Exploring Coaches' Cognitive Perception of Football Training Tasks: A Questionnaire-Based Study and Comparison with a Framework Tool for Assessing Cognitive Demands in Small-Sided Games / Exploración de la percepción cognitiva de los entrenadores sobre las tareas de entrenamiento de fútbol: un estudio basado en cuestionarios y una comparación con una herramienta marco para evaluar las demandas cognitivas en juegos reducidos / Exploração da perceção cognitiva de tarefas de treino em futebol: Estudo baseado numquestionário e comparação com uma ferramenta para avaliar e comparar as exigências cognitivas em jogos reduzidos

La función cognitiva es crucial en entornos de rendimiento competitivo debido al tipo de tareas y carga de trabajo involucradas. Sin embargo, aún se necesita determinar cómo toda la información ambiental en un entorno competitivo afecta la carga cognitiva.Por lo tanto, el objetivo fue investigar la percepción cognitiva de los entrenadores sobre las tareas de entrenamiento de fútbol, mediante el uso de un cuestionario y comparar los resultados con una herramienta de marco para evaluar las demandascognitivas en juegos reducidos. Un total de 57 entrenadores de fútbol (a nivel nacional y regional) completaron un cuestionario para calificar las demandas cognitivas percibidas de doce situaciones diferentes de juegos en espacios reducidos. Las respuestas fueron hechas por cada entrenador a partir de un conjunto de alternativas proporcionadas por los autores utilizando una escala de uso de Likert de 10 puntos. La carga cognitiva durante los juegos reducidos se calculó mediante una ecuación que incluía el número de jugadores implicados en la tarea, la superficie ocupada por cada jugador y la duración del ejercicio. Los resultados del cuestionario mostraron que los entrenadores de nivel nacional presentaron resultados de correlación más altos, mostrando una alta concordancia entre la percepción de los entrenadores y los resultados de la carga cognitiva en comparación con los entrenadores de nivel regional. La relación establecida entre todas las variables mostró que la complejidad de las tareas aumenta utilizando formatos con mayor número de jugadores, áreas pequeñas y ejercicios de mayor duración. Por lo tanto, el marco de carga cognitiva puede ser una herramienta útil y sencilla para quelos entrenadores evalúen las demandas cognitivas durante las sesiones de entrenamiento.(AU)

Cognitive function is crucial in competitive performance environments due to the type of tasks and workload involved. Thus, the present study aimed to investigate coaches’ cognitive perception of football training tasks, through the use of a questionnaire and compare the results with a framework tool to assess cognitive demands in small-sided games. A total of 57 football coaches (national and regional levels) filled out a questionnaire to rate the perceived cognitive demands of twelve different small-sidedgame situations. The answers were made by each coach from a set of alternatives supplied by the authors using a 10-point Likert use scale. The cognitive load during small-sided games was calculated using an equation that included the number of players involved in the task, the surface area occupied by eachplayer, and the duration of the exercise. The questionnaire results have shown that national-level coaches presented higher correlation results showing a high agreement between coaches' perception and the cognitive load results when compared to regional-level coaches. The relationship established between all variables showed that the complexity of tasks increases using formats with a larger number of players, small areas, and bigger duration drills. Thus, the cognitive load framework may be a useful and simple tool to coaches assess the cognitive demands during training sessions.(AU)

