THE EFFECT of WEARING a CAP on the SWIMMER PASSIVE DRAG Power

Vilas-Boas, Machado, Kim, Veloso (eds.) Portuguese Journal of Sport Sciences Biomechanics in Sports 29 11 (Suppl. 2), 2011 and Padullés, 2000). It is also a good indicator of the predominance of alactic anaerobic THE EFFECT OF WEARING A CAP ON THE SWIMMER PASSIVE DRAG power. The average results of the 5” Rebound Jump for Robles and Quiñónez were, respectively: contact time (s): 168 ± 8 and 178 ± 5, heigth (cm): 37,6 ± 3,2 and 26,9 ± 2,3, 1,2 2,3 2,3 -1 Daniel A. Marinho , Vishveshwar R. Mantha , Abel I. Rouboa , João P. Vilas- mechanics power (W/kg): 57,27 ± 4,71 and 41,15 ± 2,65, speed of takeoff (m·s ): 2,71 ± Boas4,5, Leandro Machado4,5, Tiago M. Barbosa2,6 and António J. Silva2,3 0,11 and 2,29 ± 0,10. And the average results of the 15” Rebound Jump for Robles and

Quiñónez were, respectively: contact time (s): 182 ± 7 and 180 ± 6, heigth (cm): 41,8 ± 3,1 Department of Sport Sciences, University of Beira Interior, Covilhã, Portugal1 and 28,4 ± 2,8, mechanics power (W/kg): 59,32 ± 4,65 and 42,60 ± 3,61, speed of takeoff 2 (m·s-1): 2,85 ± 0,11 and 2,35 ± 0,12. These differences clearly indicate a greater reactive Research Centre in Sport, Health and Human Development, Portugal strength in Robles, which is also related to the results of the contact time in races. Department of Sport Sciences, University of Trás-os-Montes and Alto Douro, 3 Vila Real, Portugal 4 CONCLUSION: The race analysis tests and strength assessment of the two athletes in the Faculty of Sport/CIFI2D, University of Porto, Porto, Portugal sample showed that Dayron Robles is faster than Quiñónez in that he has shorter contact Porto Biomechanics Laboratory (LABIOMEP), University of Porto, Porto, time on the race supports, greater reactive strength and the ability to reach the first hurdle in Portugal5 seven strides. This study proposed that Robles could improve his performance by reducing Department of Sport Sciences, Polytechnic Institute of Bragança, Bragança, the flight time in the hurdle clearance. The direct transfer of the results of this research to Portugal6 Robles' coach produced technical improvements in the athlete, which were materialised in the IAAF World Indoor Championships in Doha 2010, at which Robles was victorious. The purpose of this study was to analyse the effect of wearing a cap on swimmer passive drag. A computational fluid dynamics analysis was carried-out to determine the REFERENCES: hydrodynamic drag of a female swimmer’s model: (i) wearing a swimming cap and; (ii) Antúnez, S. (2009) Hurdles. 1st IAAF Coaches Conference. Kienbaum (Germany) with no cap. The three-dimensional surface geometry of a female swimmer’s model with cap and with no cap was acquired through standard commercial laser scanner. Passive Bosco, C. (1997) La forza muscolare. Roma: Società Stampa Sportiva. drag force and drag coefficient were computed with the swimmer in a streamlined Brüggemann, G.-P., Koszewski, D. & Müller, H. (1999) Biomechanical Research Project position. Higher hydrodynamic drag values were determined when the swimmer was with Athens 1997 Final Report. Oxford: Meyer & Meyer Sport. no cap in comparison with the situation when the swimmer was wearing a cap. In Kuitunen; S. (2010) Biomechanical analysis men 60 m hurdles final. Doha: ASPIRE. conclusion, one can state that wearing a swim cap may positively influence swimmer’s hydrodynamics. López, J.L. & Padullés, J.M. (2000) La tecnología MuscleLab: de la Agencia Norteamericana del Espacio (NASA) al deporte. Barcelona: Fundació Barcelona Olímpica. KEY WORDS: CFD, swimming, model, sports equipment. Schmolinsky, G. (2000) Track and Field. Toronto: Sports Books. INTRODUCTION: Swimming velocity depends on the interaction between hydrodynamic drag force and propelling force. Aiming to achieve higher velocities the swimmer should minimize the hydrodynamic drag force resisting forward motion and maximize the propelling force. Regarding the first aim, several studies analyse the effect of wearing different equipments on hydrodynamic drag, with special attention to the use of swimsuits (e.g., Mollendorf et al., 2004; Pendergast et al., 2006; Toussaint et al., 2002). Regarding the benefits of wearing the new generation of swimsuits, it seems their use allows to mold the swimmer’s body into a more streamlined shape, reducing the hydrodynamic profile and minimizing oscillations/vibrations in muscles and other body wobbling masses that might disturb the flow (Marinho et al., 2009). Nevertheless, the research regarding the effect of wearing a swim cap on hydrodynamic drag is not reported, although its use is almost consensual on reducing changes on the body shape of the head, especially on female swimmers with long hairs. Therefore, the purpose of this study was to analyse the effect of wearing a cap on a female swimmer passive drag.

