Biomechanics and Medicine in Swimming XI

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may be assumed that the most difficult element of monofin swimming is the proper range of motion in the ankle joints; (4) an analysis of the differences between value of errors performed, suggests the parameter most differentiating the fastest from the slowest swimmer, is the angle of bend of the feet in relation to the shanks (19.5%). The angle of attack of distal part of the fin (11.5%) placed second in the ranking mentioned. The differences between values of errors in terms of the angle of bend in the proximal part of the fin (7.3%) and angle of attack of the entire fin (6.8%) was the lowest, even when most similar. (5) The errors estimated high correlated to swimming intracycle velocity. Angular Displacement [deg] 220 200 180 160 140 M900 4 16 20 30 ERROR ERROR M600 5 17 27 29 ERROR ERROR 120 M300 4 21 24 33 TIME [s] (Sampling frequency 50Hz) ERROR ERROR 100 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 KAT1ER KAT6ER KAT1COR KAT6COR KAT3ER KAT9ER KAT3COR KAT9COR Ma M100 4 ERROR 17 19 ERROR 33 M-HIGHEST SPEED SUMM OF ERRORS [%] M-LOWEST SPEED AVERAGE SD KAT 58,1 77.6 71,5 8,4 ATM 26,4 33,7 34,6 6,1 HME 22,4 33,6 34,6 6,1 HTE 29,8 36,6 42,5 8,5 Figure 2. Graph illustrating scope of errors (ER) in angle of the foot flexion in relation to shank (KAT) in time function. At left are sequences of movement illustrating the range of errors showed in the graph. Sum of errors by fastest and slowest swimmers compared to average value calculated for all swimmers. Table 1. Pearson’s correlation coefficients between value of error in cycle made by all subjects on 100-m sections, and average velocity (ranked by average velocity). (KAT) – angle of bend in foot at ankle joint; (ATM) – angle of bend in tail of monofin; (HME) – angle of attack of distal part of fin, (HTE) – angle of attack of entire surface of fin. SUBJECT KAT ATM HME HTE SUBJECT KAT ATM HME HTE M -0,94 -0,99 -0,62 -0,99 P -0,66 -0,88 -0,90 -0,89 A -0,99 -0,55 -0,72 -1,00 S -0,79 -0,96 -0,85 B -0,71 -0,94 -1,00 -0,70 N -0,77 -0,52 The following determinant movement sequences were estimated. The end of the downbeat movement, where the knee joints straighten, the legs are straight, the feet are in their lowest downbeat position, the tail is at maximum bent at the maximum angle of attack of the entire surface of the fin (Table 2(1)). The change ankle joint angle and the angle between proximal part of the fin and the feet is during the downbeat – beginning of the phase where the legs are maximally flexed and the segments of the fin are more or less parallel (Table 2(3)) and finally, during upbeat – the last part of upward movement, with legs straightened, just before flexing at the knees, at the maximum bend of the tail of the fin (Table 2(2)). The determinant movement sequence referring to the change of angle of the distal part of the fin and its entire surface is in the downbeat - the second part of legs straightening at the knees, where the shanks are more or less parallel to the direction of swimming and the monofin is more or less straight in the maximum angle of attack (Table 2(4)). During upbeat – the second part of the lifted legs straightened with the knees up, until the legs are placed more or less parallel to direction of swimming and the monofin is at maximum bend in the middle (Table 3(5)). The key elements in the movement structure of legs and monofin were also described (Table 1). chaPter2.Biomechanics Table 2. The determinant sequence of leg movements and monofin (1,2,3,4,5) arranged with the key elements in the structure of monofin and leg movements (A,B,C,D).related to occurrence of errors. dIscussIon Errors in propulsive movement structure and their impact on swimming speed, are relevant to the principle of equilibrium of momentum due to the interaction between the water and swimmer. Without errors momentum transfer between the subsequent leg segments and the monofin, is most effective (Rejman, 2006). Therefore, the determinant sequence initiated in the category of quality of momentum transfer, occurs between subsequent elements of the feet - parts of the monofin‘s chain. The swimmers tested in this study show a low level of control over feet movement while executing propulsion actions. The angle of bent of the feet in relation to the shanks is the most difficult element of the movement structure (Figure 2). Additionally, changing this angle in the function of time and layout of errors, demonstrates the least mutual similarity among the parameters tested. The dominant role of foot movement in generating propulsion is revealed in results gained from the construction of a neural network (Rejman and Ochmann, 2009) as well as research on factors supporting maintenance of consistent high infracycle monofin swimming velocity (Rejman, 2006). The aim of these suggestions was to avoid placing the fin parallel to the direction of swimming. The results confirmed that, the feet as an active (under total control of the swimmer) element in the biomechanical chain are the final link of torque transfer from the legs to the surface of the fin (Rejman, 2006). Hence, correct movement in this element of the sequence structure of propulsion seems to be important. Cognitive control of foot movement allows for self-correction of swimming technique. The tendency toward excessive plantar flexion of the feet (observed generally, not only in the research group) thus seems unjustified from the point of view of swimming efficiency An analysis of the value of sum of errors made by swimmers indicated similarities between angle of bend in the tail of the monofin (ATM) and angle of attack of the distal part of the fin (HME) (Figure 2). Similarities were also noted when comparing the values of difference between angle of bend in the tail of the monofin (ATM) and angle of attack of the entire surface of the fin (HTE) This may indicate that the bending of the tail of the fin, influences the change in shape of the monofin’s surface. It is accepted that the tail is the place where transfer of torque, generated by the legs, to the surface of the fin is performed (Rejman, 2006). With this in mind, the tail is the key element in analyzing the biomechanical chain, dividing it into parts consisting of leg segments and monofin segments. Supporting this thesis are results showing that the optimal plantar flexion during downbeat, limits the bend of the tail, as a result optimizing the angle of attack of the proximal part of the fin. Optimal dorsal flexion of the feet during upbeat causes greater tail bending and consequently, the angle of attack of the distal part and entire fin, achieves optimum range in both phases of the cycle (Rejman and Ochmann, 2009). These suggestions are confirmed in the present work. Greater optimization of tail bend, within limits established in the 161
