correlation obtained was between vhip1 and vhip2
(0.955±0.028), followed by vhip1 with vCM (0.920±0.049). The
lower correlation was vhip2 vs. vCM (0.878±0.053). It was concluded
that the speedometer is a reliable, fast and interactive
tool for training advice

Barbosa, Tiago M.

Fernandes, Daniel

Fernandes, R.J.

Gonçalves, P.

Lima, A.B.

Morouço, P.

Semblano, P.

Sousa, F.

Velhote, M.C.

Vilas-Boas, J.P.

Revista Portuguesa de Ciências do Desporto

Getting fast results from the evaluation of swimmers is one of the most important goals to achieve with technological development in the field. The purpose of this study was to validate a real-time velocimetric device (speedometer) through the comparison of their results with computer assisted videogrametry. The sample included 7 international level swimmers (3 females and 4 males). Each swimmer performed four 25m trials, two at 200m race pace and two at 50m race pace. For each trial, two stroke cycles were studied, resulting on a total of 28 cycles analysed. Hip v(t) curves obtained from speedometer and videogrametry were compared, as well as the speedometer hip curve with the one of the centre of mass (CM). The higher mean correlation obtained was between vhip1 and vhip2 (0.955±0.028), followed by vhip1 with vCM (0.920±0.049). The lower correlation was vhip2 vs. vCM (0.878±0.053). It was concluded that the speedometer is a reliable, fast and interactive tool for training advice

J. Paulo Vilas Boas

Miguel V. Correia

Ricardo Fernandes

Antônio B. Lima

Daniel Fernandes

Filipa Sousa

Pedro Gonçalves

Pedro Morouço

Pedro Semblano

Tiago Barbosa

Repositório Aberto da Universidade do Porto

Validation of a cable speedometer for butterfly evaluation

Open Repository of the University of Porto

English

Morouço, Pedro

Lima, António B.

Gonçalves, Pedro

Sousa, Filipa

Fernandes, Ricardo J.

Velhote, Miguel C.

