Net forces during tethered simulation of underwater streamlined gliding and kicking techniques of the freestyle turn

Weassessed the net forces created when towing swimmers while gliding and kicking underwater to establish an appropriate speed for initiating underwater kicking, and the most effective gliding position and kicking technique to be applied after a turn. Sixteen experienced male swimmers of similar body shape were towed by a motorized winch and pulley system. A load cell measured net force (propulsive force - drag force) at speeds of 1.6, 1.9, 2.2, 2.5 and 3.1 m· s-1 . At each speed, the swimmers performed a prone streamline glide, a lateral streamline glide, a prone freestyle kick, a prone dolphin kick and a lateral dolphin kick. A two-way repeated-measures analysis of variance revealed significant differences between the gliding and kicking conditions at different speeds. The results demonstrated an optimal range of speeds (1.9 to 2.2 m· s-1 ) at which to begin underwater kicking to prevent energy loss from excessive active drag. No significant differences were found between the prone and lateral streamline glide positions or between the three underwater kicking techniques. Therefore, there appears to be no significant advantage in using one streamlining technique over another or in using one kicking style over another.     

Net forces during tethered simulation of underwater streamlined gliding and kicking techniques of the freestyle turn

We assessed the net forces created when towing swimmers while gliding and kicking underwater to establish an appropriate speed for initiating underwater kicking, and the most effective gliding position and kicking technique to be applied after a turn. Sixteen experienced male swimmers of similar body shape were towed by a motorized winch and pulley system. A load cell measured net force (propulsive force - drag force) at speeds of 1.6, 1.9, 2.2, 2.5 and 3.1 m x s(-1). At each speed, the swimmers performed a prone streamline glide, a lateral streamline glide, a prone freestyle kick, a prone dolphin kick and a lateral dolphin kick. A two-way repeated-measures analysis of variance revealed significant differences between the gliding and kicking conditions at different speeds. The results demonstrated an optimal range of speeds (1.9 to 2.2 m x s(-1)) at which to begin underwater kicking to prevent energy loss from excessive active drag. No significant differences were found between the prone and lateral streamline glide positions or between the three underwater kicking techniques. Therefore, there appears to be no significant advantage in using one streamlining technique over another or in using one kicking style over another.     

Accuracy of pacing during breaststroke swimming using a novel pacing device,the Aquapacer

Generally, swimmers pace themselves using their own judgement and the poolside clock during swimming training, fitness testing protocols or scientific investigation. The Aquapacer is a new pacing device that can be used to pace the swimming speed or stroke rate of the swimmer. The aims of this study were to determine if breaststroke swimmers could pace accurately during submaximal swimming using a poolside clock (Study 1) and the Aquapacer (Study 2), at swimming speeds at, just above and just below maximal 200 m time-trial speeds (using the Aquapacer, Study 3) and under three different race pacing conditions (using the Aquapacer, Study 4). Between 8 and 15 male national or club standard 200 m breaststroke swimmers participated in each of the studies. The swimmers in Study 2, despite being less well trained than the swimmers in Study 1 and part of a more heterogeneous group in terms of swimming performance, repeatedly demonstrated less random error in pacing, suggesting that the Aquapacer may be preferable to the poolside clock when swimmers are being required to pace accurately. The Aquapacer also enabled swimmers to pace accurately at race-specific swimming speeds (until fatigue precluded them from holding pace) (Study 3), and through a change in pace at race-specific speeds (Study 4), which suggests that it may be of use in entraining racing strategies.     

Accuracy of pacing during breaststroke swimming using a novel pacing device,the Aquapacer™

