Biomechanics and Medicine in Swimming XI

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Figure 4. Overlay scatter gram from horizontal velocity and vertical velocity according to the cadence imposed. dIscussIon The aim of this study was to analyze the relationships between musical cadence and kinematical characteristics of a basic head-out aquatic exercise, when immersed to the breast. Main data suggests that expert and fit subjects increase segmental velocity with increasing musical cadence to avoid the decrease of the segmental range of motion. There was a very high relationship between cycle period and the cadence, with a decrease of the time variable throughout the incremental protocol. On one hand, there were no significant relationships between any of the displacement variables and the musical cadence. On the other habd, most of the velocity variables were moderate, positive and significantly related to the musical cadence. Cycle period is considered as being: P = n ∑ ti i= 1 (1) Where P is the cycle period (in s) and t is the duration (in s) of each phase, being the exercise composed by i partial phases. The duration of each phase can be computed as: d i t i = (2) vi Where t i is the duration of each partial phase of the exercise (in s), d i is the segment displacement (in m) during the partial phase and v i is the segment velocity (in m·s -1 ) during the partial phase. Although it was hypothesized in the introduction section that increasing cadence would impose a decrease of the segments range of mo- chaPter2.Biomechanics tion; the subjects decreased the t i through an increase of the v i . It can be speculated that this specific motor control, as well as, biomechanical strategy, can be related to the subjects’ profile. They were: (i) expert subjects, i.e., head-out aquatic exercise instructors that are aware from the need to maintain at all time a large range of motion performing basic exercises, independently from the cadence imposed and; (ii) very active subjects that not only are aware from this technical tips, but are also physically fit, allowing them to maintain such range of motion at different musical cadences. As a conclusion, expert and fit subjects seem to increase segmental velocity with increasing cadences to avoid the decrease of the segmental range of motion. reFerences Abdel-Aziz Y, Karara, H. (1971). Direct linear transformation: from comparator coordinates into object coordinates in close range photogrammetry. Proceedings of the Symposium on close-range photogrammetry, p. 1-18, Church Falls. Barbosa TM, Keskinen KL, Fernandes RJ, Colaço P, Lima AB, Vilas- Boas JP. (2005). Energy cost and intracyclic variation of the velocity of the centre of mass in butterfly stroke. Eur J Appl Phys 93:519-523. Barbosa TM, Marinho DA, Bragada JA, Reis VM, Silva AJ. (2009a). Physiological assessment of head-out aquatic exercises in healthy subjects: a qualitative review. J Sports Sci Med. 8: 179-189 Barbosa TM, Sousa V, Silva AJ, Reis V, Marinho DA, Bragada JA. (2009b). Effects of music cadence in the acute physiological adaptations to head-out aquatic exercises. J Strength Cond Res. Epub ahead of print de Leva P. (1996). Adjustments to Zatsiorsky-Seluyanov’s segment inertia parameters. Journal of Biomechanics 29:1223-1230. Hoshijima Y, Torigoe K, Yamamoto M, Nishimura S, Abo N, Imoto M, Miyachi M, Onodera S. (1999). Effects of music rhythm on heart rate and oxygen uptake during squat exercises in water and on land. Biomechanics and Medicine in Swimming VIII, p. 337-339. Gummerus Printing. Kinder T, See J. (1992). Aqua Aerobics - A Scientific Approach. Dubuque: Eddie Bowers Publishing Vilas-Boas JP, Cunha P, Figueiras T, Ferreira M, Duarte J. (1997). Movement analysis in simultaneous swimming techniques. Cologne Swimming Symposium. Verlag. p.95-103. Sport Fahnemann Winter D (1990). Biomechanic and Motor Control of Human Movement. Chichester: John Wiley & Sons. 139
BiomechanicsandmedicineinswimmingXi Influence of Swimming Speed on the Affected- and Unaffected-Arm Stroke Phases of Competitive Unilateral Arm Amputee Front Crawl Swimmers osborough, c.d. 1 , Payton, c.J. 1 , daly, d.J. 2 1 Manchester Metropolitan University, Alsager, United Kingdom 2 Katholieke Universiteit Leuven, Leuven, Belgium The purpose of this study was to determine whether the arm stroke phases used by competitive unilateral arm amputee crawl swimmers differed between their affected and unaffected sides and whether these phases changed with an increase in speed. Thirteen highly-trained swimmers were video-taped underwater from two side-views during five increasingly faster 25 m front crawl trials. At all swimming speeds, the stroke phases of the affected and unaffected arms differed significantly. As speed increased, the duration of the affected-arm’s Entry and Glide phase and the unaffected-arm’s Pull phase decreased significantly; the duration of both arms’ Push phase increased significantly. The amputees used a coordination strategy that asymmetrically adjusted their arm movements to maintain the stable repetition of their overall stroke cycle at different speeds. Key words: swimming; disability sport; Motor control; Biomechanics IntroductIon Stroke phases have been frequently used to describe the propulsive and non-propulsive arm actions of able-bodied front crawl swimmers. Maglischo et al. (1988) reported that while there were four propulsive phases in the front crawl underwater arm stroke action: (1) Downsweep; (2) Insweep; (3) Outsweep; and (4) Upsweep, able-bodied