Biomechanics and Medicine in Swimming XI

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In Figure 3 an example of the information provided to the coach and swimmer is illustrated. From the force data it is possible to determine the block time, the time of first movement, peak horizontal and vertical forces as well as centre of pressure information. The vision system information is used to provide information relevant to the flight phase of the start i.e. the flight distance and flight time. The timing of the first stroke as well as the number of strokes through to the 15 m mark can be determined using the acceleration data. The inclusion of the vision data in the report provides a detailed initial understanding of the force data collected during the block and flight phases. Figure 3. Track start analysis combining vision systems, force profiles and acceleration data. dIscussIon Individual monitoring components have been developed that enable parameters relevant to the performance of various components of the start phase of swimming to be quantified. The three main monitoring components include vision information, force profiles and acceleration data through a network of distributed wireless nodes. Each of these components is able to provide feedback to the coaches and the athletes but it is the synchronisation and integration that allows a greater level of understanding to be obtained. From the video images it is possible to provide qualitative feedback immediately after each start. By synchronising this with the force platform information, quantitative values during the block phase can be calculated and fed back to the coaches and swimmers. An example of this integrated analysis approach was shown with the elite level athlete whilst undergoing an intervention in their starting technique resulted in quantifiable visible differences in both the horizontal and vertical force components. The addition of wireless acceleration information is unique to this analysis of swimming starts where information on stroking and timing is included in the data analysis. Results from a number of trials of the integrated system have highlighted the reliability of the data and the impact of interventions. The synchronisation of data from a number of monitoring modalities provides accurate, timely and relevant feedback to both the coaches and chaPter2.Biomechanics athletes supporting enhanced impact from testing. Future work will be focussed on the development of a more complete understanding of force and acceleration data and the implications for skill and performance improvement throughout the various phases of the start. conclusIon An integrated component-based system has been developed that allows swimming starts to be analysed in greater detail than possible with previous systems via integrated video, force and acceleration data. Feedback was provided to the coach and athlete for interventions in training to be made and the impacts to be quantified in detail. Future work will examine the impact on starting performance of the wedge included on the next generation Omega OSB11 starting blocks, which are likely to be used in the London 2012 Olympic Games. reFerences Arellano, R., Llana, S., Tella, V., Morales, E. & Mercade, J. (2005). A Comparison CMJ, Simulated and Swimming Grab Start Force recordings and their Relationships with the Start Performance. Proceedings of XXIII International Symposium on Biomechanics in Sports, China, 923-926. Davey, N., Anderson, M. & James, D. (2008). Validation Trial of an Accelerometer-Based Sensor Platform for Swimming. Sports Technology, 1,(4-5), 202-207. James, D., Davey, N. & Rice, T. (2004). An Accelerometer Based Sensor Platform for Insitu Elite Athlete Performance Analysis. Proceedings of IEEE Sensors, Austria, 3, 1373-1376. Mason, B., Alcock, A. &Fowlie, J. (2007). A Kinetic Analysis and Recommendations for Elite Swimmers Performing the Sprint Start. Proceedings of XXV International Symposium on Biomechanics in Sports, Brazil, 192-195. Ohji, Y. (2006). MEMS Sensor Application for the Motion Analysis in Sports Science. ABCM Symposium Series in Mechantronics, 2, 501-508. Ruschel, C., Araujo, L., Pereira, S. & Roesler, H. (2007). Kinematical Analysis of the Swimming start: Block, Flight and Underwater Phases. Proceedings of XXV International Symposium on Biomechanics in Sport, Brazil, 385-388. Slawson, S. (2010). Intelligent User Centric Components for Harsh Distributed Environments. Thesis Loughborough University. 61
BiomechanicsandmedicineinswimmingXi Hydrodynamic Characterization of the First and Second Glide Positions of the Underwater Stroke Technique in Breaststroke costa, l. 1 ; ribeiro, J. 1 ; Figueiredo, P. 1 ; Fernandes, r.J. 1 ; Marinho, d. 2,3 ; silva, A.J. 3,4 ; rouboa, A. 3,4 ; Vilas-Boas, J.P. 1 ; Machado, l. 1 1 University of Porto, Faculty of Sport, Cifi2d, Porto, Portugal 2 University of Beira Interior, Covilhã, Portugal 3 Research Center In Sports, Health and Human Development, Vila Real, Portugal 4 University of Trás-os-Montes and Alto Douro, Vila Real, Portugal The aim of the present study was to characterize two different ventral glide positions, both used after start and turns: the arms extended at the front, and the arms extended along the trunk, respectively the first and the second glide positions of the breaststroke underwater stroke. Inverse Dynamics was used for obtaining the passive drag and the drag coefficient, based upon the velocity to time curve of each glide, monitored through a swim-meter. The first glide