BiomechanicsandmedicineinswimmingXi functional model (forming an isolated sequence) leads to the appearance of reserves in swimming technique, supporting the achievement of maximum swimming speed (Rejman and Ochmann, 2009). Due to optimal mutual actions of the feet, tail and the parts of the fin with speed, the formation of vortices occurs. These become an additional source of propulsion. Stable vortex circulation creates additional momentum due to velocity changes of water mass, produced by the rotational velocity of the vortex (Colman et al., 1999). It seems that the efficient transfer of torque over the surface of the fin, no matter if directly from leg movements, is subordinated to the hydrodynamic conditions of water flow over the surface of the fin. In this aspect, the dynamic transfer system, displayed as changes to the angle of attack of the monofin, changes the structure of water flow over its surface, and appears to be a key to effective swimming. The results obtained correspond to the analysis of particular components of force generated on the surface of the fin, with respect to the change in intracycle velocity (Colman et al., 1999; Rejman et al., 2006) (Table 2 - B, D) – in extreme upper and lower feet position, where the legs are straight at the ankle joint, the monofin bends at the tail, and its midsection is placed parallel to the direction of swimming. The research cited indicates that the main source of propulsion in this part of the cycle are drag and lift forces as well as accompanying components due to vortex induced momentum and the flexion of the fin. These same authors believe that maintaining the velocity cited, plays a main role in placing the distal part of the fin parallel to the direction of swimming (Table 2 – (A, C) - maximum bend of the distal part and entire surface of the fin, during change of direction of edge movement). In the sequences described, the energy essential to swimmer propulsion emanates from both additional mass slides away from the edge and acceleration reaction. The diagnostic value of the parameters analyzed was confirmed in an earlier constructed model of functional swimming and monofin technique (Rejman and Ochmann, 2009). It was also confirmed that, the greater the influence of the parameter on swimming speed, the more difficult the performance of proper movement in relation to this parameter. The errors indicated concern the fragments, which registered the highest intracycle velocity (confirmed by correlation coefficients (Table 1)) suggesting that, the achievement of maximum intracycle speed, is a consequence of proper execution of the determinant sequence of movement. No difference was demonstrated in terms of the change in angular foot movement, in subjectively interpreted conditions, ensuing from fatigue during swimming of subsequent distances of the trial. Therefore, there is a basis for the objective evaluation of the reliability of the errors, which occurred. The procedures outlining determinant sequences, on the basis of errors analyzed, create an empirical foundation for treating this sequence as a tool for evaluating monofin swimming technique (Table 2). conclusIon Precise control of foot movement, alows for achieving a dynamic system transferring torque, as a basis of propulsion, which creates momentum, bending the tail of the fin during transfer, thus changing the shape of the fin and the structure of water flow over its surface. This same proper sequence of propulsive movement creates conditions for using the surface of the monofin to achieve maximum speeds. Therefore, it is justified to assign key elements to monofin swimming technique, for the quantification of its quality, and for the anticipation and elimination of errors during the technical training. reFerences Colman V, Persyn U, Ungerechts BE. (1999). A mass of water added to swimmer’s mass to estimate the velocity in dolphin-like swimming bellow the water surface. Biomechanics and Medicine of Swimming VIII. Keskinen K, Komi P, Hollander A. (eds.). Gummerus Printing, Jyvaskyla, (pp) 89 - 94. Persyn U, Colman V, Zhu JP. (1997). Scientific concept and educational transfer in undulating competitive strokes in Belgium. Koelner 162 Schwimmsporttage 1996, Sport-Fahnemann-Verlag, Boikenem, (pp 34-40). Rejman M, Ochmann B. (2009). Modeling of monofin swimming technique: optimization of feet displacement and fin strain. J.Applied Biomech, 25: 340-350 Rejman, M. (2006). Influencing of timing delay on monofin intra-cycle swimming velocity. Vilas-Boas JP, Alves F, Marques A. (eds.). Biomechanics and Medicine in Swimming X. Portuguese Journal of Sport Sciences, 85–88. Richard A Schmidt RA Lee T. (2005). Motor control and learning. a behavioral emphasis - 4th Edition. Champaign: Human Kinetics. Shuping L and Sanders R. (2002). Mechanical properties of the fin. Scientific Proceedings of XX International Symposium on Biomechanice in Sports. Gianikellis K. (eds.) Caceres, (pp) 479-481. Wu Yao-Tsu T. (1971). Hydrodynamics of swimming propulsion. Part 1. Swimming of a two-dimensional flexible plate at variable forward speeds in an inviscid fluid. J. Fluid Mech. 46, 337-355.
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Pahlen Norge AS Pahlen Norge AS Cha
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Biomechanics and Medicine in Swimming XI

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