BIOMECHANICAL FEATURES OF PERFORMANCE DOMINANCE IN THE LOWER LIMBS

INTRODUCTION: The kinematic, dynamic and myoelectrical characteristics of the one-foot vertical jump were examined for the dominant and the non-dominant foot, in order to determine the biomechanical features of performance dominance in the lower limbs. METHODS: Seventy-nine volunteers performed five vertical jumps with either foot on a piezoelectric force platform (Kistler). The sampling frequency was set at 1000 Hz. Three-dimensional analysis was employed for the determination of the kinematic characteristics of the movement, at a sampling rate of 60 Hz. The APAS system was used to record surface electromyograms of four muscles in the lower limb (sampling frequency 1000 Hz). The foot that achieved the highest performance was defined as the dominant foot. Correspondence analysis was employed for the evaluation of the data. RESULTS: The analysis of the data revealed that high performance scores were the output of a common movement pattern for both the dominant and the nondominant foot. Small values of the maximum angular velocity of the foot, leg and thigh were found during the supporting phase of the jump with either limb. The biceps femoris was highly activated before the contact of the foot, but presented less activity during the supporting phase of the jump. The activity of the biceps femoris before the supporting phase of the jump was greater when the jump was performed with the dominant foot. The vastus medialis of the dominant limb presented greater activity during the negative phase of the jump. Finally, the rectus femoris presented greater activity during the positive phase of the jump when the jump was executed with the dominant foot, while the activity of the gastrocnemius was less. CONCLUSION: The differences of the myoelectrical activity of the biceps femoris between the dominant and the non-dominant foot werprimarily responsible for the differences between the two feet in the height of the jump

BIOMECHANICAL ANALYSIS OF PERFORMANCE IMPROVEMENT IN AIMING MOTOR TASKS

INTRODUCTION: The improvement of performance is closely related to specific modifications of the kinematics and the myoelectrical parameters of each aiming motor skill. The purpose of this study was to determine the modifications of selected kinematic and myoelectrical parameters which resulted in the improvement of aiming performance. METHODS: Seventy volunteers practiced a novel throwing skill which involved the throw of a ball performing elbow flexion. Kinematics were computed through film analysis at 80Hz. Furthermore, the surface ectromyograms of four muscles in the elbow region were analyzed to determine the changes in the timing and the intensity of muscle activation which may be accounted for improved performance. The correspondence analysis was employed for the evaluation of the data. RESULTS: The results revealed that performance enhancement was related to the decrease in the time and the displacement of the movement. Practice also resulted to significant modifications in the electrical activity of the muscles. The number of the active muscles was diminished and the agonist activity was reduced. The antagonist activity was increased but it was presented significantly farther from the beginning of the movement after practice. CONCLUSION: Practice brought about specific modifications in the muscular contribution to the throwing task, by means of a reduction in the electrical activity of the primary antagonistic muscles during the movement. These modifications gave rise to specific alterations in the physical aspects of the skill, which directly resulted in improved performance

Front Crawl and Backstroke Sprint Swimming have Distinct Differences along with Similar Patterns Regarding Trunk Rotations

Background: Front crawl and backstroke share similar trunk rotating characteristics and tempt coaches to transfer teaching parts from one stroke to the other intuitively. However, the degree of similarity has yet to be determined. The coordination of the pelvis and the 7th cervical vertebrae (C7), during yaw and roll rotation, when sprint swimming front crawl, and backstroke was studied. Methods: Thirty-four swimmers were assessed on their performance in25m-sprint of each stroke. Using inertial sensors, each segment’s time series of angular displacement was calculated. Their amplitudes, mean autocorrelation values, max cross-correlation coefficient, phase lag, and relative power at the main frequency were analyzed. For all comparisons, the p-value was set to 0.05. Results: Pelvis yaw and roll and C7 roll amplitudes were greater at backstroke, C7 yaw was greater at front crawl. Autocorrelations ranged from 0.79 to 0.82 except for the pelvis at front crawl in yaw which was 0.72±0.16. Relative power at the main frequency ranged from 47% to 52% except for the yaw pelvis’ at the front crawl which was lower (32.81±14.09%). Backstroke had larger mean values in all cases and roll had larger mean values than yaw. Cross-correlation between the two segments yielded higher values at roll. At roll direction, the leading segment in the front crawl was the pelvis while in backstroke, it was the C7 which was true in all cases. In all cases, the coupling was slightly deviating from in-phase mode except from backstroke yaw which yield phase lag values of -13.35±1.14% of stroke cycle time. Conclusions: Although both strokes share similar characteristics their intersegmental coupling differs. The findings of the study imply that proper focus should be given to enhance only a positive transfer of learning between the two strokes