position presented lower values of drag and drag coefficient, managing to reach higher velocities. The cross sectional area (planimetry) values were lower for first glide position in comparison with the second one (759.95 ±124.12 cm2 vs. 814.46 ± 111.23 cm2). These results point out the need of technical evaluation and control in order to reduce drag during swimming performance. KeY Words: swimming, breaststroke, passive drag, drag coefficient, gliding position IntroductIon In swimming the total event time is determined by the start, swim, turn and finish partial times (Haljand and Saagpakk, 1994). Starts and turns appear to be a significant part of the total swimming event time (Vilas- Boas and Fernandes, 2003). Chatard et al. (1990) stated that the gliding phase after starts and turns corresponds to 10 to 25% of the total event time (depending on events and the length of the swimming pool). D’Acquisto et al. (1988) showed that, during the breaststroke events, the gliding phases represent 44% of the total swimming time. These authors showed that the gliding phase distinguishes elite from good level breaststroke swimmers, with higher gliding time for the elite swimmers. Race analysis suggested that rather than the start technique used by swimmers; it is the position under the water that mostly determines the success of the start (Cossor and Mason, 2001). Therefore, it is essential to analyse and understand this phase. The passive drag of swimmers moving underwater in a streamlined position has been measured experimentally (Clarys, 1979; Kolmogorov et al., 1997; Lyttle et al., 2000; Toussaint et al., 2004; Vilas- Boas et al., in press). However, there are other gliding phases in which the swimmers assume a prone position but with the arms extended at the side of the trunk, as in the second glide position after the breaststroke underwater arm stroke. To our knowledge, these two glide positions were compared experimentally only by Vilas-Boas et al. (in press), and numerically by Marinho et al. (2009). In both cases, the glides were compared in common velocities, not considering the total range of velocities at which they are usually performed. The aim of the present study was to experimentally characterize the first and second gliding positions of the breaststroke underwater stroke used after starts and turns at the total range of velocities commonly performed, considering: (i) gliding velocity (v); (ii) body cross sectional area (S); (iii) drag coefficient (C D ), and (iv) passive drag (D). Methods Six Portuguese national level male swimmers (18.2 ± 4.0 years old, 178.2 ± 9.0 cm of height and 64.4 ± 11.4 kg of body mass) participated in this 62 study. Testing sessions were conducted in a 25 m pool, 2 m deep, with water temperature at 27.5 ºC. It was used a similar methodology to the described in Vilas-Boas et al. (in press), namely the S determination using planimetry, and the passive drag assessed through inverse dynamics based upon the velocity to time (v (t) ) curve of each glide, monitored through a swim-meter (Lima et al. 2006). Acceleration (a) was obtained through the numerical derivative of the velocity curve. The drag force was computed using the expression: D = m . a . (1) To quantify the drag coefficient, the following equation was used, assuming water density (ρ) as 1000 kg/m3 : C D = 2 D / ρ S v 2 (2) Each swimmer performed 3 repetitions of the breaststroke underwater stroke, at maximal intensity (2 min of interval). During the rest interval, swimmers received proper feedback in order to improve their performance. The video images and data processing (v (t) curves and acceleration to time curves representations) of the first and second glide of the underwater breaststroke were obtained according to Vilas-Boas et al. (in press). Not all swimmers attained all velocity values, being retained the v values (independently in each glide) for which there were values from at least three swimmers. The processes of D and C D calculations were described also in Vilas-Boas et al. (in press). results The main results of this study are presented in Table 1 and in Figures 1 and 2. Table 1 shows the S values for each swimmer in the first and second glides while Fig. 1 and 2 show D and C D , respectively, for each glide and for all v values attained. Table 1. Individual and mean ± SD values of the cross-sectional area of the body (S) assessed for the two studied breaststroke gliding positions. Swimmer S (cm2) for first glide position S (cm2) for second glide position 1 971.13 942.1 2 719.73 886.91 3 641.7 668.47 4 689.17 769.24 5 692.6 718.05 6 845.34 901.99 Mean ± SD 759.95 ±124.12 814.46 ± 111.23 The mean ± SD v values for the first and second glide positions were 1.50 ± 0.22m/s and 1.15 ± 0.24m/s, respectively. The first glide presented higher values of mean v, while the second gliding was characterized by higher values of acceleration (0.61 ± 0.24m/s 2 to 0.66 ± 0.06m/ s 2 versus 0.40 ± 0.06 m/s 2 to 0.63 ± 0.16m/s 2 for common values of v, second and first glide respectively). The common velocities for the two gliding phases were 1.20, 1.30, 1.40 and 1.50m/s (Fig. 1 and 2) Drag (N) first glide 80 second glide 70 60 50 40 30 20 10 0 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Velocity (m/s) Figure 1. Drag versus velocity curve in two distinct gliding positions: first glide and second glide of the breaststroke underwater stroke
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Pahlen Norge AS Pahlen Norge AS Cha
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