METHODS: The numerical simulation of the fluid flow around the two swimmer’s models was carried out in Ansys FluentTM 6.3 commercial software (Ansys, Canonsburg, Pennsylvania, U.S.A.). The simulations are based on Finite volume method of discretization. The three- dimensional surface geometry model was acquired through standard commercial laser scanner Vitus Smart XXL 3D body scanner (Human Solutions Company, Kaiserslautern, Germany), as used previously (Bixler et al., 2007; Leong et al., 2007). The subject of this study was an Olympic level female swimmer (height 1.66m, weight 55.0kg, age 23 years- old). The swimmer was fully informed of the aims of the participation in the investigation and voluntarily agreed in participation, with the signing of written informed consent. The swimmer was in rest along the body scans. Each scan took an average of 20 minutes. Care was taken to limit differences in alignment of the individual scans for the two situations, by fixing the

ISBS 2011 319 Porto, Portugal Vilas-Boas, Machado, Kim, Veloso (eds.) Portuguese Journal of Sport Sciences Biomechanics in Sports 29 11 (Suppl. 2), 2011 position of feet, maintaining similar vertical and horizontal alignment in respective scans and also the stationary pose with control of breadth (Lashawnda & Cynthia, 2002) during the actual moment of acquiring the scan. The swimmer presented her arms extended above the 0.45 head (shoulders flexed), with one hand above the other (streamlined position). The three- dimensional geometric models were used later for analysis through computational fluid 0.40 dynamics simulation. 0.35 The quadrilateral computational domain of 20m length, 2.5m breadth and 1.5m height with 0.30 inlet at 5m upstream of the swimmer model was prepared in GambitTM preprocessor (Ansys, Canonsburg, Pennsylvania, U.S.A.). The computational domain consisted of about 11 0.25 thousand tetrahedral grid cells. The passive drag was determined with the swimmer model at

Drag coefficient Drag 0.20 With cap a depth of 0.75m. Drag force and drag coefficient were computed for flow velocities of 1.5, 2.0 and 2.5m/s. 0.15 With no cap 0.10 Figures 1 and 2 present the values of drag force and drag coefficient for the RESULTS: 0.05 female swimmer’s model in the two analysed situations, wearing a cap and with no cap, 0.00 respectively. As one can observe, the situation when the swimmer is with no cap presented Flow velocity (m/s) higher hydrodynamic drag values than the situation when the swimmer is wearing a cap. For 1.5 2.0 2.5 instance, for a flow velocity of 2.0m/s the decrease of drag force and drag coefficient when Figure 2: Values of drag coefficient for the female swimmer’s model with cap and with no cap. the swimmer is wearing a cap is about 17% and 13%, respectively, comparing with the situation when the swimmer is gliding without a swim cap. Regarding the drag coefficient values, one can note that there was an inverse relationship Moreover, one can verify that drag force increases with flow velocity and the opposition between this variable and the velocity flow. The drag coefficient decreased as velocity situation occurs for drag coefficient. increased. This situation was reported previously both on experimental and numerical investigations in swimming (Lyttle et al., 1999; Bixler et al., 2007) for swimmers wearing a DISCUSSION: The purpose of this study was to analyse the effect of wearing a cap on a cap. Moreover, the current results are very similar to the ones presented by Bixler et al. female swimmer passive drag. Numerical simulations were applied to analyse drag force and (2007), using numerical simulations on a three-dimensional model of the human body of an drag coefficient in both situations. The main data has shown that the use of a cap during the elite swimmer (values of about 0.30 for velocities ranging from 1.5 to 2.25m/s). Concerning swimming glide can lead to a ~15% decrease on passive drag. drag force, similar data was also obtained. Lyttle et al. (1999), at the lower velocity studied Computational fluid dynamics methodology is based on computer simulations, allowing to (1.6m/s), and at the deepest studied towing position (0.6m deep), reported values within the test several conditions and to obtain the best result, without physical/experimental testing. range of the current study (58.1N). Bixler et al. (2007) found drag force values of 31.58 and This methodology was developed to be valid and accurate in a large scope of fluid 55.57N for velocities of 1.5 and 2.0m/s, respectively, with the human model at a prone environments, bodies and tasks, including sports, being scientifically assumed to have position with the arms extended at the front. In this position we found drag force values of ecological validity for swimming research (Bixler et al., 2007; Marinho et al., 2010). On the 44.41 and 76.23N (wearing a cap) and of 53.12 and 86.35N (with no cap), for velocities of other hand, reverse engineering procedures were used to obtain accurate digital models of 1.5 and 2.0m/s, respectively. the female swimmer. Several studies have shown the great potential offered by reverse Considering these results, we believe the current numerical simulation allowed to determine engineering procedures for developing true digital models of the human body to improve the the difference on passive drag between to wear or not to wear a swim cap during the gliding. prediction of hydrodynamic forces in swimming (Bixler et al., 2007; Lecrivain et al., 2008). There has been some research on the effects of wearing different swimsuits on hydrodynamic drag (Mollendorf et al., 2004; Pendergast et al., 2006; Toussaint et al., 2002). However, to the best of our knowledge, there is no evidence in the literature of the effects of wearing a swim cap in swimming. The reduction of ~15% on hydrodynamic drag during the 160 gliding reported in this research should be confirmed with other studies, analysing swimmers of different level and different gender, since this study was performed with one single female