Analysis of upper limb propulsion in young swimmers in front-crawl through Statistical Parametric Mapping

This study aimed to: (i) verify the within-subject effect of the dominant and non-dominant upper limb propulsion during consecutive arm-pulls through discrete (average) and continuous analysis (SPM), and; (ii) compare young swimmers’ propulsion between both upper limbs through discrete (average) and continuous analysis (Statistical Parametric Mapping – SPM). The sample consisted of 17 young male swimmers (age = 16.02 ± 0.61-years) who regularly participate in national and international level competitions. A set of kinematic and propulsion variables were measured during a 25-m maximal trial in front-crawl. Statistical analysis of propulsion was performed using discrete variables and through SPM. Swimming velocity showed a significant decrease over time. A significant interaction between the “time” (consecutive arm-pulls) and “side” (dominant vs. non-dominant) effects was observed in both statistical analyzes. Only the dominant upper limb demonstrated a significant “time” effect with a significant difference (p < 0.05) between the first and third arm-pulls. SPM indicated that the “time” effect was observed between the ~ 34% and ~ 42% of the arm-pull. The differences between the first and third arm-pull were verified between the ~ 32% and ~ 43% of the arm-pull. A non-significant “side” effect was verified in both analyzes. Therefore, SPM analysis provided more sensitive and accurate outputs than discrete analysis. This will allow coaches to design specific training drills focused on specific moments of the arm-pullThis work is supported by national funds (FCT - Portuguese Foundation for Science and Technology) under the project UIDB/DTP/04045/2020info:eu-repo/semantics/publishedVersio

Gait analysis comparison between manual marking, 2D pose estimation algorithms, and 3D marker-based system

IntroductionRecent advances in Artificial Intelligence (AI) and Computer Vision (CV) have led to automated pose estimation algorithms using simple 2D videos. This has created the potential to perform kinematic measurements without the need for specialized, and often expensive, equipment. Even though there's a growing body of literature on the development and validation of such algorithms for practical use, they haven't been adopted by health professionals. As a result, manual video annotation tools remain pretty common. Part of the reason is that the pose estimation modules can be erratic, producing errors that are difficult to rectify. Because of that, health professionals prefer the use of tried and true methods despite the time and cost savings pose estimation can offer.MethodsIn this work, the gait cycle of a sample of the elderly population on a split-belt treadmill is examined. The Openpose (OP) and Mediapipe (MP) AI pose estimation algorithms are compared to joint kinematics from a marker-based 3D motion capture system (Vicon), as well as from a video annotation tool designed for biomechanics (Kinovea). Bland-Altman (B-A) graphs and Statistical Parametric Mapping (SPM) are used to identify regions of statistically significant difference.ResultsResults showed that pose estimation can achieve motion tracking comparable to marker-based systems but struggle to identify joints that exhibit small, but crucial motion.DiscussionJoints such as the ankle, can suffer from misidentification of their anatomical landmarks. Manual tools don't have that problem, but the user will introduce a static offset across the measurements. It is proposed that an AI-powered video annotation tool that allows the user to correct errors would bring the benefits of pose estimation to professionals at a low cost

Swimming coaches’ professional development and training practices: an international survey

This study investigated swim coaches' perceptions of professional development issues and current training practices according to their coaching experience, education level, and gender. An online survey (January—April 2022) was completed by 123 swim coaches (96 male/27 female) of competitive swimmers based in 41 countries. The survey consisted of 36 questions divided into six sections: (1) background information, (2) developing swim coaching through learning, (3) self-evaluation, (4) interpersonal-intrapersonal interactions, (5) life skills, and (6) analyzing swimming performance. Pearson chi-square assessed the relationship between the frequency of responses and professional background and gender. The survey results indicated that swim coaches' educational level is potentially one of the most influential parameters affecting the coaches' perceptions about their own professional development. The data presented may be used for the future design of coach education programmes as they advance current knowledge on understanding psycho-social issues related to professional development and training perceptions involved in the competitive swimming environment

