Biomechanics and Medicine in Swimming XI

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dIscussIon The main aim of this study was to analyze the underwater gliding motion in collegiate competitive swimmers and investigate whether wearing “high speed” swimsuit could maintain the knee and the hip joint angles of 180 degree. The underwater gliding motion of the swimmer is said a significant role in the start and the turn phase. During these phases, reducing underwater resistance force leads to the improvement of the swimming performance. During the underwater gliding motion, the swimmers have to hold a streamlined posture. This posture directly influences the modification of the hydrodynamic resistance created by the swimmer (Havriluk 2007). Elipot et al. (2009) showed that, to hold a streamlined position, a kinematical synergy of the three principal joints’ action is an essential. This synergy is characterized by a combination of the three joints, aiming to stay in the best streamlined position, and to glide longer at high speed. The return to the water surface should rather be initialized by a progressive and synchronize action of the three joints (Elipot et al. 2009). The result of this study showed that the highest speed was maintained during the gliding motion when the knee and the hip joint angles of 180 degrees were maintained from the start to 0.8sec (Figure 7). In addition, swimming speed slowed down when the involuntary movements of flexion-extension in the knee and the hip joints were observed during the gliding motion. These results suggested that the subjects could not maintain the knee and the hip joint angles of 180 degrees during the gliding motion, as the results, might try to maintain the body balance by the flexion-extension movements in the knee and the hip joints. Moreover, high-speed swimsuit would support maintaining the knee and the hip joint angles of 180 degrees during the gliding motion without the flexion-extension movements in the knee and the hip joints. Therefore, during the underwater phase during starts and turns, it is a necessity that the swimmer maintains a streamlined posture. conclusIon The highest speed was maintained during the gliding motion when the knee and the hip joint angles of 180 degrees were maintained from push off from the wall to 0.8sec (1.82m). In addition, swimming speed slowed down when the involuntary movements of flexion-extension in the knee and the hip joints were observed during the gliding motion. reFerences Adrian M.J., J.M. Cooper. (1995). Biomechanics of Human Movement. Brown & Benchmark, Madison. Chatard J.C., B. Wilson. (2008). Effect of Fastskin suits on performance, drag, and energy cost of swimming. Med Sci Sports Exerc. 40(6): 1149- 1154. Elipot M., P. Hellard, R. Taiar, E. Boissiere, J.L. Rey, S. Lecat, N. Houel. (2009). Analysis of swimmers’ velocity during the underwater gliding motion. J Biomech, 42(9): 1367-1370. Havriluk R. (2007). Variability in measurement of swimming forces: a meta-analysis of passive and active drag. Research Quarterly for Exercise and Sport. 78: 32-39. Marinho D.A., V.M. Reis, F.B. Alves, J.P. Vilas-Boas, L. Machado, A.J. Silva, A.I. Rouboa. (2009). Hydrodynamic drag during gliding in swimming. J Appl Biomech, 25(3): 253-257. Mollendorf J.C., A.C. Termin II, E. Oppenheim, D.R. Pendergast. (2004). Effect of swim suit design on passive drag. Med Sci Sports Exerc. 36(6): 1029-1035. Roberts B.S., K.S. Kamel, C.E. Hedrick, S.P. Mclean, R.L. Sharp. (2003). Effect of a FastskinTM suit on submaximal freestyle swimming. Med Sci Sports Exerc. 35(3): 519-524. Speedo International Limited. (2009). http://www.speedo.co.uk/en_uk/ aqualab_ technologies/aqualab/index.html. chaPter2.Biomechanics Head Out Swimming in Water Polo: a Comparison with Front Crawl in Young Female Players Zamparo, P., Falco, s. Faculty of Exercise and Sport Sciences, University of Verona, Italy The aim of this study was to measure heart rate (HR), arm stroke efficiency (ηp) and trunk incline (TI) during head out swimming (HOS) and front crawl swimming (FCS) in young female water polo players (12 and 16.5 years of age, 3.3 and 4.8 years of practice, respectively) at different speeds (from slow to maximal). The need of keeping the head out of the water and the elbows high in HOS leads to a small (2%), albeit significant, reduction of the self select speed in comparison to FCS. During HOS the players have a larger (32%) TI while ηp is significantly reduced (21%) than during FCS. Both factors (the increase