Strength Level of Professional Elite Soccer Players after the COVID-19 Lockdown Period: A Retrospective Double-Arm Cohort Study.

BACKGROUND: It is well known that periods of inactivity generate a loss of muscle strength, a fundamental component of sports performance in soccer. However, little information is available on the decrease in strength levels in professional soccer players after the quarantine lockdown that occurred during the COVID-19 pandemic. AIM: To compare the isokinetic peak torque profiles of professional soccer players from different teams before and after the quarantine period generated by COVID-19. METHODS: A retrospective observational study was performed using data collected from two different professional elite-level soccer teams just before and immediately after the COVID-19 quarantine period. One team gave individual instructions to its players for conditioning maintenance at home during the quarantine period, while the other team used regular video calls to maintain the player's conditioning status on home training. The main outcomes were the mean peak torque of knee extensors and flexors, from concentric and eccentric contractions of each playing position. Analysis. A two-way ANOVA analysis was used to compare peak torque before and after the quarantine period and between both teams' strategies, showing a statistically significant reduction in eccentric knee flexor peak torque from the team that did not have remote monitoring. CONCLUSIONS: Remote monitoring programs are recommended so that athletes are less affected by the deleterious effects of confinement.

Association between Concentric and Eccentric Isokinetic Torque and Unilateral Countermovement Jump Variables in Professional Soccer Players.

Isokinetic tests have been highly valuable to athletic analysis, but their cost and technical operation turn them inaccessible. The purpose of this study was to verify the correlation between unilateral countermovement jump variables and isokinetic data. Thirty-two male professional soccer players were subjected to the isokinetic testing of both knee extensors and flexors in concentric and eccentric muscle contractions. They also executed unilateral countermovement vertical jumps (UCMJ) to compare maximum height, ground reaction force, and impulse power with isokinetic peak torque. Data analysis was conducted through Pearson correlation and linear regression. A high correlation was found between dominant unilateral extensor concentric peak torque and the UCMJ maximum height of the dominant leg. The non-dominant leg jump showed a moderate correlation. No other variable showed statistical significance. Linear regression allowed the generation of two formulae to estimate the peak torque from UCMJ for dominant and non-dominant legs. Although few studies were found to compare our results, leading to more studies being needed, a better understanding of the unilateral countermovement jump may be used in the future as a substitute to the expensive and technically demanding isokinetic testing when it is unavailable, allowing the assessment of lower limb physical asymmetries in athletic or rehabilitation environments.

Strength development according with age and position: a 10-year study of 570 soccer players.

BACKGROUND/AIM: The purpose of this study was to compare the isokinetic peak torque profiles from the quadriceps and hamstrings muscles during concentric and eccentric contractions in elite Brazilian soccer players across different field positions and age categories. Our hypothesis was that soccer players from different field positions are subjected to different ageing-related effects on their isokinetic peak torque. METHODS: This is a retrospective study based on professional elite-level soccer players between the years 2009 and 2019. It included 570 adult males who played for at least 5 years on first or second Brazilian divisions. Playing positions were divided as: goalkeepers, defenders, sidebacks, midfielders and forwards. Age categories were also divided as: G1 (17-20 years old), G2 (21-24 years old), G3 (25-28 years old), G4 (29-32 years old) and G5 (33 years old or more). RESULTS: The results indicate a moderate effect of age (F(4545)=8.197; p<0.001; η2=0.057) and a small effect of playing position (F(4545)=2.993; p<0.05; η2=0.021) on torque of concentric extensors; mainly from midfielders and goalkeepers with 29 years or more. CONCLUSIONS: Soccer players from different field positions are subjected to different ageing related effects on their muscular performance during their career special attention should be given to these players to avoid reduction in physical performance.

Concentric and eccentric isokinetic hamstring injury risk among 582 professional elite soccer players: a 10-years retrospective cohort study.

BACKGROUND/AIM: Different authors have tried to correlate the peak isokinetic torque values with the incidence of soccer match injuries. However, due to the wide variety of assessment testing protocols, such an inference becomes difficult. This study aimed to verify the capacity of an isokinetic test to establish injury risk reference values for hamstring strain injuries. METHODS: A retrospective cohort study based on isokinetic data and clinical records from the last 10 years was conducted in 582 Brazilian elite-professional soccer players, who were subjected to the same isokinetic test protocol, machine, and tester. A Multivariate Logistic Regression Analysis for Complex Data Sampling was used to generate injury risk statistical indexes. RESULTS: Multivariate regression analysis of both legs provided important data to identify the cut-off values of Concentric Peak Torque (181.82 Newton/*metres), Concentric Work (236.23 watts) and Concentric Power (130.11 joules). CONCLUSIONS: The injury risk indexes indicate that an increase of just one Newton unit in CPT (Concentric Peak Torque) and CJ (Concentric Power) above those cut-off values, can reduce the risk of future injuries by 2% and 2.7%, respectively.

