KINETICS AND KINEMATICS OF THE BLOCK PHASE OF ELITE PARA SWIMMING STARTS

The present study presents a preliminary overview of dive start performance variables of the block and entry phase of elite para swimmers measured using the Kistler Performance Analysis Swimming System. Insight is given into the variability of these measures. These results can be used as a reference when examining the start phase in training

El efecto de la posición de partida en la salida de espalda en natación

Las salidas en natación suponen, cada vez más, un componente muy importante del tiempo final de prueba. Los problemas que plantea la investigación de la salida de espalda, debido a que parte del movimiento sucede dentro del agua y parte fuera, ha hecho que no aparezcan estudios previos que aporten luz a las dudas que plantean los entrenadores y los libros de texto sobre el tema. Uno de estos interrogantes es saber si la posición de partida de las piernas debe ser más o menos abierta (ángulos de la rodilla de 15±5º ó 90±5º). Para ello cuatro nadadores experimentados (21.5 ± 0.5 años, 59.3 ± 1.4 seg en 100m espalda y 27.2 ± 0.5 seg en 50m) fueron entrenados durante cuatro semanas en ambas salidas y efectuaron un total de tres salidas de cada, para posteriormente ser elegidas las mejores de cada uno, para cada condición del estudio. Se realizo un test de Wilcoxon para comparación de muestras relacionadas no paramétricas. En contra de lo que podía ser esperado no se encontraron diferencias significativas entre los tiempos a 5, 10 y 15 metros en ninguna de ellas (p=1, p=0.8 y p=0.6), así como en velocidades del centro de gravedad en salida y entrada (p=0.095 y p= 0.145), altura del centro de gravedad (p= 0.5), o longitud del vuelo (p=0.214) entre otras. Las similitudes del movimiento con el de un salto vertical sin contramovimiento, salvando la diferencia de la gravedad, nos hacen pensar que otras variables no controladas como el ángulo de la cadera o factores coordinativos relacionados con la acción de los músculos biarticulares puedan tener una influencia mayor que la variable estudiada. No obstante, los datos no paramétricos nos hacen ser prudentes y esperar a los resultados del análisis del resto de sujetos. Por último, decir que los nadadores usaban una de las dos variables normalmente, encontrándose más cómodos con ella. Esto nos lleva a sugerir a nivel técnico el trabajo de ambas en edades tempranas para posteriormente ver cual produce los mejores resultados.Peer Reviewe

USING UNDERWATER 3D KINEMATICS TO IMPROVE THE PARALYMPIC SWIMMING CLASSIFICATION SYSTEM

Swimming is a fundamental sport at the Olympic and Paralympic games, with the Paralympic classification system being the key difference between these games. To improve the accuracy of the classification system this case study investigated differences in the underwater hand kinematics of the affected and unaffected limb of an elite Para swimmer with hemiplegic cerebral palsy. In this case study, hemiplegic cerebral palsy caused impairments in strength, motor coordination and range of motion that affected hand speeds and trajectory paths during the underwater stroke phases. This work illustrates the benefit of using objective impairment and sport-specific measurements to gain insights into the impact that health conditions have on performance to guide Para swimming classification. This biomechanical analysis lays the foundations for the future improvement in international Para classification system

Improving the objectivity of the current World Para Swimming motor coordination test for swimmers with hypertonia, ataxia and athetosis using measures of movement smoothness, rhythm and accuracy

The current protocol for classifying Para swimmers with hypertonia, ataxia and athetosis involves a physical assessment where the individual’s ability to coordinate their limbs is scored by subjective clinical judgment. The lack of objective measurement renders the current test unsuitable for evidence-based classification. This study evaluated a revised version of the Para swimming assessment for motor coordination, incorporating practical, objective measures of movement smoothness, rhythm error and accuracy. Nineteen Para athletes with hypertonia and 19 non-disabled participants performed 30 s trials of bilateral alternating shoulder flexion-extension at 30 bpm and 120 bpm. Accelerometry was used to quantify movement smoothness; rhythm error and accuracy were obtained from video. Para athletes presented significantly less smooth movement and higher rhythm error than the non-disabled participants (p < 0.05). Random forest algorithm successfully classified 89% of participants with hypertonia during out-of-bag predictions. The most important predictors in classifying participants were movement smoothness at both movement speeds, and rhythm error at 120 bpm. Our results suggest objective measures of movement smoothness and rhythm error included in the current motor coordination test protocols can be used to infer impairment in Para swimmers with hypertonia. Further research is merited to establish the relationship of these measures with swimming performance

Maximal fully-tethered swim performance in Para swimmers with physical impairment