Vilas-Boas, João Paulo

Biblioteca Digital do IPB

Rev Port Cien Desp 6(Supl.2) 201–282236related to development of the terrestrial basis motor patterns(3, 4). Some assessments were performed with electromyogra-phy and video analysis about lower limbs movements of youngchildren (5) and some others about description of leg move-ments of children aged 3-20 months (6). Other authors assertthat water experiences could improve specific skills (2).The aim of this study was to understand if spontaneous swimmovements of the child can evolve into an effective action,after a “keep doing” and a “free exploration” based method-ological approach.METHODSThis study involved 30 children divided into 3 groups (5 malesand 5 females each), aged respectively 4-12 months (group A: age10.8±1.8 months, weight 9.6±1.4 kg, height 74.7±4.44 cm), 12-24 months (group B: age 17.0±2.3 months, weight 11.8±1.7 kg,height 82.8±6.1 cm) and 24-36 months (group C: age 31.9±3.0months, weight 13.7±1.6 kg, height 96.8±7.3 cm). The study was performed with the same teacher, who proposed10 lessons of 30 minutes each. The swimming pool had irregu-lar edge, depth of 90 cm, Cl- 0.6 p.p.m., pH 7-7.4, water tem-perature 33°-34° C, room temperature 29°-30° C. The children experienced the water environment, freely play-ing. Several tools to increase their creativity and their imagina-tion were placed in the water, such as mats, floating toys,slides, balls. No aids to floating, movement or programs toinduce learning to swim were used. The spontaneous behaviours of the children pre and post theperiod of free experience in the water were analyzed. The pres-ence of the following six specific characteristic responses to theaquatic environment stimulation was observed and recorded bypictures and underwater videos: (I) a spontaneous submersion;(II) a balanced body inclination from 20 to 45 degrees; (III) asimultaneous action of the arms, (IV) an alternated action ofthe arms; (V) a simultaneous actions of the legs; (VI) an alter-nated action of the legs. The criterion of scoring employed was: “0” when the character-istic was absent, “1” when it was present. A comparison of the pre-post status within group and a compari-son among the three groups for each characteristic observed, wereconducted with a Mann-Whitney non-parametric Test, for p<0.05.RESULTSNo significant differences (p>0.05) were found in the compari-son between the pre and post experience analysis within group.On the contrary, in the comparison 4-12 versus 24-36 months, asignificant differences (p<0.05) were found in all the character-istics evaluated, except in the spontaneous submersion action.In the comparison 12-24 versus 24-36 months, differences werefound in the body position and in the arm movements (table 1).Table 1.  Comparison among groups with Mann-Whitney Test (* = p<0.05; ** = p<0.01).Characteristics 4-12 Vs. 12-24 12-24 Vs. 24-36 4-12 Vs. 24-36 (months) (months) (months)SubmersionInclined Body Position 20°-45° * *Simultaneous arm movements ** **Alternated arm movements ** **Simultaneous leg  movements *Alternated leg movements **DISCUSSIONFrom the results, it appears that no differences within groupwere noticed in the spontaneous motor actions observed. Wecan suppose that in young children aged 4 to 36 months, a freeexperience in the water environment does not produce effectsin the aquatic motor behaviours considered. On the contrary, variations appear in the comparison amonggroups. In the comparison of the children aged 12-24 versus24-36 months differences were found in the body inclinationand in the arm movements. The children aged 4-12 versus 24-36 months present differences in every aquatic motor behav-iour observed, except in the spontaneous submersion action. Based on the data from the present study, we can suppose that,according to the literature (3), the aquatic motor developmentof the young children should depend mainly on age.REFERENCES1. Erbaugh SJ (1981). The development of swimming skills ofpreschool children over a one and one half year period.Dissertation Abstract International, 42: 2558A.2. Langendorfer S (1987). Children’s movement in the water: adevelopmental and environmental perspective. Children’sEnvironments Quarterl, 4(2): 25-32.3. McGraw MB (1939). Swimming behavior of the humaninfant. J Pediatr, 15: 485-490.4. McGraw MD (1943). The neuromuscular maturation of thehuman infant. New York: Columbia University Press.5. Oka H, Okamoto T, Yoshizawa H, Tokuyama H, KumamotoM (1978). Electromyographic and Cinematographic Study ofthe Flutter Kick in Infants and Children. In: J. Terauds andE.W. Bedingfield (Eds) Swimming III. Baltimore: UniversityPark Press, 167-1726. Wielki C, Houben M (1982). Descriptions of the leg move-ments of