swimmers were unable to generate large propulsive forces in more than two of these phases. Later, Chollet et al. (2000), when formulating the Index of Coordination for front crawl, separated the complete action of the arm stroke cycle into four distinct phases: (A) Entry and Catch; (B) Pull; (C) Push; (D) Recovery, of which they assumed, B and C were propulsive and A and D were non-propulsive. For competitive swimmers with a single elbow-level amputation, the roles that the affected- and unaffected-arm have within the front crawl arm stroke cycle may differ from each other. It would be expected that the primary function of the unaffected-arm is to generate propulsion. However, uncertainty remains as to whether the affected-arm of a unilateral arm amputee can contribute effectively to propulsion at swimming speeds higher than 1 m∙s -1 . Rather, the affected-arm might simply function to control inter-arm asymmetry so that stable repetition of the overall arm stroke cycle is maintained. Understanding the roles of both the affected- and unaffected-arm during the stroke phases would be of great practical importance to swimmers, teachers and coaches. No examination of the arm stroke phases has been undertaken with a single homogenous group of highly-trained swimmers with a single-arm amputation. For unilateral arm amputee front crawl swimmers, increases in swimming speed are achieved by increasing stroke frequency (Osborough et al., 2009). However, it is unclear how these swimmers vary the duration of their arm stroke phases in order to accommodate an increase in stroke frequency and swimming speed. The purpose of this study was to determine if the arm stroke phases used by competitive unilateral arm amputee front crawl swimmers differed between their affected and unaffected sides and whether these phases altered with an increase in swimming speed. Methods Thirteen (3 male and 10 female) competitive swimmers (age 16.9 ± 3.1 yrs) participated in this study. All participants were single-arm amputees, at the level of the elbow. The mean 50 m front crawl personal best time was 32.7 ± 3.1 s. Twelve of the swimmers competed in the Inter- 140 national Paralympic Committee S9 classification for front crawl; one male swimmer competed in the S8 classification. The procedure for the data collection was approved by the Institutional Ethics Committee. All participants provided written informed consent before taking part in the study. Participants completed five 25 m front crawl trials. Seven of the swimmers performed the trials from slow to maximum swimming speed (SS max ); the remainder performed the trials from maximum to slow swimming speed. To control for the effects of the breathing action on the swimming stroke, participants were instructed not to take a breath through a 10 m test section of the pool. Two digital video camcorders (Panasonic NVDS33), sampling at 50 Hz with a shutter speed of 1/350 s were used to film the participants. Each of the camcorders was enclosed in a waterproof housing suspended underwater from one of two trolleys that ran along the side of the pool, parallel to the participants’ swimming direction. This set-up enabled the participants to be video-taped under the water, from opposite sides, over the 10 m test section. The digital video footage was transferred to a laptop computer and analysed using SIMI Motion 7.2 software. Three consecutive, nonbreathing stroke cycles for each participant, were then selected for analysis. The estimated locations of the gleno-humeral joint centre and the elbow joint centre of both the affected and unaffected arms were digitised at 50 Hz to obtain the angular position of the upper-arms, as a function of time. Before filming, the skin overlaying the joint centres was marked with black pen to help estimate their location. At 80%, 85%, 90%, 95% and 100% of each participant’s SS max individual arm stroke phases, expressed as a percentage of the duration of the complete arm stroke cycle, were determined from the angle made by the shoulder-to-elbow position vector relative to the horizontal. Each upper-arm movement was divided into four phases (Fig. 1): Entry and Glide (A); Pull (B); Push (C); and Recovery (D): (A) Entry and Glide: from where the elbow joint centre entered the water (0°) to where the shoulder-to-elbow position vector made an angle of 25° with the horizontal. This latter position corresponded to a point where typically the swimmers actively initiated extension of their affected-arm. (B) Pull: from the end of the Entry and Glide (25°) to where the shoulder-to-elbow position vector made an angle of 90° with the horizontal. (C) Push: from the end of the Pull (90°) to where the shoulder-toelbow position vector made an angle of 155° with the horizontal. This latter position corresponded to a point where, as a result of the rolling action of the swimmers’ trunk and the bow-wave created by the swimmers’ movement through the water, the most-distal part of the swimmers’ affected-arm typically exited the water. (D) Recovery: from the end of the Push (155°) to where the elbow joint centre entered the water (360°). Figure 1. Divisions of the arm stroke phases: (A) Entry and Glide; (B) Pull; (C) Push; and (D) Recovery for a unilateral arm amputee front crawl swimmer.
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Figure 2. Repeatability of the LTin
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Pahlen Norge AS Pahlen Norge AS Cha
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