A função cognitiva é crucial em ambientes de desempenho competitivo devido ao tipo de tarefas e carga de trabalho envolvidas. No entanto, ainda precisa ser determinado como todas as informações ambientais em em contexto competitivo afetam a carga cognitiva. Assim, o objetivo deste estudofoi investigar a perceção cognitiva de treinadores sobre tarefas de treino de futebol, através de um questionário e comparando os resultados com um instrumento para avaliar as exigências cognitivas durante jogos reduzidos.Um total de 57 treinadores de futebol (nível nacional e regional) preencheram um questionário para avaliar as exigências cognitivas de doze situações diferentes jogos-reduzido. As respostas foram dadas por cada treinador a partir de um conjunto de alternativas fornecidas pelos autores utilizando uma escala de Likert de 10 pontos. A carga cognitiva durante pequenos jogos foi calculada através de uma equação queincluía o número de jogadores envolvidos na tarefa, a área de superfície ocupada por cada jogadore a duração do exercício. Os resultados do questionário mostraram que os treinadores de nível nacional apresentaram resultados de correlação mais elevados, mostrando uma alta concordância entre a perceção dos treinadores e os resultados de carga cognitiva em comparação com os treinadores de nível regional. A relação estabelecida entre todas as variáveis mostrou que a complexidade das tarefas aumenta utilizandoformatos com maior número de jogadores, áreas pequenas e exercícios de maior duração. Portanto, esta ferramenta para avaliar a carga cognitiva pode ser uma forma útil e simples para os treinadores avaliarem as exigências cognitivas durante as sessões de treino.(AU)

Neuromechanics of finger hangs with arm lock-offs: analyzing joint moments and muscle activations to improve practice guidelines for climbing.

Introduction: Climbing imposes substantial demands on the upper limbs and understanding the mechanical loads experienced by the joints during climbing movements is crucial for injury prevention and optimizing training protocols. This study aimed to quantify and compare upper limb joint loads and muscle activations during isometric finger hanging exercises with different arm lock-off positions. Methods: Seventeen recreational climbers performed six finger dead hangs with arm lock-offs at 90° and 135° of elbow flexion, as well as arms fully extended. Upper limb joint moments were calculated using personalized models in OpenSim, based on three-dimensional motion capture data and forces measured on an instrumented hang board. Muscle activations of upper limb muscles were recorded with surface electromyography electrodes. Results: Results revealed that the shoulder exhibited higher flexion moments during arm lock-offs at 90° compared to full extension (p = 0.006). The adduction moment was higher at 135° and 90° compared to full extension (p < 0.001), as well as the rotation moments (p < 0.001). The elbows exhibited increasing flexion moments with the increase in the arm lock-off angle (p < 0.001). Muscle activations varied across conditions for biceps brachii (p < 0.001), trapezius (p < 0.001), and latissimus dorsi, except for the finger flexors (p = 0.15). Discussion: Our findings indicate that isometric finger dead hangs with arms fully extended are effective for training forearm force capacities while minimizing stress on the elbow and shoulder joints. These findings have important implications for injury prevention and optimizing training strategies in climbing.

Effectiveness of wearable technology to optimize youth soccer players' off-training behaviour and training responses: a parallel group randomized trial.

BACKGROUND: Although youth soccer players meet and exceed the weekly physical activity (PA) guidelines also exhibit high off-training sedentary behaviour (SB) levels. Recent evidence indicated that low PA preceding training leads to decreased PA intensity in soccer practice and that SB impairs sports performance and recovery. Thus, a parallel group randomized trial examined the effect of activity wristbands on young players' off-training PA and SB profiles; assessed the added value of wearable wristbands with PA warnings; and investigated whether manipulating off-training PA can affect the players' training responses. METHODS: Thirty-two adolescent soccer players (16.1 ± 0.9 years old) were monitored during weekdays for two weeks (interspersed with one week). Players were randomly assigned to a reminder to move (REM) and a non-reminder to move group (nREM). The REM wore an activity wristband (Fitbit Charge 2) with PA warnings in the last week of research, while the nREM wore identical monitors without PA feedback. Throughout the study, off-training PA was assessed using tri-axial accelerometers, and training responses were analysed using wearable inertial monitoring units. Gardner-Altman estimation plots and a Fisher's Exact Test of Independence estimated each group's off-training PA changes between the monitored weeks. Complementary, an analysis of covariance (ANCOVA) quantified the effect of Fitbit wristband configurations (with a reminder to move or without a reminder to move) on the off-training PA and soccer training external load variables. The independent variable group had two levels (REM and nREM). The off-training PA and training load values collected in the first week were introduced in the model as a covariate, the groups were designated fixed factors and the off-training PA and training load from the third week were the dependent variables. The team was also included as a covariate and the between-group differences post-intervention were adjusted for baseline and team. RESULTS: Interestingly, results showed that different wearable wristbands did not influence the players' off-training PA profiles (p > 0.05). Concomitantly, no differences were observed in training responses (p > 0.05). CONCLUSION: Findings emphasize the importance of health and youth sports organizations in developing newer approaches for promoting healthier lifestyles, beyond training practices, with potentially favourable implications for sports performance.