in TI and the reduction in ηp) lead to an increase of the energy requirement of this peculiar “form of locomotion in water” as confirmed, albeit indirectly, by the higher HR (10%) observed in HOS at any given speed. Key words: water polo, arm stroke efficiency, hydrodynamic resistance, IntroductIon In water polo, dribbling is the technique of moving the ball, while swimming forward, in the wake created by alternating arm strokes. With this technique the players keep the elbows high (in order to stop opposing players from gaining possession of the ball) and keep their head out of the water to see the rest of the pool and make the appropriate play. This “mode of locomotion in water” is expected to be quite expensive energetically since the need of keeping the head out of the water necessary means that the trunk is more inclined in respect to the horizontal (and this should have an effect on the hydrodynamic resistance, W d ) while keeping the elbows high probably affects the propulsive efficiency of the arm stroke (η p ). Both W d and η p are known to affect the energy cost of aquatic locomotion (C, the energy expended to cover one unit distance): C = W d / (η p η m ) (1) where η m is the mechanical efficiency of swimming (e. g. Zamparo et al., 2008). Thus the hypothesized increase in W d and decrease in η p should lead to a proportional increase in C, in respect to the condition of a “standard” front crawl stroke. Whereas in the literature it is reported that water polo players are less economical in front crawl (head down) swimming compared to competitive swimmers (for a review see Smith, 1998) to our knowledge no one has investigated so far the energy cost of swimming during head out swimming nor its determinants: i. e. the efficiency of the arm stroke and/or the hydrodynamic resistance. Moreover, as well as competitive swimmers learn how to swim efficiently (by improving swimming technique) also water polo players are expected to learn how to swim wit the head out in the most efficient and economical way. We can thus hypothesize that more expert water polo players would show a lower difference between head out swimming (HOS) and front crawl swimming (FCS) than younger, less expert ones. The aim of this study was, therefore, to investigate the trunk incline and the propelling efficiency of the arm stroke in two groups of young female water polo players (G-12: 12 years old and G-16: 16.5 years old) while swimming both styles (HOS and FCS) at different speeds (from slow to maximal). 187
BiomechanicsandmedicineinswimmingXi Methods Twenty-one young female water polo players participated to the study. They were divided into two groups: G-12: 11 players, their average age, stature and body mass were, respectively: 11.9 ± 1.4 years; 1.59 ± 0.07 m; 48.4 ± 5.3 kg; and G-16: 10 players, their average age, stature and body mass were, respectively: 16.5 ± 1.3 years; 1.64 ± 0.04 m; 65.2 ± 9.5 kg. The G-12 players had a practice of water polo of 3.3 ± 0.5 years whereas the G-16 players of 4.8 ± 0.6 years. The subjects were informed about the methods and aims of the study and gave their written informed consent to participate; parental consent was obtained for under age subjects. The experiments were performed in an indoor 25 m swimming pool. The subjects were requested to swim at constant speed and stroke rate starting, without diving, from the pool wall. The experiments were repeated at 4 speeds (self selected by the swimmers as slow, moderate, fast and maximal) and with the two styles (HOS: head out swimming and FCS: front crawl swimming) in two separate days. In the central 10 m of the pool the average speed (V, m . s -1 ), the stroke frequency (SF, Hz) and the kick frequency (KF, Hz) were measured by means of a stopwatch. The stroke length (SL, m) was then calculated as V/ SF. The arm stroke efficiency was calculated according to the simple model proposed by Zamparo et al. (2005). The model is based on the assumption that the arm is a rigid segment of length l, rotating at constant angular speed about the shoulder and yields the average efficiency for the underwater phase only, as follows: 188 η p = ((V . 