Recovery kinetics of knee flexor and extensor strength after a football match

© 2015 The Authors. Published by PLOS. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.1371/journal.pone.0128072We examined the temporal changes of isokinetic strength performance of knee flexor (KF) and extensor (KE) strength after a football match. Players were randomly assigned to a control (N = 14, participated only in measurements and practices) or an experimental group (N = 20, participated also in a football match). Participants trained daily during the two days after the match. Match and training overload was monitored with GPS devices. Venous blood was sampled and muscle damage was assessed pre-match, post-match and at 12h, 36h and 60h post-match. Isometric strength as well as eccentric and concentric peak torque of knee flexors and extensors in both limbs (dominant and non-dominant) were measured on an isokinetic dynamometer at baseline and at 12h, 36h and 60h after the match. Functional (KFecc/KEcon) and conventional (KFcon/KEcon) ratios were then calculated. Only eccentric peak torque of knee flexors declined at 60h after the match in the control group. In the experimental group: a) isometric strength of knee extensors and knee flexors declined (P<0.05) at 12h (both limbs) and 36h (dominant limb only), b) eccentric and concentric peak torque of knee extensors and flexors declined (P<0.05) in both limbs for 36h at 60°/s and for 60h at 180°/s with eccentric peak torque of knee flexors demonstrating a greater (P<0.05) reduction than concentric peak torque, c) strength deterioration was greater (P<0.05) at 180°/s and in dominant limb, d) the functional ratio was more sensitive to match-induced fatigue demonstrating a more prolonged decline. Discriminant and regression analysis revealed that strength deterioration and recovery may be related to the amount of eccentric actions performed during the match and athletes' football-specific conditioning. Our data suggest that recovery kinetics of knee flexor and extensor strength after a football match demonstrate strength, limb and velocity specificity and may depend on match physical overload and players' physical conditioning level.Published versio

Physical activity in pre-school children: Trends over time and associations with body mass index and screen time

Background: Pre-school years are important for adopting health behaviours; however, today’s children seem to be overweight, present low physical activity (PA) levels and exceed screen time (ST) recommendations. Aim: To examine (a) time trends in PA in Greek pre-school children, (b) the associations among PA, body mass index (BMI) and ST and (c) potential PA differences between boys and girls. Subjects and methods: Data from five cross-sectional cohorts (2005 [n = 252]; 2008 [n = 212]; 2011 [n = 187]; 2014 [n = 194]; 2017 [n = 128]) were compared. PA was assessed using Omron HJ-720IT-E2 pedometers, whereas ST was reported by participants’ parents. A 4-way ANOVA was applied on children’s average week step counts. Results: A significant association (F = 828.90, p  2 hours/day). Conclusion: Effective interventions aiming at reducing ST and enhancing PA seem imperative if children’s health is to be safeguarded

Análisis de la efectividad de los elementos técnico-tácticos durante la fase de servicio-recepción en jóvenes atletas de tenis de mesa