Ubiquitous Computing in Sports and Physical Activity-Recent Trends and Developments.

The use of small, interconnected and intelligent tools within the broad framework of pervasive computing for analysis and assessments in sport and physical activity is not a trend in itself but defines a way for information to be handled, processed and utilised: everywhere, at any time. The demand for objective data to support decision making prompted the adoption of wearables that evolve to fulfil the aims of assessing athletes and practitioners as closely as possible with their performance environments. In the present paper, we mention and discuss the advancements in ubiquitous computing in sports and physical activity in the past 5 years. Thus, recent developments in wearable sensors, cloud computing and artificial intelligence tools have been the pillars for a major change in the ways sport-related analyses are performed. The focus of our analysis is wearable technology, computer vision solutions for markerless tracking and their major contribution to the process of acquiring more representative data from uninhibited actions in realistic ecological conditions. We selected relevant literature on the applications of such approaches in various areas of sports and physical activity while outlining some limitations of the present-day data acquisition and data processing practices and the resulting sensors' functionalities, as well as the limitations to the data-driven informed decision making in the current technological and scientific framework. Finally, we hypothesise that a continuous merger of measurement, processing and analysis will lead to the development of more reliable models utilising the advantages of open computing and unrestricted data access and allow for the development of personalised-medicine-type approaches to sport training and performance.

Using Computer Vision to Track Facial Color Changes and Predict Heart Rate.

The current technological advances have pushed the quantification of exercise intensity to new era of physical exercise sciences. Monitoring physical exercise is essential in the process of planning, applying, and controlling loads for performance optimization and health. A lot of research studies applied various statistical approaches to estimate various physiological indices, to our knowledge, no studies found to investigate the relationship of facial color changes and increased exercise intensity. The aim of this study was to develop a non-contact method based on computer vision to determine the heart rate and, ultimately, the exercise intensity. The method was based on analyzing facial color changes during exercise by using RGB, HSV, YCbCr, Lab, and YUV color models. Nine university students participated in the study (mean age = 26.88 ± 6.01 years, mean weight = 72.56 ± 14.27 kg, mean height = 172.88 ± 12.04 cm, six males and three females, and all white Caucasian). The data analyses were carried out separately for each participant (personalized model) as well as all the participants at a time (universal model). The multiple auto regressions, and a multiple polynomial regression model were designed to predict maximum heart rate percentage (maxHR%) from each color models. The results were analyzed and evaluated using Root Mean Square Error (RMSE), F-values, and R-square. The multiple polynomial regression using all participants exhibits the best accuracy with RMSE of 6.75 (R-square = 0.78). Exercise prescription and monitoring can benefit from the use of these methods, for example, to optimize the process of online monitoring, without having the need to use any other instrumentation.

The diagonal positioning of the goals modifies the external training load and the tactical behaviour of young football players.