0.9) / (2π . SF . l)) . (2 / π) (2) where V is the average speed of the swimmer, SF is the stroke frequency and l is the average shoulder to hand distance. In turn, l can be calculated trigonometrically by measuring the upper limb length (0.49 ± 0.02 m in G-12 and 0.50 ± 0.02 m in G-16) and the average elbow angle (EA) during the in-sweep of the arm pull. In this study, EA was not directly measured but calculated on the basis of the subject’s age based on data published by Zamparo (2006). Finally, in equation 7, the speed was multiplied by 0.9 to take into account that, in the front crawl, about 10% of forward propulsion is produced by the legs (e. g. Hollander et al. 1988). For a detailed discussion about the pro and cons of this model the reader is referred to Zamparo et al. (2005) and Zamparo (2006). During the experiments video records were taken, with a sampling rate of 50 Hz, by means of a video-camera (TS-6031PSC, CANO- PUS, UK) positioned 0.5 m below the water surface, perpendicular to the swimmer’s direction (the subjects swam in the second lane, at a distance of 7-8 m from the camera). After the experiments, the data were downloaded to a PC and analyzed using a commercial software package (Twin pro, SIMI, G). In FCS trunk incline (TI, degrees) was measured from the angle with the horizontal of the segment between the shoulder (acromion) and the hip (great trochanter) whereas in HOS, instead of the shoulder, the margin of the axilla was marked instead (since the shoulder joint is outside the water in this condition). The measurement of TI was taken, for a single passage, at the end of the in-sweep (when the hand is directly below the shoulder) since in this position the rotation around the sagittal axis is the least and has the smaller influence on the degree of rotation (see also Kjendlie et al. 2004). Finally, the subjects were equipped with a waterproof heart rate monitoring system (RS800sd, Polar, Fi) so their heart rate (HR, bpm) at the end of each trial was recorded as well. These data should indicate, albeit indirectly, whether the differences in the kinematical/biomechanical parameters between styles and groups do indeed lead to differences in the energetics of swimming. Statistical analysis was carried out by means of an ANOVA test (SPSS v17.0, SPSS Inc., Chicago Ill., USA) for repeated measures: two groups (G-12 and G-16), four speeds (V1 –V4) and two conditions (FCS: front crawl swimming and HOS: head out swimming). measurement of TI was taken, for a single passage, at the end of the in-sweep (when the hand is directly below the shoulder) since in this position the rotation around the sagittal axis is the least and has the smaller influence on the degree of rotation (see also Kjendlie et al. 2004). Finally, the subjects were equipped with a waterproof heart rate monitoring system (RS800sd, Polar, Fi) so their heart rate (HR, bpm) at the end of each trial was recorded as well. These data should indicate, albeit indirectly, whether the differences in the kinematical/biomechanical parameters between styles and groups do indeed lead to results differences in the energetics of swimming. In tables 1 and 2 are reported the average ± 1 SD values of all the inves- Biomechanics and Medicine in Swimming XI Chapter 2 Biomechanics b tigated parameters for the two groups (Table 1: G-12; Table 2: G-16) at swimming). the four speeds and in the two conditions (FCS and HOS). In both conditions RESULTS (HOS and FCS) and for both groups (G-12 and G-16), with increasing speed (from V1: slow to V4: maximal) KF and SF increase while SL and ηp decrease; moreover, with increasing speed TI decreases while HR increases (ANOVA, F (3, 57) , p < 0.001 in all cases). Statistical analysis was carried out by means of an ANOVA test (SPSS v17.0, SPSS Inc., Chicago Ill., USA) for repeated measures: two groups (G-12 and G-16), four 188 speeds (V1 –V4) and two conditions (FCS: front crawl swimming and HOS: head out were downloaded to a PC and analyzed using a commercial software package (Twin In pro, tables SIMI, 1 G). and In 2 FCS are trunk reported incline the (TI, average degrees) ± was 1 SD measured values from of all the the angle investigated with the parameters horizontal for of the two segment groups between (Table 1: the G-12; shoulder Table 2: (acromion) G-16) at the and four the speeds hip and (great in the trochanter) two conditions whereas (FCS in HOS, and HOS). instead In of both the conditions shoulder, the (HOS margin and FCS) of the and axilla for both was groups marked (G-12 instead and (since G-16), the with shoulder increasing joint speed is outside (from V1: the water slow to in V4: this maximal) condition). KF The and SF measurement increase while of TI SL was and taken, for ηp decrease; a single moreover, passage, at with the increasing end of the in-sweep speed TI (when decreases the while hand is HR directly increases below (ANOVA, the shoulder) since F(3, 57), p < 0.001 in this in position all cases). the rotation around the sagittal axis is the least and has the smaller influence on the degree of rotation (see also Table 1. Average values ± 1 SD of the investigated parameters for the Kjendlie et al. 2004). G-12 group Table 1. Average values ± 1 SD of the investigated parameters for the G-12 group V (m FCS . s -1 ) SF (Hz) SL (m ) KF(Hz) ηp TI (deg) HR (bpm) V1 0.94 ± 0.06 0.45 ± 0.12 2.22 ± 0.57 1.85 ± 0.37 0.45 ± 0.08 23.4 ± 3.99 149 ± 17 V2 1.07 ± 0.11 0.59 ± 0.05 1.81 ± 0.21 1.86 ± 0.73 0.38 ± 0.04 21.0 ± 3.85 162 ± 12 V3 1.15 ± 0.13 0.76 ± 0.10 1. 