infants in an aquatic environment. Biomechanics andMedicine in Swimming. International Series on Sport Sciences,14: 66-71.VALIDATION OF A CABLE SPEEDOMETER FOR BUTTERFLYEVALUATION Pedro Morouço1,2, Antônio B. Lima2,3, Pedro Semblano4,Daniel Fernandes4, Pedro Gonçalves2, Filipa Sousa2,Ricardo Fernandes2, Tiago Barbosa5, Miguel V. Correia4, J.Paulo Vilas-Boas21Management and Technology College, Leiria, Portugal2University of Porto, Faculty of Sport, Porto, Portugal 3Federal University of Ceará, Fortaleza, Brazil4University of Porto, Faculty of Engineering, Porto, Portugal5Department of Sports Sciences, Polytechnic Institute of Bragança,Portugal.Getting fast results from the evaluation of swimmers is one ofthe most important goals to achieve with technological devel-opment in the field. The purpose of this study was to validate areal-time velocimetric device (speedometer) through the com-parison of their results with computer assisted videogrametry.The sample included 7 international level swimmers (3 femalesand 4 males). Each swimmer performed four 25m trials, two at200m race pace and two at 50m race pace. For each trial, twostroke cycles were studied, resulting on a total of 28 cyclesSWIMMING EVALUATION, ADVICE AND BIOFEEDBACKRev Port Cien Desp 6(Supl.2) 201–282 237analysed. Hip v(t) curves obtained from speedometer andvideogrametry were compared, as well as the speedometer hipcurve with the one of the centre of mass (CM). The highermean correlation obtained was between vhip1 and vhip2(0.955±0.028), followed by vhip1 with vCM (0.920±0.049). Thelower correlation was vhip2 vs. vCM (0.878±0.053). It was con-cluded that the speedometer is a reliable, fast and interactivetool for training advice.Key Words: swimming, biomechanics, velocity, speedometer,images processing.INTRODUCTIONSwimming coaches intend to get better competitive results byimproving swimmer’s technique. There are several ways ofdoing so, and biomechanical analysis is, certainly, one of themost accurate and profitable solutions. Nevertheless, biome-chanical analysis normally requires options rather expensiveand time consuming for data analysis. Moreover, in Swimming,the biomechanical evaluation of the stroke technique is limitedby original constraints related with the environment – air andwater -, that do not exist in other sports: (i) the distortions ofthe swimmer’s image produced by the water refraction, undu-lation and turbulence; (ii) the need of obtaining synchronizedimages in two elements of distinct density and (iii) the under-water visibility problems arising due to water aerisation [1].Consequently, in this sport, biomechanical / technical evalua-tion is specially difficult, mainly if we intend to deliver resultsin a fast and useful time for swimmers and coaches. So, gettingfast results from the biomechanical evaluation of swimmers isone of the most important goals to fulfil with technologicaldevelopments related to swimming science. In this domain, one of the most popular and rather informativeevaluation procedures is the assessment of the intra-cyclespeed fluctuation profile of the swimmer. The mean velocity ofa given swimmer depends on the balance between propulsiveand drag forces. During a swimming cycle, the intensities ofboth forces change constantly, once the motor actions are moreor less discontinuous (reaching to his fullness in the simulta-neous techniques), and the relative positions of the body seg-ments are constantly changing [2]. So, in each stroke cycle, thespeed of the swimmer’s forward displacement suffers more orless pronounced modifications due to the positive and negativeaccelerations induced by the continuous variations of theresultant impulses.There are two different ways of measuring the intra-cycle speedprofile of the swimmer: (i) by getting the velocity variations ofan anatomical point (usually the hip) or (ii) analysing theswimmers Centre of Mass (CM) speed profile [3]. A fixedanatomical landmark can be monitored directly using the socold cable Speedometers or Swim-meters, or the propellerbased Swim speed recorders. Radar solutions can also beattempted. Nevertheless, for the CM velocimetry, only imageprocessing solutions can be used, with automatic digitizingroutines seriously compromised due to the dual-media condi-tion. Consequently, this procedures are to much time consum-ing and are characterized by a reduced interaction capacity withthe training process.The purpose of this study was to validate a real-time velocimet-ric device (speedometer) through the comparison of theirresults with those provided for the hip and the CM from com-puter assisted videogrametry. METHODSThe sample included 7 swimmers (63.4±9.3kg; 171.9±12.7cm)from the Portuguese national team, being 3 females