The aim of this study was to identify how positioning the goals in diagonal configurations on the pitch modifies the external training load and the tactical behaviour of young football players during small-sided games. Four teams of five outfield players and a goalkeeper played six small-sided games of five minutes' duration in three different scenarios: 1) Control: goals placed one in front of the other; 2) Right diagonal goals: goals placed in the right-hand corner of the offensive half-pitch; and 3) Left diagonal goals: goals placed in the left-hand corner of the offensive half-pitch. The positioning-derived data from each player were collected with 10-Hz GPS units and were used to compute external load and tactical variables. Regarding the external load variables, differences were mainly focused on distance covered while walking in defence and game pace (variability), with higher values for the diagonal scenarios. Also, the length/width ratios in offence and defence were most likely lower in diagonal scenarios. In conclusion, the results showed that players' adaptations to the environmental constraints of positioning the goals diagonally were the enhancement of the width team variable and the variability of the length.

Guardiola, Klopp, and Pochettino: The Purveyors of What? The Use of Passing Network Analysis to Identify and Compare Coaching Styles in Professional Football.

We applied social networks analysis to objectively discriminate and describe interpersonal interaction dynamics of players across different top-coaching styles. The aim was to compare metrics in the passing networks of Jürgen Klopp, Pep Guardiola, and Mauricio Pochettino across the UEFA Champions League seasons from 2017 to 2020. Data on completed passes from 92 games were gathered and average passing networks metrics were computed. We were not only able to find the foundations on which these elite coaches build the passing dynamics in their respective teams, but also to determine important differences that represent their particular coaching signatures. The local cluster coefficient was the only metric not significantly different between coaches. Still, we found higher average shortest-path length for Guardiola's network (mean ± std = 3.00 ± 0.45 a.u.) compared to Klopp's (2.80 ± 0.52 a.u., p = 0.04) and Pochettino's (2.70 ± 0.39 a.u., p = 0.01). Density was higher for Guardiola's (64.16 ± 20.27 a.u.) than for Pochettino's team (51.42 ± 17.28 a.u., p = 0.008). The largest eigenvalue for Guardiola's team (65.95 ± 16.79 a.u.) was higher than for Klopp's (47.06 ± 17.25 a.u., p < 0.001) and Pochettino's (42,62 ± 12.01 a.u., p < 0.001). Centrality dispersion was also higher for Guardiola (0.14 ± 0.02 a.u.) when compared to Klopp (0.12 ± 0.03 a.u., p = 0.008). The local cluster coefficient seems to build the foundation for passing work, however, cohesion characteristics among players in the three teams of the top coaches seems to characterize their own footprint regarding passing dynamics. Guardiola stands out by the high number of passes and the enhanced connection of the most important players in the network. Klopp and Pochettino showed important similarities, which are associated to preferences toward more flexibility of interpersonal linkages synergies.

Off-training physical activity and training responses as determinants of sleep quality in young soccer players.

This study aimed to quantify and assess the relationship of young soccer players' off-training physical activity (PA) and training responses on sleep quality. Eleven adolescent soccer players (13 ± 0.5 years old) were monitored during weekdays for four consecutive weeks, throughout soccer practice days. Off-training PA and sleep quality were assessed using 100 Hz tri-axial accelerometers and training responses analyzed using 20 Hz global positioning measurement units. A cluster analysis classified all cases into three different dimensions, (1) off-training PA, (2) training responses and (3) sleep quality. For each dimension, the most important variables for classifying the cases into clusters were sedentary PA and moderate-to-vigorous PA; total distance covered and impacts; and sleep onset latency and sleep fragmentation index, respectively. Afterwards, a correspondence analysis was used to identify whether off-training PA and training responses affected sleep quality. Results exposed that high to medium off-training PA combined with medium to high training responses may have decreased sleep quality. Conversely, no correspondence was observed between off-training PA and training responses, with higher sleep quality. This study emphasizes the importance of sports organizations adopting a holistic approach to youth soccer players' development, that appropriately considers the inter-relationship between lifestyle, performance and health-related information.

The Influence of Functional Flywheel Resistance Training on Movement Variability and Movement Velocity in Elite Rugby Players.