Generally, swimmers pace themselves using their own judgement and the poolside clock during swimming training, fitness testing protocols or scientific investigation. The Aquapacer? is a new pacing device that can be used to pace the swimming speed or stroke rate of the swimmer. The aims of this study were to determine if breaststroke swimmers could pace accurately during submaximal swimming using a poolside clock (Study 1) and the Aquapacer? (Study 2), at swimming speeds at, just above and just below maximal 200 m time-trial speeds (using the Aquapacer?, Study 3) and under three different race pacing conditions (using the Aquapacer?, Study 4). Between 8 and 15 male national or club standard 200 m breaststroke swimmers participated in each of the studies. The swimmers in Study 2, despite being less well trained than the swimmers in Study 1 and part of a more heterogeneous group in terms of swimming performance, repeatedly demonstrated less random error in pacing, suggesting that the Aquapacer? may be preferable to the poolside clock when swimmers are being required to pace accurately. The Aquapacer? also enabled swimmers to pace accurately at racespecific swimming speeds (until fatigue precluded them from holding pace) (Study 3), and through a change in pace at race-specific speeds (Study 4), which suggests that it may be of use in entraining racing strategies.     

The force-time profile of elite front crawl swimmers

In this study, we used recently developed technology to determine the force-time profile of elite swimmers, which enabled coaches to make informed decisions on technique modifications. Eight elite male swimmers with a FINA (Federation Internationale de Natation) rank of 900+ completed five passive (streamline tow) and five net force (arms and leg swimming) trials. Three 50-Hz cameras were used to video each trial and were synchronized to the kinetic data output from a force-platform, upon which a motorized towing device was mounted. Passive and net force trials were completed at the participant's maximal front crawl swimming velocity. For the constant tow velocity, the net force profile was presented as a force-time graph, and the limitation of a constant velocity assumption was acknowledged. This allowed minimum and maximum net forces and arm symmetry to be identified. At a mean velocity of 1.92+0.06 m s?1, the mean passive drag for the swimmers was 80.3+4.0 N, and the mean net force was 262.4+33.4 N. The mean location in the stroke cycle for minimum and maximum net force production was at 45% (insweep phase) and 75% (upsweep phase) of the stroke, respectively. This force-time profile also identified any stroke asymmetry.     

Growth influences biomechanical profile of talented swimmers during the summer break

This study aimed to analyse the effect of growth during a summer break on biomechanical profile of talented swimmers. Twenty-five young swimmers (12 boys and 13 girls) undertook several anthropometric and biomechanical tests at the end of the 2011–2012 season (pre-test) and 10 weeks later at the beginning of the 2012–2013 season (post-test). Height, arm span, hand surface area, and foot surface area were collected as anthropometric parameters, while stroke frequency, stroke length, stroke index, propelling efficiency, active drag, and active drag coefficient were considered as biomechanical variables. The mean swimming velocity during an all-out 25 m front crawl effort was used as the performance outcome. After the 10-week break, the swimmers were taller with an increased arm span, hand, and foot areas. Increases in stroke length, stroke index, propelling efficiency, and performance were also observed. Conversely, the stroke frequency, active drag, and drag coefficient remained unchanged. When controlling the effect of growth, no significant variation was determined on the biomechanical variables. The performance presented high associations with biomechanical and anthropometric parameters at pre-test and post-test, respectively. The results show that young talented swimmers still present biomechanical improvements after a 10-week break, which are mainly explained by their normal growth.     

The accuracy of computational fluid dynamics analysis of the passive drag of a male swimmer

The aim of this study was to build an accurate computer-based model to study the water flow and drag force characteristics around and acting upon the human body while in a submerged streamlined position. Comparisons of total drag force were performed between an actual swimmer, a virtual computational fluid dynamics (CFD) model of the swimmer, and an actual mannequin based on the virtual model. Drag forces were determined for velocities between 1.5 m/s and 2.25 m/s (representative of the velocities demonstrated in elite competition). The drag forces calculated from the virtual model using CFD were found to be within 4% of the experimentally determined values for the mannequin. The mannequin drag was found to be 18% less than the drag of the swimmer at each velocity examined. This study has determined the accuracy of using CFD for the analysis of the hydrodynamics of swimming and has allowed for the improved understanding of the relative contributions of various forms of drag to the total drag force experienced by submerged swimmers.     