54 ± 0.18 2.01 ± 0.60 0.32 ± 0.04 18.1 ± 3.91 169 ± 11 V4 1.25 ± 0.16 0.85 ± 0.13 1.49 ± 0.26 2.50 ± 0.60 0.31 ± 0.06 13.5 ± 4.51 165 ± 11 V1 0.95 ± 0.09 0.69 ± 0.07 1.39 ± 0.18 1.56 ± 0.71 0.29 ± 0.04 33.7 ± 9.08 159 ± 14 HOS V2 1.00 ± 0.12 0.73 ± 0.07 1.38 ± 0.20 1.76 ± 0.85 0.29 ± 0.04 28.7 ± 4.62 167 ± 15 V3 1.12 ± 0.15 0.89 ± 0.15 1.30 ± 0.26 1.85 ± 0.84 0.27 ± 0.05 30.2 ± 4.97 174 ± 16 V4 1.16 ± 0.18 0.93 ± 0.16 1.28 ± 0.25 2.04 ± 0.76 0.27 ± 0.05 22.2 ± 8.06 176 ± 16 Table 2. Average values ± 1 SD of the investigated parameters for the G-16 group V (m . s -1 Finally, the subjects were equipped with a waterproof heart rate monitoring system (RS800sd, Polar, Fi) so their heart rate (HR, bpm) at the end of each trial was recorded as well. These data should indicate, albeit indirectly, whether the differences in the kinematical/biomechanical parameters between styles and groups do indeed lead to differences in the energetics of swimming. Statistical analysis was carried out by means of an ANOVA test (SPSS v17.0, SPSS Inc., Chicago Ill., USA) for repeated measures: two groups (G-12 and G-16), four speeds (V1 –V4) and two conditions (FCS: front crawl swimming and HOS: head out swimming). RESULTS In tables 1 and 2 are reported the average ± 1 SD values of all the investigated parameters for the two groups (Table 1: G-12; Table 2: G-16) at the four speeds and in the two conditions (FCS and HOS). In both conditions (HOS and FCS) and for both groups (G-12 and G-16), with increasing speed (from V1: slow to V4: maximal) KF and SF increase while SL and ηp decrease; moreover, with increasing speed TI decreases while HR increases (ANOVA, F(3, 57), p < 0.001 in all cases). Table 2. Average values ± 1 SD of the investigated parameters for the G-16 Biomechanics group and Medicine in Swimming XI Chapter 2 Biomechanics b 189 ) SF (Hz) SL (m ) KF(Hz) ηp TI (deg) HR (bpm) Table 1. Average values ± 1 SD of the investigated parameters for the G-12 group V (m . s -1 ) SF (Hz) SL (m ) KF(Hz) ηp TI (deg) HR (bpm) V1 0.94 1.01 ± 0.06 0.08 0.45 0.48 ± 0.12 0.07 2.22 2.13 ± 0.57 0.34 1.85 1.43 ± 0.37 0.48 0.45 0.43 ± 0.08 0.07 23.4 24.0 ± 3.99 5.62 149 131 ± 17 13 V2 1.07 1.15 ± 0.11 0.08 0.59 ± 0.05 0.15 1.81 2.04 ± 0.21 0.56 1.86 1.82 ± 0.73 0.31 0.38 0.39 ± 0.04 0.07 21.0 21.4 ± 3.85 5.20 162 141 ± ± 12 8 FCS FCS V3 1.15 1.27 ± 0.13 0.76 0.66 ± 0.10 0.12 1. 1.97 54 ± 0.18 0.32 2.01 2.03 ± 0.60 0.53 0.32 0.40 ± 0.04 0.06 18.1 20.0 ± 3.91 5.49 169 157 ± 11 V4 1.25 1.37 ± 0.16 0.12 0.85 0.74 ± 0.13 0.10 1.49 1.88 ± 0.26 0.27 2.50 2.40 ± 0.60 0.31 0.38 ± 0.06 13.5 14.6 ± 4.51 3.71 165 166 ± ± 11 8 V1 0.95 1.01 ± 0.09 0.12 0.69 0.60 ± 0.07 0.09 1.39 1.70 ± 0.18 0.23 1.56 1.30 ± 0.71 0.52 0.29 0.34 ± 0.04 0.05 33.7 34.4 ± 9.08 3.39 159 153 ± 14 15 HOS V2 1.00 1.13 ± 0.12 0.09 0.73 0.70 ± 0.07 0.11 1.38 1.66 ± 0.20 0.33 1.76 1.55 ± 0.85 0.55 0.29 0.34 ± 0.04 0.07 28.7 27.6 ± 4.62 3.81 167 160 ± 15 14 V3 1.12 1.24 ± 0.15 0.11 0.89 0.78 ± 0.15 0.08 1.30 1.62 ± 0.26 0.25 1.85 1.78 ± 0.84 0.69 0.27 0.33 ± 0.05 30.2 30.9 ± 4.97 3.33 174 165 ± 16 13 V4 1.16 1.33 ± 0.18 0.13 0.93 0.84 ± 0.16 0.08 1.28 1.59 ± 0.25 0.23 2.04 2.10 ± 0.76 0.61 0.27 0.32 ± 0.05 22.2 ± 8.06 4.43 176 175 ± ± 16 9 The comparison between styles (both groups considered, at all swim- Table 2. Average values ± 1 SD of the investigated parameters for the G-16 group V (m . s -1 The comparison between styles (both groups considered, at all swimming speeds) indicates that all parameters are significantly different in the two conditions (HOS and ming FCS) (ANOVA, speeds) indicates F(1, 19), p < that 0.05 all in all parameters cases). Swimming are significantly with the head different out leads in to a the small two (2%), conditions albeit ) significant, (HOS SF (Hz) reduction and SL (m FCS) ) of the (ANOVA, KF(Hz) self select speed F in comparison ηp TI (deg) HR to (bpm) FCS. (1, 19) , p < 0.05 