The aim of this study was to identify the changes in movement variability and movement velocity during a six-week training period using a resistance horizontal forward-backward task without (NOBALL) or with (BALL) the constraint of catching and throwing a rugby ball in the forward phase. Eleven elite male rugby union players (mean ± SD: age 25.5 ± 2.0 years, height 1.83 ± 0.06 m, body mass 95 ± 18 kg, rugby practice 14 ± 3 years) performed eight repetitions of NOBALL and BALL conditions once a week in a rotational flywheel device. Velocity was recorded by an attached rotary encoder while acceleration data were used to calculate sample entropy (SampEn), multiscale entropy, and the complexity index. SampEn showed no significant decrease for NOBALL (ES = -0.64 ± 1.02) and significant decrease for BALL (ES = -1.71 ± 1.16; p < 0.007) conditions. Additionally, movement velocity showed a significant increase for NOBALL (ES = 1.02 ± 1.05; p < 0.047) and significant increase for BALL (ES = 1.25 ± 1.08; p < 0.025) between weeks 1 and 6. The complexity index showed higher levels of complexity in the BALL condition, specifically in the first three weeks. Movement velocity and complex dynamics were adapted to the constraints of the task after a four-week training period. Entropy measures seem a promising processing signal technique to identify when these exercise tasks should be changed.

Short-term effects of adding 1-m wide to each side of the basketball court on youth players' performance / Efectos a corto plazo de aumentar 1-m de ancho a cada lado de la cancha de baloncesto en el rendimiento de los jóvenes jugadores / Efeitos a curto prazo de aumentar o campo de basquetebol 1-m para cada lado no rendimento de jovens jogadores de basquetebol

This study aimed to identify short-term effects in basketball players' physical responses, technical performance, and tactical behaviour when the court dimension is increased 1-m wide to each side. Fourteen youth players participated in 5 vs. 5 simulated basketball games, under two different conditions: regular court (28x15m) and wider court (28x17m, 1-m wider for each side). Besides the assessment of physical and technical indicators, positional data were also used to compute the following variables: distance to the nearest opponent, distance to the nearest teammate, stretch-index and distance between centroids. Results indicated that in the wider court condition, the dispersion of player's displacement trajectories during the offensive phase increased, which had slight repercussions on their physical responses and in the teams' playing patterns. Conversely, during the defensive phase, players tended to move within the regular spatial references, regardless of court width manipulation. Overall, this study emphasizes that short-term effects of changing the court dimensions are relatively negligible, suggesting that informational constraints might require longer time-scales to yield robust changes in players' performance

El propósito de este estudio fue identificar los efectos a corto plazo en las respuestas físicas, técnicas y tácticas de jóvenes jugadores de baloncesto cuando la dimensión de la cancha aumenta 1-m de ancho en cada lado. Catorce jugadores jóvenes participaron en juegos simulados de baloncesto de 5 vs. 5, en dos condiciones diferentes: cancha regular (28x15m) y cancha más amplia (28x17m, 1-m de ancho a cada lado). Además de la evaluación de los indicadores físicos y técnicos, también se utilizaron datos de posición para calcular las siguientes variables: distancia al oponente más cercano, distancia al compañero de equipo más cercano, coeficiente de dispersión del equipo y distancia entre los centroides de los equipos. Los resultados indicaron que, en la condición de cancha más amplia, la dispersión de las trayectorias de movimiento de los jugadores durante la fase ofensiva aumentó, lo que tuvo ligeras repercusiones en sus respuestas físicas y en los patrones de juego de los equipos. En contrapartida, durante la fase defensiva, los jugadores tienden a moverse dentro de las referencias espaciales regulares, independientemente de la manipulación del ancho de la cancha. En general, este estudio enfatiza que los efectos a corto plazo de cambiar las dimensiones de la cancha son relativamente ligeros, lo que sugiere que las restricciones informativas pueden requerir bastante más tiempo para producir cambios concretos en el rendimiento de los jugadores