140 swimmer. Additionally, some attempts should be carried-out to analyse the effects of wearing 120 different types and shapes of swim caps and hair positions on hydrodynamic drag.

100 CONCLUSION: The results pointed out that there is an advantage of wearing a swim cap on 80 swimming performance. The 15% decrease on hydrodynamic drag underlines the Drag force force Drag (N) With cap importance of the equipment on swimming hydrodynamics. Therefore, swimmers and their 60 With no cap coaches should pay additional care on the selection of the swimming equipment during 40 training and competition.

20 REFERENCES: 0 Bixler, B., Pease, D. & Fairhurst, F (2007). The accuracy of computational fluid dynamics analysis of Flow velocity (m/s) the passive drag of a male swimmer. Sports Biomechanics, 6, 81-98. 1.5 2.0 2.5

Figure 1: Values of drag force for the female swimmer’s model with cap and with no cap.

ISBS 2011 320 Porto, Portugal Vilas-Boas, Machado, Kim, Veloso (eds.) Portuguese Journal of Sport Sciences Biomechanics in Sports 29 11 (Suppl. 2), 2011 position of feet, maintaining similar vertical and horizontal alignment in respective scans and also the stationary pose with control of breadth (Lashawnda & Cynthia, 2002) during the actual moment of acquiring the scan. The swimmer presented her arms extended above the 0.45 head (shoulders flexed), with one hand above the other (streamlined position). The three- dimensional geometric models were used later for analysis through computational fluid 0.40 dynamics simulation. 0.35 The quadrilateral computational domain of 20m length, 2.5m breadth and 1.5m height with 0.30 inlet at 5m upstream of the swimmer model was prepared in GambitTM preprocessor (Ansys, Canonsburg, Pennsylvania, U.S.A.). The computational domain consisted of about 11 0.25 thousand tetrahedral grid cells. The passive drag was determined with the swimmer model at