in all During HOS the players have a larger (32%) inclination of the trunk with the horizontal cases). Swimming with the head out leads to a small (2%), albeit signifi- and a higher heart rate (7%) compared to FCS. Moreover, in HOS, SL and ηp are cant, significantly reduction reduced of the (21% self in both select cases) speed whereas in comparison SF is increased to (17%) FCS. in During respect to HOS FCS. Finally, the players KF is 10% have lower a larger during (32%) HOS than inclination during FCS. of the trunk with the The comparison between groups (both styles considered, at all swimming speeds) horizontal indicates that and there a higher are no significant heart rate differences (7%) compared between groups to FCS. (G-12 Moreover, and G-16) in in TI and KF. However, players of G-12 swim at a significantly lower pace than those of G- HOS, SL and ηp are significantly reduced (21% in both cases) whereas SF is increased (17%) in respect to FCS. Finally, KF is 10% lower during HOS than during FCS. The comparison between groups (both styles considered, at all swim- 16 (9%), with a lower SL (14%), a higher SF (8%) and a lower ηp (11%) (ANOVA, F(1, 19), p < 0.05 in all cases). Finally, HR is 5% lower in G-16 than in G-12 albeit this difference does not reach a significant level (p = 0.06). DISCUSSION ming speeds) indicates that there are no significant differences between Data reported in this study indicate that HOS is characterized by relevant differences in groups the biomechanics (G-12 and of swimming G-16) in in TI comparison and KF. with However, FCS. The players need of keeping G-12 swim the head at out a of significantly the water does lower indeed pace lead than to an increase those of G-16 TI (and (9%), thus to with an increase a lower of frontal SL area and hydrodynamic resistance) whereas the need of keeping the elbows high does (14%), indeed a lead higher to an SF increase (8%) of and SF a and lower thus ηto p (11%) a reduction (ANOVA, of the distance F (1, 19) , covered p < 0.05 per in stroke all cases). (and of Finally, the arm stroke HR is efficiency). 5% lower Both in needs G-16 do than indeed in result, G-12 as albeit hypothesized, this in an increase of the energy requirement of this peculiar “form of locomotion in water” difference does not reach a significant level (p = 0.06). as confirmed, albeit indirectly, by the higher HR in HOS than in FCS at any given speed. Interestingly, KF is lower during HOS than FCS and this suggests that these players are not able to contrast the larger trunk incline with a more frequent/forceful leg kick. dIscussIon Moreover, KF and TI do not change with the years of practice (no differences are Data observed reported between in the this two study groups indicate for these two that parameters) HOS is characterized and this suggests by that rel- more experienced swimmers essentially rely on a better arm stroke efficiency to overcome the evant differences in the biomechanics of swimming in comparison with challenges of this “swimming style”. FCS. The need of keeping the head out of the water does indeed lead to an increase of TI (and thus to an increase of frontal area and hydrodynamic resistance) whereas the need of keeping the elbows high does indeed lead to an increase of SF and thus to a reduction of the distance covered per stroke (and of the arm stroke efficiency). Both needs do indeed result, as hypothesized, in an increase of the energy requirement of this peculiar “form of locomotion in water” as confirmed, albeit indirectly, by the higher HR in HOS than in FCS at any given speed. CONCLUSIONS This study suggests that while training young water polo players is necessary to improve as much as possible the efficiency of the arm stroke. Moreover, it indicates the importance to teach them how to perform a continuous and regular leg kick to raise, as
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Biomechanics and Medicine in Swimmi
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Bibliographic information: Biomecha
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Figure 1. General biomechanical par
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Figure 2. Repeatability of the LTin
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• Without restriction; • Blinde
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etween experimental groups and cont
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Pahlen Norge AS Pahlen Norge AS Cha
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