The assessment of swimming propulsion should be a cornerstone of Paralympic swimming classification. However, current methods do not objectively account for this component. This study evaluated the swimming propulsion of swimmers with and without physical impairment using a 30 s maximal fully-tethered freestyle swim test. Methods: Tethered forces were recorded during maximal fully-tethered swimming in eighty competitive swimmers with (n = 70) and without (n = 10) physical impairment. The relationships between absolute and normalised tether forces and maximal freestyle swim speed were established using general additive models. Results: Para swimmers with physical impairment had lower absolute and normalised tether forces than able-bodied swimmers, and there were moderate positive correlations found between tether forces and sport class (τ = .52 to .55, p < .001). There was a nonlinear relationship between tether force measures and maximal freestyle swim speed in the participant cohort (adj. R2 = .78 to .80, p < .001). Para swimmers with limb deficiency showed stronger relationships between tether force measures and maximal freestyle swim speed (adj. R2 = .78 to .82, p < .001) than for Para swimmers with hypertonia (adj. R2 = .54 to .73, p < .001) and impaired muscle power (adj. R2 = .61 to .70, p < .001). Conclusions: Physical impairments impact on Para swimmers’ tether forces during maximal fully-tethered freestyle swimming, explaining a significant proportion of their activity limitation. It is recommended that maximal fully-tethered swimming be included in Paralympic swimming classification as an objective assessment of swimming propulsion

The impact of limb deficiency impairment on Para swimming performance

Swimmers with limb deficiency are a core population within Para Swimming, accordingly this study examined the contribution of limb segments to race performance in these swimmers. Data were obtained for 174 male Para swimmers with limb deficiency. Ensemble partial least squares regression showed accurate predictions when using relative limb segment lengths to estimate Para swimmers’ personal best race performances. The contribution of limb segments to performance in swim events was estimated using these regression models. The analysis found swim stroke and event distance to influence the contributions of limb segments to performance. For freestyle swim events, these changes were primarily due to the increased importance of the hand, and decreased importance of the foot and shank, as the distance of the event increased. When comparing swim strokes, higher importance of the thigh and shank in the 100 m breaststroke compared with other swim strokes confirms the separate SB class. Varied contributions of the hand, upper arm and foot suggest that freestyle could also be separated from backstroke and butterfly events to promote fairer classification. This study shows that swim stroke and event distance influence the activity limitation of Para swimmers with limb deficiency suggesting classification should account for these factors

Reliability of the Elliptical Zone Method of Estimating Body Segment Parameters of Swimmers

Due to the difficulty of measuring forces and torques acting on a swimmer during mid-pool swimming, an inverse dynamics approach is required. Personalised body segment parameter (BSP) data enabling calculation of net forces and torques can be obtained using the elliptical zone method. The purpose of this study was to establish the reliability of estimating BSP data of swimmers by the elliptical zone method with segment outlines being traced manually on a personal computer screen. Five assessors digitised the segment landmarks and traced the body segments from front and side view digital photographs of 11 single arm amputee swimmers. Each swimmer was assessed five times by each of the five assessors. The order was fully randomised. Within assessor variability was less than 5% for the segment centre of mass position of all segments, for segment length except the neck (5.2%), and for segment mass except neck (11.9%), hands (Left: 8.1%; Right: 5.8%) and feet (Left: 7.3%; Right: 7.3%). Analysis of mean variability within and between assessors indicated that between assessor variability was generally as large or larger than within assessor variability. Consequently it is recommended that when seeking personalised BSP data to maximise the accuracy of derived kinetics and sensitivity for longitudinal and bilateral within-subject comparisons the individual should be assessed by the same assessor with mean values obtained from five repeat digitisations. This study established that using the elliptical zone method using E-Zone software is a reliable and convenient way of obtaining personalised BSP data for use in analysis of swimming

FISHnet: Learning to Segment the Silhouettes of Swimmers

We present a novel silhouette extraction algorithm designed for the binary segmentation of swimmers underwater. The intended use of this algorithm is within a 2D-to-3D pipeline for the markerless motion capture of swimmers, a task which has not been achieved satisfactorily, partly due to the absence of silhouette extraction methods that work well on images of swimmers. Our algorithm, FISHnet, was trained on the novel Scylla dataset, which contains 3,100 images (and corresponding hand-traced silhouettes) of swimmers underwater, and achieved a dice score of 0.9712 on its test data. Our algorithm uses a U-Net-like architecture and VGG16 as a backbone. It introduces two novel modules: a modified version of the Semantic Embedding Branch module from ExFuse, which increases the complexity of the features learned by the layers of the encoder; and the Spatial Resolution Enhancer module, which increases the spatial resolution of the features of the decoder before they are skip connected with the features of the encoder. The contribution of these two modules to the performance of our network was marginal, and we attribute this result to the lack of data on which our network was trained. Nevertheless, our model outperformed state-of-the-art silhouette extraction algorithms (namely DeepLabv3+) on Scylla, and it is the first algorithm developed specifically for the task of accurately segmenting the silhouettes of swimmers