and 4 males.As a solution to facilitate images processing, the swimmers weremarked with adhesive tape or ink black colour in the mainanatomical landmarks to be digitalized. Starting in the water,each swimmer performed, two repetitions of 25 meters Butterfly:one at the corresponding velocity of a 200m race (V200m) andother at 50m race pace (V50m). The study included two cyclesin each repetition, resulting on a total of 28 cycles studied. SpeedometerA low cost, house made speedometer was built (fig. 1). Thisinstrument is based over a bobbin set in a tripod using a nylonline with almost no elasticity. This cable is fixed to the swim-mer at the swimming suite, t a middle distance between thetwo hip joints. Fixed to the bobbin, a switch sends a signal to the computer,obtained at a 1000Hz frequency. This data is analysed by thecomputer that gives a graphic v/t in real time (fig. 2). These datacan be exported from the software as ASCII and then be used indifferent analyses with basic software such as Microsoft Excel.Images processingTwo video cameras were used (JVC GR-SX1 SVHS and a JVCGR-SXM 25 SVHS) in a special support with two shelves (fig.3). A camera was 20cm below the water surface, inside awaterproof box (Ikelite Underwater Systems). The other one wasSWIMMING EVALUATION, ADVICE AND BIOFEEDBACKRev Port Cien Desp 6(Supl.2) 201–28223820cm above the water surface. The images obtained in thesagittal plan by the two cameras were synchronized in realtime and mixed in a video mixing table (Panasonic Digital AVMixer WJ-AVE5), originating a dual-media single image withcorrected refraction, that was sent to a video recorder(Panasonic AG-7350 SVHS). The Ariel Performance AnalysisSystem, from Ariel Dynamic Inc., was used with Zatsiorsky modelfor centre of mass kinematical analysis. Into the images obtained were digitized 24 anatomical pointsto get an accurate location of the centre of mass. Lately, resultswere filtered in x and y to eliminate possible errors from digi-talization (Digital Filter Algorithm with a 5Hz frequency). Afterthese procedures all the data were visualized, as shown in pic-ture 4, both with the swimmer video image, the tick figure andthe CM velocity graph. RESULTS AND DISCUSSIONThe variables analysed were vhip1, vhip2 and vCM. The vhip1 standsfor the velocity of the hip obtained by the images processing,vhip2 stands for the velocity of the hip assessed using thespeedometer, and the vCM stands for the velocity of the centreof mass of the swimmer. The kinematics of this last spot wastaken as reference. An example of the v(t) curve for butterflyswimming, taken from one of the subjects of the sample is pre-sented in Figure 5. To obtain this data was necessary to digi-tize, frame by frame, all the anatomical points. This took us alot of time and it is, in fact, a procedure hardly available for theaverage swimming coach. V (m.sec-1)Figure 5. Butterfly intra-cycle velocity variation profiles of vCM from aswimmer during a stroke cycle. Using our home made speedometer we were able to obtain, inreal time, the results presented in Figure 6. There it can beseen the successive cycles performed along the 25m distance,their intra-individual variability, the effect of fatigue associatedwith de decline of the mean velocity, and the intra-cycle varia-tion of velocity (and their kinetics along the test duration). So,immediately after the test, the swimmer and the coach canhave a set of very relevant biomechanical parameters associatedwith the butterfly technique performed just before. In the fig-ure, between the vertical lines, a stroke cycle is defined.Figure 6. Speed profiles of vhip2 from a swimmer during a 25 meterButterfly set.Figure 7.  Velocity profiles obtained for the pooled data for vhip1, vhip2and vCM during a stroke cycle.SWIMMING EVALUATION, ADVICE AND BIOFEEDBACKRev Port Cien Desp 6(Supl.2) 201–282 239The Pearson correlation coefficient computed for each swim-mer between the variables analysed (vhip1, vhip2, and vCM) wasstatistical significant in all cases (p≤ 0,01). The higher meanvalue of the obtained individual r values was found betweenvhip1 and vhip2 (0.955±0.028), followed by vhip1 with vCM(0.920±0.049). The lower mean value for r was obtainedbetween vhip2 vs. vCM (0.878±0.053). After normalizing to thetime duration for the period of a cycle we were able to createthe Figure 6 scattergram and v(t) polynomial fluctuations bestfitted to each distribution (vhip1, vhip2, and vCM).CONCLUSIONSFrom these results we can assume that the study of a swimmerintra-cycle velocity profile assessed through the speedometer isreliable with the profile described for the same anatomicalpoint but obtained through image processing biomechanicalvideogrametry. It is also very