coefficient Drag 0.20 With cap a depth of 0.75m. Drag force and drag coefficient were computed for flow velocities of 1.5, 2.0 and 2.5m/s. 0.15 With no cap 0.10 Figures 1 and 2 present the values of drag force and drag coefficient for the RESULTS: 0.05 female swimmer’s model in the two analysed situations, wearing a cap and with no cap, 0.00 respectively. As one can observe, the situation when the swimmer is with no cap presented Flow velocity (m/s) higher hydrodynamic drag values than the situation when the swimmer is wearing a cap. For 1.5 2.0 2.5 instance, for a flow velocity of 2.0m/s the decrease of drag force and drag coefficient when Figure 2: Values of drag coefficient for the female swimmer’s model with cap and with no cap. the swimmer is wearing a cap is about 17% and 13%, respectively, comparing with the situation when the swimmer is gliding without a swim cap. Regarding the drag coefficient values, one can note that there was an inverse relationship Moreover, one can verify that drag force increases with flow velocity and the opposition between this variable and the velocity flow. The drag coefficient decreased as velocity situation occurs for drag coefficient. increased. This situation was reported previously both on experimental and numerical investigations in swimming (Lyttle et al., 1999; Bixler et al., 2007) for swimmers wearing a DISCUSSION: The purpose of this study was to analyse the effect of wearing a cap on a cap. Moreover, the current results are very similar to the ones presented by Bixler et al. female swimmer passive drag. Numerical simulations were applied to analyse drag force and (2007), using numerical simulations on a three-dimensional model of the human body of an drag coefficient in both situations. The main data has shown that the use of a cap during the elite swimmer (values of about 0.30 for velocities ranging from 1.5 to 2.25m/s). Concerning swimming glide can lead to a ~15% decrease on passive drag. drag force, similar data was also obtained. Lyttle et al. (1999), at the lower velocity studied Computational fluid dynamics methodology is based on computer simulations, allowing to (1.6m/s), and at the deepest studied towing position (0.6m deep), reported values within the test several conditions and to obtain the best result, without physical/experimental testing. range of the current study (58.1N). Bixler et al. (2007) found drag force values of 31.58 and This methodology was developed to be valid and accurate in a large scope of fluid 55.57N for velocities of 1.5 and 2.0m/s, respectively, with the human model at a prone environments, bodies and tasks, including sports, being scientifically assumed to have position with the arms extended at the front. In this position we found drag force values of ecological validity for swimming research (Bixler et al., 2007; Marinho et al., 2010). On the 44.41 and 76.23N (wearing a cap) and of 53.12 and 86.35N (with no cap), for velocities of other hand, reverse engineering procedures were used to obtain accurate digital models of 1.5 and 2.0m/s, respectively. the female swimmer. Several studies have shown the great potential offered by reverse Considering these results, we believe the current numerical simulation allowed to determine engineering procedures for developing true digital models of the human body to improve the the difference on passive drag between to wear or not to wear a swim cap during the gliding. prediction of hydrodynamic forces in swimming (Bixler et al., 2007; Lecrivain et al., 2008). There has been some research on the effects of wearing different swimsuits on hydrodynamic drag (Mollendorf et al., 2004; Pendergast et al., 2006; Toussaint et al., 2002). However, to the best of our knowledge, there is no evidence in the literature of the effects of wearing a swim cap in swimming. The reduction of ~15% on hydrodynamic drag during the 160 gliding reported in this research should be confirmed with other studies, analysing swimmers of different level and different gender, since this study was performed with one single female

140 swimmer. Additionally, some attempts should be carried-out to analyse the effects of wearing 120 different types and shapes of swim caps and hair positions on hydrodynamic drag.

Figure 1: Values of drag force for the female swimmer’s model with cap and with no cap.

ISBS 2011 321 Porto, Portugal Vilas-Boas, Machado, Kim, Veloso (eds.) Portuguese Journal of Sport Sciences Biomechanics in Sports 29 11 (Suppl. 2), 2011

Lashawnda, M. & Cynthia, L.I. (2002). Body scanning: effects of subject respiration and foot THE RELATIONSHIP BETWEEN FRONT CRAWL PERFORMANCE AND positioning on the data integrity of scanned measurements. Journal of Fashion Marketing HYDRODYNAMICS IN YOUNG FEMALE SWIMMERS Management, 6, 103-121.