The aim of the current study was to record and compare the technical and tactical elements of the strokes during serve, receive and winning shots between winning and defeated female table tennis athletes, belonging to the cadet leagues and to study their relation with the outcome of the match. The sample for this study was 36 official table tennis matches (2487 rallies) of cadets (14 ± 1.48 years). The technical and tactical analyses was concerned with the type and direction of the serve and receiving the ball, the success rates of the player serving and receiving, as well as the process of winning a point after an offensive shot. In order to record and analyze the matches, the method of video analysis was used and for the statistical treatment of the data the non-parametric X2 test was implemented. The results revealed that the forehand grip was mainly used for the execution of a serve and the serve of the young female winners was statistically superior to the losers, regarding the score and the rates of successfully receiving the ball. Statistically significant differences were also observed in the first return of the ball after the execution of the serve, where the winners preferred mostly the forehand-push, backhand-topspin and forehand-topspin, making even more winning shots compared to the losers. The findings of the current study could be used by coaches in Cadet Leagues to improve training methods and help them to provide feedback to the athletes during the matches.El objetivo de este estudio fue grabar y comparar los elementos técnicos y tácticos de los golpes en el servicio, la recepción y los golpes ganadores (winner shots) entre atletas de tenis de mesa mujeres ganadoras y derrotadas que pertenecen a ligas cadetes, y estudiar su relación con el resultado del partido. La muestra para este estudio fue de 36 partidos oficiales de tenis de mesa (2487 rallies) de cadetes (14 ± 1.48 años). Los análisis técnicos y tácticos estaban relacionados con el tipo y dirección del servicio y la recepción, las tasas de éxito de la jugadora al servir y recibir, así como el proceso de ganar un punto luego de un golpe ofensivo. Con el fin de grabar y analizar los partidos, se usó el método de análisis de video y para el tratamiento estadístico de los datos se usó la prueba no paramétrica X2. Los resultados revelaron que el agarre forehand era usado principalmente para la ejecución de un servicio, y el servicio de las mujeres ganadoras jóvenes fue estadísticamente superior al de las perdedoras en cuanto al puntaje y las tasas de recepción exitosa. También se observaron diferencias significativas estadísticamente en la primera devolución de la pelota luego de la ejecución del servicio, cuando las ganadoras prefirieron principalmente el forehand-push, el backhand-topspin y el forehand-topspin lograron más golpes ganadores comparadas con las perdedoras. Los hallazgos del presente estudio pueden ser útiles para los entrenadores en las ligas cadetes para que mejoren sus métodos de entrenamiento y puedan brindar una mejor retroalimentación a las atletas durante los partidos

Análisis de la efectividad de los elementos técnico-tácticos durante la fase de servicio-recepción en jóvenes atletas de tenis de mesa

The aim of the current study was to record and compare the technical and tactical elements of the strokes during serve, receive and winning shots between winning and defeated female table tennis athletes, belonging to the cadet leagues and to study their relation with the outcome of the match. The sample for this study was 36 official table tennis matches (2487 rallies) of cadets (14 ± 1.48 years). The technical and tactical analyses was concerned with the type and direction of the serve and receiving the ball, the success rates of the player serving and receiving, as well as the process of winning a point after an offensive shot. In order to record and analyze the matches, the method of video analysis was used and for the statistical treatment of the data the non-parametric X2 test was implemented. The results revealed that the forehand grip was mainly used for the execution of a serve and the serve of the young female winners was statistically superior to the losers, regarding the score and the rates of successfully receiving the ball. Statistically significant differences were also observed in the first return of the ball after the execution of the serve, where the winners preferred mostly the forehand-push, backhand-topspin and forehand-topspin, making even more winning shots compared to the losers. The findings of the current study could be used by coaches in Cadet Leagues to improve training methods and help them to provide feedback to the athletes during the matches.El objetivo de este estudio fue grabar y comparar los elementos técnicos y tácticos de los golpes en el servicio, la recepción y los golpes ganadores (winner shots) entre atletas de tenis de mesa mujeres ganadoras y derrotadas que pertenecen a ligas cadetes, y estudiar su relación con el resultado del partido. La muestra para este estudio fue de 36 partidos oficiales de tenis de mesa (2487 rallies) de cadetes (14 ± 1.48 años). Los análisis técnicos y tácticos estaban relacionados con el tipo y dirección del servicio y la recepción, las tasas de éxito de la jugadora al servir y recibir, así como el proceso de ganar un punto luego de un golpe ofensivo. Con el fin de grabar y analizar los partidos, se usó el método de análisis de video y para el tratamiento estadístico de los datos se usó la prueba no paramétrica X2. Los resultados revelaron que el agarre forehand era usado principalmente para la ejecución de un servicio, y el servicio de las mujeres ganadoras jóvenes fue estadísticamente superior al de las perdedoras en cuanto al puntaje y las tasas de recepción exitosa. También se observaron diferencias significativas estadísticamente en la primera devolución de la pelota luego de la ejecución del servicio, cuando las ganadoras prefirieron principalmente el forehand-push, el backhand-topspin y el forehand-topspin lograron más golpes ganadores comparadas con las perdedoras. Los hallazgos del presente estudio pueden ser útiles para los entrenadores en las ligas cadetes para que mejoren sus métodos de entrenamiento y puedan brindar una mejor retroalimentación a las atletas durante los partidos