The accuracy of computational fluid dynamics analysis of the passive drag of a male swimmer

The aim of this study was to build an accurate computer-based model to study the water flow and drag force characteristics around and acting upon the human body while in a submerged streamlined position. Comparisons of total drag force were performed between an actual swimmer, a virtual computational fluid dynamics (CFD) model of the swimmer, and an actual mannequin based on the virtual model. Drag forces were determined for velocities between 1.5 m/s and 2.25 m/s (representative of the velocities demonstrated in elite competition). The drag forces calculated from the virtual model using CFD were found to be within 4% of the experimentally determined values for the mannequin. The mannequin drag was found to be 18% less than the drag of the swimmer at each velocity examined. This study has determined the accuracy of using CFD for the analysis of the hydrodynamics of swimming and has allowed for the improved understanding of the relative contributions of various forms of drag to the total drag force experienced by submerged swimmers.     

Variability in measurement of swimming forces: a meta-analysis of passive and active drag

An analysis was conducted to identify sources of true and error variance in measuring swimming drag force to draw valid conclusions about performance factor effects. Passive drag studies were grouped according to methodological differences: tow line in pool, tow line in flume, and carriage in tow tank. Active drag studies were grouped according to the theoretical basis: added and/or subtracted drag (AAS), added drag with equal power assumption (AAE), and no added drag (ANA). Data from 36 studies were examined using frequency distributions and meta-analytic procedures. It was concluded that two active methods (AAE and ANA) had sources of systematic error and that one active method (AAS) measured an effect that was different from that measured by passive methods. Consistency in drag coefficient (Cd) values across all three passive methods made it possible to determine the effects of performance factors.     

Variability in Measurement of Swimming Forces

An analysis was conducted to identify sources of true and error variance in measuring swimming drag force to draw valid conclusions about performance factor effects. Passive drag studies were grouped according to methodological differences: tow line in pool, tow line in flume, and carriage in tow tank. Active drag studies were grouped according to the theoretical basis: added and/or subtracted drag (AAS), added drag with equal power assumption (AAE), and no added drag (ANA). Data from 36 studies were examined using frequency distributions and meta-analytic procedures. It was concluded that two active methods (AAE and ANA) had sources of systematic error and that one active method (AAS) measured an effect that was different from that measured by passive methods. Consistency in drag coefficient (Cd) values across all three passive methods made it possible to determine the effects of performance factors.     

Quantifying stroke coordination during the breathing action in front-crawl swimming using an instantaneous net drag force profile

Abstract

This study used both an instantaneous net drag force profile and a symmetry timing to evaluate the effect of the breathing action on stroke coordination. Twenty elite swimmers completed a total of six randomised front-crawl towing trials: (i) three breathing trials and (ii) three non-breathing trials. The net drag force was measured using an assisted towing device mounted upon a Kistler force platform, and this equipment towed the swimmer at a constant speed. The net drag force profile was used to create a stroke symmetry index for each swimming trial. Analysis using the symmetry indices identified that the majority of participants demonstrated an asymmetrical instantaneous net drag force stroke profile in both the breathing and non-breathing conditions, despite no significant differences in the time from finger-tip entry to finger-tip exit. Within the breathing condition, the faster swimmers compared to the slower swimmers demonstrated a lesser percentage of overlap between stroke phases on their breathing stroke side. During the non-breathing condition, the faster participants compared to the slower swimmers recorded a reduction in the percentage of overlap between stroke phases and less duration in the underwater stroke on their breathing stroke side. This study identified that the majority of participants demonstrated an asymmetrical net drag force profile within both conditions; however, asymmetry was less prevalent when examining with only the timing symmetry index.     

The force–time profile of elite front crawl swimmers

Abstract

In this study, we used recently developed technology to determine the force–time profile of elite swimmers, which enabled coaches to make informed decisions on technique modifications. Eight elite male swimmers with a FINA (Federation Internationale de Natation) rank of 900+ completed five passive (streamline tow) and five net force (arms and leg swimming) trials. Three 50-Hz cameras were used to video each trial and were synchronized to the kinetic data output from a force-platform, upon which a motorized towing device was mounted. Passive and net force trials were completed at the participant's maximal front crawl swimming velocity. For the constant tow velocity, the net force profile was presented as a force–time graph, and the limitation of a constant velocity assumption was acknowledged. This allowed minimum and maximum net forces and arm symmetry to be identified. At a mean velocity of 1.92 ± 0.06 m · s^?1, the mean passive drag for the swimmers was 80.3 ± 4.0 N, and the mean net force was 262.4 ± 33.4 N. The mean location in the stroke cycle for minimum and maximum net force production was at 45% (insweep phase) and 75% (upsweep phase) of the stroke, respectively. This force–time profile also identified any stroke asymmetry.     