Este estudo teve como objectivo identificar os efeitos a curto prazo na performance física, técnica e tática de jovens jogadores de basquetebol, quando a largura do campo é aumentada 1-m para cada lado. Catorze jovens jogadores participaram em jogos simulados de 5 vs. 5, em dois contextos distintos: campo regular (28x17m) e campo amplo (28x17m, 1-m mais largo para ambos os lados). Paralelamente à avaliação de indicadores físicos e técnicos, foram também recolhidos dados posicionais, com o intuito de calcular as seguintes variáveis: distância ao oponente mais próximo, distância ao companheiro de equipa mais próximo, coeficiente de dispersão da equipa e distancia entre os centroides das equipas. Os resultados demonstraram que no contexto de campo amplo, a dispersão das trajetórias de movimento dos jogadores aumentou durante a fase ofensiva, o que acarretou ligeiras repercussões nos perfis físicos e nos padrões de jogo das equipas. Em contrapartida, durante a fase defensiva, os jogadores tendem a mover-se dentro dos referenciais espaciais, independentemente da manipulação do tamanho do campo. No geral, este estudo realçou que os efeitos a curto prazo de alterar as dimensões do campo são pouco expressivos, o que sugere que os constrangimentos de informação podem requerer substancialmente mais tempo para produzir alterações concretas no rendimento dos jogadores

Extracting spatial-temporal features that describe a team match demands when considering the effects of the quality of opposition in elite football.

Spatiotemporal patterns of play can be extracted from competitive environments to design representative training tasks and underlying processes that sustain performance outcomes. To support this statement, the aims of this study were: (i) describe the collective behavioural patterns that relies upon the use of player positioning in interaction with teammates, opponents and ball positioning; (ii) and define the underlying structure among the variables through application of a factorial analysis. The sample comprised a total of 1,413 ball possession sequences, obtained from twelve elite football matches from one team (the team ended the season in the top-5 position). The dynamic position of the players (from both competing teams), as well as the ball, were captured and transformed to two-dimensional coordinates. Data included the ball possession sequences from six matches played against top opponents (TOP, the three teams classified in the first 3 places at the end of the season) and six matches against bottom opponents (BOTTOM, the three teams classified in the last 3 at the end of the season). The variables calculated for each ball possession were the following: ball position; team space in possession; game space (comprising the outfield players of both teams); position and space at the end of ball possession. Statistical comparisons were carried with magnitude-based decisions and null-hypothesis analysis and factor analysis to define the underlying structure among variables according to the considered contexts. Results showed that playing against TOP opponents, there was ~38 meters game length per ~43 meters game width with 12% of coefficient of variation (%). Ball possessions lasted for ~28 seconds and tended to end at ~83m of pitch length. Against BOTTOM opponents, a decrease in the game length with an increase in game width and in the deepest location was observed in comparison with playing against TOP opponents. The duration of ball possession increased considerable (~37 seconds), and the ball speed entropy was higher, suggesting lower levels of regularity in comparison with TOP opponents. The BOTTOM teams revealed a small EPS. The Principal Component Analysis showed a strong association of the ball speed, entropy of the ball speed and the coefficient of variation (%) of the ball speed. The EPS of the team in possession was well correlated with the game space, especially the game width facing TOP opponents. Against BOTTOM opponents, there was a strong association of ball possession duration, game width, distance covered by the ball, and length/width ratio of the ball movement. The overall approach carried out in this study may serve as the starting point to elaborate normative models of positioning behaviours measures to support the coaches' operating decisions.

Entropy Measures Can Add Novel Information to Reveal How Runners' Heart Rate and Speed Are Regulated by Different Environments.