strongly correlated with the CMkinematical profile, despite some function discrepancies associ-ated, mainly, to the effect over the CM of the simultaneous for-ward recovery of the arms. So we are strongly convinced thatthis artefact may be of extreme relevance for training evalua-tion and advice, allowing a number of practical applications tothe performance enhancement of swimmers without majorequipments, and time 8and money) costly analysis. REFERENCES[1] Hay, J. (1988). The status of research on the Biomechanicsof Swimming. In: B. Ungerechts, K. Wilke e K. Reischle (eds.)Swimming Science V. Human Kinetics Books, 3-14[2] Nigg, B. M. (1983). Selected methodology in biomechanicswith respect to swimming. In: A. P. Hollander, P. A. Huijing andG. de Groot (eds.) Biomechanics and Medicine in Swimming.Human Kinetics Publishers, 72-80[3] Vilas-Boas, J. P. (1997). Estado actual da investigação sobretécnica desportiva em natação. In: Livro de resumos do 17ºCongresso da Associacion Española de Técnicos de Natácion.Camargo: Cantábria.ESTIMATION THE LAP-TIME OF 200M FREESTYLE FROM AGE ANDTHE EVENT TIMETeruo NomuraKyoto Institute of Technology, Kyoto, Japan.This investigation aimed at the estimation of the lap time of200m freestyle races from age and event time on national levelswimmers. Subjects were 1759 swimmers that selected byD’Agostino-Pearson test of each age from 1857 swimmers thatparticipated in 200m freestyle of the Japanese national levelcompetitions in 2002. The lap time in every 50m and the eventtime were used for analysis. Exponential function approxima-tion of the event time by aging was carried out. Furthermore,the linear regression between a lap time and event time forevery age was calculated respectively. It seems that the compet-itive time of 200m freestyle reach the maturity about 20 yearsold for men and/or 18 years old for women. The estimationformula applied to international level swimmer has high validi-ty (0.904 to 0.987, n=118 and 86) on condition that the agefactor should fix at 22 for over 22 years old male swimmerand/or at 21 for over 21 years old female swimmer.Key words: lap-time, age, event time.INTRODUCTIONThe performance of 200m freestyle improves with aging in theperiod of growth. The contents of race change with grades ofdevelopment of many physical fitness factors. The competitiverecord shows synthetic performance. On the other hand, thelap times are the composition elements of the swimming per-formance. It is not discussed by details about these develop-ment tendencies until now. This investigation aimed at theestimation of the lap time of 200m freestyle races from age andevent time on national level swimmers. This investigationaimed at the estimation of the lap time of 200m freestyle racesfrom age and event time on national level swimmers.METHODSSubjects were 1857 swimmers (men: 935, women: 922) thatparticipated in 200m freestyle of the Japanese national levelcompetitions in 2002. These subjects included from 10 to 22years old. The normal distribution of subjects is required for the para-metric presumption. Therefore, the data arranged in order ofthe event time for every age respectively. The D’Agostino-Pearson test (ZAR 1999) which authorizes the normal distribu-tion from coefficient of skewness and kuytosis was used. Theswimmer which the normal distribution was not held as proba-bility < 0.1 excepted. The lap time in every 50m and the eventtime were used for analysis. It was obtained permission ofthese data use from the Japan Amateur Swimming FederationInformation System Committee. Exponential function approxi-mation of the event time (TIME) by aging (AGE) was carriedout. The time constant (TC) was decided as a correlation ofTIME and a presumed value became the highest. The estima-tion formula of TIME from AGE was as follow: (Eq. 1)Furthermore, the linear regression between a lap time (LAP)and TIME for every age was calculated respectively. The linearregression coefficients were smoothed with 3rd order polyno-mial regression. The estimation formula that calculated theLAP from AGE and TIME was as follow:(Eq. 2)RESULTS AND DISCUSSIONThe 908 men’s and 851 women’s swimmers were selected byD’Agostino-Pearson test applied to the event time. Figure1showed the case of 15 years old boys, 15 slower swimmers werecut from 137 swimmers. The critical point was at 132.75sec.Figure1. Sample selected for the normal distribution by D’Agostino-Pearson test.LAP=(a1AGE3+a2AGE2+a3AGE3+c1)TIME+(b1AGE3+b2AGE2+b3AGE+c2)TIME=a (TIMEmax–TIMEmin)·exp  –(AGE-10)TC+bSWIMMING EVALUATION, ADVICE AND BIOFEEDBACK

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Validation of a cable speedometer for butterfly evaluation

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