Stroke-coordination and symmetry of elite backstroke swimmers using a comparison between net drag force and timing protocols

Abstract

Stroke-coordination and symmetry influence the force fluctuations within any net drag force profile. The aim of this study was to analyse elite (FINA points 938) backstroke swimmers stroke-coordination using an instantaneous net drag force and timing protocols using a symmetry index tool. Ten male and nine female elite backstroke swimmers completed three maximum speed trials and five maximum speed net drag force swimming trials. Net drag force was measured using an assisted motorised dynamometer device. Each trial was filmed using three genlocked 50 Hz cameras, synchronised to the net drag force output from the force-platform. This methodology enabled the comparison of stroke-coordination timing symmetry index to net drag force symmetry index. The timing symmetry index and net drag force symmetry index yielded different results, the timing reflects the stroke-coordination, whilst the force index identified the effectiveness of the stroke. The only variable that was significantly different when comparing left and right stroke patterns was the location of minimum net drag forces. Conversely, gender influenced the location of maximum net drag force. Relationship analysis identified that location of maximum net drag force production was the only variable to correlate with speed within this cohort. Backstroke arm coordination was minimally influenced by gender.     

被动阻力变化对大学生初学游泳能力的影响研究

在游泳教学中,如何用量化的指标来科学地评判游泳者的游泳能力一直是游泳学界研究的热点。本文通过检测游泳能力掌握程度的不同对人体水中俯卧滑行能力的影响,讨论不同游泳能力者俯卧滑行能力的差异,反映游泳熟练程度对被动阻力的影响,来检验俯卧滑行能否作为评判游泳能力的强烈因子。选取华南师范大学体育专业38名身体健康的大学生按游泳能力的不同分为三组(平均年龄19岁,身高1.72cm,体重64.23kg)作为实验对象分别测量俯卧滑行的距离。要求实验对象采用双手置于头前蹬边滑行的方式进行测试,以手到池边的距离为测量距离。采用单因素方差分析检验俯卧滑行距离是否存在组间差异。结果表明,游泳能力会影响俯卧滑行距离(被动阻力)。不同水平游泳者其俯卧滑行的距离在统计学中有显著性差异,说明俯卧滑行能力可以作为评判游泳能力的强烈因子。     

Modelling the relationship between biomechanics and performance of young sprinting swimmers

The aim of this study was to compute a swimming performance confirmatory model based on biomechanical parameters. The sample included 100 young swimmers (overall: 12.3?±?0.74 years; 49 boys: 12.5?±?0.76 years; 51 girls: 12.2?±?0.71 years; both genders in Tanner stages 1–2 by self-report) participating on a regular basis in regional and national-level events. The 100?m freestyle event was chosen as the performance indicator. Anthropometric (arm span), strength (throwing velocity), power output (power to overcome drag), kinematic (swimming velocity) and efficiency (propelling efficiency) parameters were measured and included in the model. The path-flow analysis procedure was used to design and compute the model. The anthropometric parameter (arm span) was excluded in the final model, increasing its goodness-of-fit. The final model included the throw velocity, power output, swimming velocity and propelling efficiency. All links were significant between the parameters included, but the throw velocity–power output. The final model was explained by 69% presenting a reasonable adjustment (model's goodness-of-fit; x²/df?=?3.89). This model shows that strength and power output parameters do play a mediator and meaningful role in the young swimmers’ performance.     