Ecological psychology suggests performer-environment relationship is the appropriate scale for examining the relationship between perception, action and cognition. Developing performance requires variation in practice in order to design the attractor-fluctuation landscape. The present study aimed to identify the effects of varying levels of familiarity and sensorimotor stimuli within the environment in runners' speed and heart rate (HR) regularity degree, and short-term memory Twelve amateur runners accomplished three 45-min running trials in their usual route, in an unusual route, and an athletics 400-m track, wearing a GPS and an HR monitor. Sample entropy (SampEn) and complexity index (CI), over speed and HR, were calculated. Pre and post-trial, participants performed the Backward Digit Span task for cognitive assessment. Higher entropies were found for the 400-m track, compared to the usual and unusual routes. Usual routes increased speed SampEn (63% of chances), but decreased HR CI when compared to unusual routes (60% of chances). Runners showed higher overall short-term memory performance after unusual routes, when compared to usual routes (85% of chances), indicating positive relation to attentional control. The contexts of practice may contribute to change predictability from single to multiple timescales. Thus, by considering that time structuring issues can help diagnosing habituation of training routes, this study brings novel information to the long-term process of training.

Off-Training Levels of Physical Activity and Sedentary Behavior in Young Athletes: Preliminary Results during a Typical Week.

The level of physical activity (PA) and sedentary behavior (SED) off-training of young athletes may reveal the quality of recovery from training and highlight health related issues. Thus, the aim was to identify and describe young athletes' PA and SED off-training, according to daily life activities. Eight athletes (15.7 ± 2 years, 1.72 ± 0.6 m height, 62.9 ± 10.2 kg) of a sport talent program wore on their waist a tri-axial accelerometer (ActiGraph® wGT9X-link, Shalimar, FL, USA) at 30 Hz for 15 consecutive days, and reported their schedule. A two-step cluster analysis classified three groups according to sedentary PA and MVPA. The Sedentary (56.9%), presented the highest sedentary PA (mean [CI], 37.37 [36.45⁻38.29] min/hour); The Hazardous (19.4%) had the lowest values of sedentary and MVPA (10.07 [9.41⁻10.36] min/hour and 8.67 [7.64⁻9.70] min/hour, respectively). Balanced (23.7%) had the highest MVPA (28.61 [27.16⁻30.07] min/hour). Sedentary had the lowest count of home time associated (20%) and higher school (26%) time when compared to the Hazardous (13%). The Balanced showed the highest count of school (61%) and home time (47%). Different profiles for young athletes revealed alarming behavior in the associations with sedentary PA, sitting and SED breaks, which may influence performance and health.

Entropy measures detect increased movement variability in resistance training when elite rugby players use the ball.

OBJECTIVES: This study described the variability in acceleration during a resistance training task, performed in horizontal inertial flywheels without (NOBALL) or with the constraint of catching and throwing a rugby ball (BALL). DESIGN AND METHODS: Twelve elite rugby players (mean±SD: age 25.6±3.0years, height 1.82±0.07m, weight 94.0±9.9kg) performed a resistance training task in both conditions (NOBALL AND BALL). Players had five minutes of a standardized warm-up, followed by two series of six repetitions of both conditions: at the first three repetitions the intensity was progressively increased while the last three were performed at maximal voluntary effort. Thereafter, the participants performed two series of eight repetitions from each condition for two days and in a random order, with a minimum of 10min between series. The structure of variability was analysed using non-linear measures of entropy. RESULTS: Mean changes (%; ±90% CL) of 4.64; ±3.1g for mean acceleration and 39.48; ±36.63a.u. for sample entropy indicated likely and very likely increase when in BALL condition. Multiscale entropy also showed higher unpredictability of acceleration under the BALL condition, especially at higher time scales. CONCLUSIONS: The application of match specific constraints in resistance training for rugby players elicit different amount of variability of body acceleration across multiple physiological time scales. Understanding the non-linear process inherent to the manipulation of resistance training variables with constraints and its motor adaptations may help coaches and trainers to enhance the effectiveness of physical training and, ultimately, better understand and maximize sports performance.