Lecrivain, G., Slaouti, A., Payton, C. & Kennedy, I. (2008). Using reverse engineering and Daniel A. Marinho1,2, Roberto Oliveira1,2, Nuno D. Garrido2,3, Tiago M. computational fluid dynamics to investigate a lower arm amputee swimmer’s performance. Journal of 2,4 2,4 2,3 1,2 Biomechanics, 41, 2855-2859. Barbosa , Mário J. Costa , António J. Silva and Aldo M. Costa Leong, I.F., Fang, J.J. & Tsai, M.J. (2007). Automatic body feature extraction from a marker-less 1 scanned human body. Computer-Aided Design, 39(7), 568-582. Department of Sport Sciences, University of Beira Interior, Covilhã, Portugal 2 Lyttle, A.D., Blanksby, B.A., Elliott, B.C. & Lloyd, D.G. (1999). Optimal depth for streamlined gliding. In Research Centre in Sport, Health and Human Development, Portugal K.L. Keskinen, P.V. Komi & A.P. Hollander (Eds.), Biomechanics and Medicine in Swimming VIII (pp. Department of Sport Sciences, University of Trás-os-Montes and Alto Douro, 165-170). Jyvaskyla: Gummerus Printing. Vila Real, Portugal3 Marinho, D.A., Barbosa, T.M., Kjendlie, P.L., Vilas-Boas, J.P., Alves, F.B., Rouboa, A.I. & Silva, A.J. Department of Sport Sciences, Polytechnic Institute of Bragança, Bragança, (2009). Swimming simulation: a new tool for swimming research and practical applications. In M. Portugal4 Peters (Ed.), Lecture Notes in Computational Science and Engineering – Computational Fluid Dynamics for Sport Simulation (pp. 33-62). Berlin: Springer. The aim of this study was to analyse the relationship between front crawl performance Marinho, D.A., Barbosa, T.M., Reis, V.M., Kjendlie, P.L., Alves, F.B., Vilas-Boas, J.P., Machado, L., and hydrodynamic variables during leg kicking. Sixteen female swimmers (9.2±0.6 years) Silva, A.J. & Rouboa, A.I. (2010). Swimming propulsion forces are enhanced by a small finger spread. participated in this study. The 200m front crawl performance, the 200m front crawl kicking Journal of Applied Biomechanics, 26, 87-92. performance and the active drag during leg kicking were measured. The velocity Mollendorf, J.C., Termin, A.C., Oppenheim, E. & Pendergast, D.R. (2004). Effect of swim suit design perturbation method was used to determine active drag. The 200m front crawl on passive drag. Medicine and Science in Sports and Exercise, 36(6), 1029-1035. performance was significantly correlated with performance in 200m kicking (0.89), with Pendergast, D.R., Mollendorf, J.C., Cuviello, R. & Termin, A.C. (2006). Application of theoretical hydrodynamic drag force during leg kicking (-0.70), and power output in kicking (-0.64). principles to swimsuit drag reduction. Sports Engineering, 9, 65-76. Drag coefficient was not related to the performance in 200 m front crawl. These findings underline the importance of leg kicking to performance in front crawl swimming in these Toussaint, H.M., Truijens, M., Elzinga, M.J., Ven, A. van de, Best, H. & Groot, G. de. (2002). Effect of ages and suggests the important role of kicking tasks during training in young swimmers. a Fast-skin “body” suit on drag during front crawl swimming. Sports Biomechanics, 1(1), 1-10.

KEY WORDS: swimming, children, kicking tasks. Acknowledgement The Portuguese Government supported this work by a grant of the Science and Technology INTRODUCTION: Swimming performance is affected by several factors including swimming Foundation (PTDC/DES/098532/2008; FCOMP-01-0124-FEDER-009569). The authors would like to technique. The swimmer's technical proficiency comprises hydrodynamic variables such as thank the important contribution of the swimmer Sara Oliveira. hydrodynamic drag force and propelling force components. Previous investigations reported that forward propulsion in front crawl swimming is mainly achieved through the arm stroke with minimal contribution from the leg kick (e.g., Hollander et al., 1986; Toussaint & Beek, 1992). Additionally, other authors stated that the leg kick is the most inefficient action of front crawl swimming and its main function is to stabilize the trunk and keep the body in a streamlined position during swimming to reduce hydrodynamic drag (e.g., Bucher, 1974; Laurence, 1969). However, Deschodt et al. (1999) showed that the legs actually improve the propulsive action of the arms, thus improving the generated propulsive force of the whole body. In addition to the controversy around this topic, the investigation under the importance of leg kicking to overall performance in age-group swimmers and in females seems scarce. Therefore, the purpose of this study was to analyse in female age-group swimmers the relationship between front crawl performance and hydrodynamic variables during leg kicking.

METHODS: Sixteen young female swimmers volunteered to participate in this study. Their mean ± 1 standard deviation age, body mass, height and best swimming performance in 200 m front crawl was 9.2±0.6 years-old, 42.4±8.5kg, 1.5±0.1m and, 214.2±48.0s, respectively. All swimmers belonged to the same swimming club and were trained by the same coach for the last two years. The performances in 200m short course front crawl, in the 200m short course front crawl kicking and the active drag during leg kicking were measured in three consecutive days. The velocity perturbation method was used to determine active drag in front crawl kicking (Kolmogorov & Duplishcheva, 1992; Kolmogorov et al., 1997). Active drag was calculated from the difference between the swimming velocities with and without towing the perturbation buoy. To ensure similar maximal power output for the two sprints, the swimmers were instructed to perform maximally at both trials. Both trials were conducted in a 25m indoor swimming pool and in-water starts were used (Marinho et al., 2010). Swimming velocity was assessed during 13m (between 11m and 24m from the starting wall). The time spent to cover

ISBS 2011 322 Porto, Portugal