Optimizing kick rate and amplitude for Paralympic swimmers via net force measures

Kicking is a key component of freestyle swimming yet the optimum combination of kick rate and kick amplitude remains unknown. For Paralympic swimmers, with upper and lower limb disabilities, the influence of the kick plays an important role in net force production. To determine optimum kick characteristics, 12 Paralympic swimmers aged 19.8 ± 2.9 years (mean ± s) were towed at their individual peak freestyle speed. The experimental conditions were (i) a prone streamline glide for passive trials and (ii) maximal freestyle kicking in a prone streamline for active trials at different speeds and kick amplitudes. Kick rate was quantified using inertial sensor technology. Towing speed was assessed using a novel and validated dynamometer, and net force was assessed using a Kistler force-platform system. When peak speed was increased by 5%, the active force increased 24.2 ± 5.3% (90% confidence limits), while kick rate remained at approximately 150 kicks per minute. Larger amplitude kicking increased the net active force by 25.1 ± 10.6%, although kick rate decreased substantially by 13.6 ± 5.1%. Based on the current kick rate and amplitude profile adopted by Paralympic swimmers, these characteristics are appropriate for optimizing net force.     

Unsteady flow phenomena in human undulatory swimming: a numerical approach

The undulatory underwater sequence is one of the most important phases in competitive swimming. An understanding of the recurrent vortex dynamics around the human body and their generation could therefore be used to improve swimming techniques. In order to produce a dynamic model, we applied human joint kinematics to three-dimensional (3D) body scans of a female swimmer. The flow around this dynamic model was then calculated using computational fluid dynamics with the aid of moving 3D meshes. Evaluation of the numerical results delivered by the various motion cycles identified characteristic vortex structures for each of the cycles, which exhibited increasing intensity and drag influence. At maximum thrust, drag forces appear to be 12 times higher than those of a passive gliding swimmer. As far as we know, this is the first disclosure of vortex rings merging into vortex tubes in the wake after vortex recapturing. All unsteady structures were visualized using a modified Q-criterion also incorporated into our methods. At the very least, our approach is likely to be suited to further studies examining swimmers engaging in undulatory swimming during training or competition.     

优秀自由泳运动员分段时间的特征研究

对近4届世界游泳锦标赛上高水平(决赛和半决赛)自由泳运动员的运动成绩进行分析,其中男、女各224人共历时7年.通过各分段时间与最终成绩的相关分析,以及历届不同水平、性别的优秀运动员在各个项目上的分段时间进行研究.结果发现,在任何项目上,不论水平高低,自由泳运动员都呈现较为类似的时间分配模式,其中在短距离项目上,水平越高的运动员前后半程的分段时间差越小并趋于均衡;在中距离项目上,男子运动员后半程保持速度的能力优于女子,历届世锦赛的获胜者在每个分段上处于领先位置,尤其在途中的游速上;同时长距离项目上水平较高的运动员在途中的分段时间有明显的下降趋势(加速)且变化较小,而水平稍差的运动员有明显的上升趋势(减速).建议教练员和运动员在保持总分段时间分配特征的前提下,通过技术优化和力量训练来提高分段成绩,进一步提高比赛成绩.     

The relative age effect among elite youth competitive swimmers

Abstract

The aim of this study was to analyse the relative age effect (RAE) in competitive swimming. The best 50 Portuguese swimmers (12- to 18-year-olds) for the main individual swimming pool events of both genders were considered. Analysis was conducted on 7813 swimming event participants, taking account of respective swimmer birth dates and the Fédération Internationale de Natation points gained. Differences in the distribution of birth dates by quarter year were determined using the Chi-square. A one-way analysis of variance ANOVA was used to test for differences measured in points between individuals by quarterly birth year intervals. A two-way analysis of variance ANOVA was also conducted to test the interaction between gender and seasonal birth date with regard to performance. The results show an inequitable distribution (p<0.01) of birth dates by quarter for almost all age groups and both genders. However, the distribution of birth dates by quarter for each considered swim event shows that RAE seems to exist only for 12-year-old females and 12- to 15-year-old males. Analysing mean swimming performance, post-hoc results (p<0.01) show no consistency in RAE. Higher performance occurs among older swimmers only in 100 m butterfly (female 1998, 1st≠2nd quarter, p=0.003). The results also show no interaction between gender and seasonal birth date (p<0.01). Findings of this study show that a higher number of swimmers, particular males, are born in the first two quarters of the year, although there is mostly no effect of seasonal birth date on performance differences within the top 50 swimmers.