Postural control analysis during a standardized kick task in soccer athletes / Análise do controle postural durante tarefa controlada do chute em atletas de futebol / Análisis del control postural durante tarea controlada del tiro en atletas de fútbol

ABSTRACT Introduction: Postural control is a determining factor for functional performance and motor skills during sports activities. Objective: The objective of this study was to investigate postural control during the controlled soccer ball kicking task through a biomechanical analysis system. Methods: The sample consisted of 11 professional male athletes recruited using convenience sampling, with a mean age of 22 years. The athletes performed twenty-five precision kicks at a target, with the ball in vertical motion released by means of a hand-held device synchronized with the computed biomechanical measurements. Marking of the lower limb segments involved in the kick and the ball were analyzed by accelerometry, while postural control measures were quantified by a force platform in three axes of movement. The support leg was investigated in single leg stance during all tests on the force platform. The main variables of postural control calculated by stabilographic analysis and computed during the 25 kicks were: center of pressure (COP) displacement area, velocity and frequency of COP oscillation in the anteroposterior and mediolateral directions. The mean was used for final analysis to determine the differences in the three phases: pre-kick, kick, and post-kick. Results: The results revealed significant differences (p <0.01) between the three phases, with the kick phase presenting higher values of postural COP oscillations than the other phases. The COP area and oscillation velocity were the variables with greatest sensitivity to changes in the kick phase, obtaining an effect size of d = 14 and d = 12, respectively. In clinical terms, the increase in COP values reached 557% between the pre-kick and kick phases; this difference was reduced to 241% when compared to post-kick (i.e., difference between kick and post-kick was 316%). Conclusion . These results have important implications for the perception of postural control responses during soccer ball kicks and consequently, for injury prevention when motor and sensory deficits are diagnosed in soccer players. Level of Evidence III; Study of nonconsecutive patients; without consistently applied reference ''gold'' standard.

RESUMO Introdução: O controle postural é um fator determinante para execução de gestos funcionais e desempenho motor durante as atividades esportivas. Objetivo: O objetivo deste estudo foi de investigar o controle postural durante a tarefa controlada do chute futebolístico por meio de um sistema de análise biomecânica. Métodos: A amostra foi constituída por 11 atletas profissionais do sexo masculino, recrutados por amostragem por conveniência, com média de idade de 22 anos. Os atletas realizaram vinte e cinco chutes de precisão em direção ao alvo, com a bola em movimento vertical lançada por meio de um dispositivo manual sincronizado com as medidas biomecânicas computadas. A marcação dos segmentos de membro inferior envolvidos no chute e a bola foram analisadas por meio da acelerometria, enquanto as medidas de controle postural foram quantificadas por meio de uma plataforma de força em três eixos do movimento. A perna de apoio foi investigada em apoio unipodal durante todos os testes sobre a plataforma de força. As principais variáveis de controle postural calculadas por uma análise estabilográfica e computadas durante os 25 chutes foram área de deslocamento do centro de pressão (COP), velocidade e frequência de oscilação do COP na direção anteroposterior e médio-lateral. A média foi utilizada para análise final para determinar as diferenças nas três fases: pré-chute, chute e pós-chute. Resultados: Os resultados revelaram diferenças significantes (p < 0,01) entre as três fases, sendo que a fase do chute apresentou valores maiores de oscilações posturais do COP do que as demais fases. A área e a velocidade de oscilação do COP foram as variáveis com maior sensibilidade às mudanças na fase do chute, obtendo magnitude de efeito em d = 14 e d = 12, respectivamente. Clinicamente, o aumento foi de 557% entre as fases pré-chute e chute; essa diferença foi reduzida para 241% na comparação com o pós-chute (ou seja, a diferença entre chute e pós-chute foi de 316%). Conclusões: Esses resultados têm implicações importantes para o reconhecimento das respostas de controle postural durante o chute futebolístico e, consequentemente, para prevenção de lesões quando déficits sensório-motores são diagnosticados em atletas de futebol. Nível de Evidência III; Estudo de pacientes não consecutivos; sem padrão de referência "ouro" aplicado uniformemente.

RESUMEN Introducción . El control postural es un factor determinante para la ejecución de gestos funcionales y desempeño motor durante las actividades deportivas. Objetivo: El objetivo de este estudio fue investigar el control postural durante la tarea controlada del tiro futbolístico por medio de un sistema de análisis biomecánico. Métodos: La muestra fue constituida por 11 atletas profesionales del sexo masculino reclutados por muestreo por conveniencia y con promedio de edad de 22 años. Los atletas realizaron veinticinco disparos de precisión en dirección al objetivo, con la pelota en movimiento vertical lanzada por medio de un dispositivo manual sincronizado con las medidas biomecánicas computadas. La marcación de los segmentos de la extremidad inferior involucrados en el tiro y la pelota fueron analizadas mediante acelerometría, mientras que las medidas de control postural fueron cuantificadas por medio de una plataforma de fuerza en tres ejes del movimiento. La pierna de apoyo fue investigada en apoyo unipodal durante todas las pruebas sobre la plataforma de fuerza. Las principales variables de control postural calculadas por un análisis estabilográfico y computadas durante los 25 disparos fueron área de desplazamiento del centro de presión (COP), velocidad y frecuencia de oscilación del COP en la dirección anteroposterior y medio-lateral. El promedio fue utilizado para análisis final para determinar las diferencias en las tres fases: pre-disparo, disparo, y post-disparo. Resultados: Los resultados revelaron diferencias significativas (p < 0,01) entre las tres fases, siendo que la fase del disparo presentó valores mayores de oscilaciones posturales del COP que las demás fases. El área y la velocidad de oscilación del COP fueron las variables con mayor sensibilidad a los cambios en la fase del disparo, obteniendo magnitud de efecto en d = 14 y d = 12, respectivamente. Clínicamente, el aumento fue del 557% entre las fases pre-disparo y disparo; esta diferencia se redujo al 241% en comparación con la fase post-disparo (es decir, la diferencia entre disparo y post-disparo fue de 316%). Conclusiones: Estos resultados tienen implicaciones importantes para el reconocimiento de las respuestas de control postural durante el tiro futbolístico y consecuentemente, para prevención de lesiones cuando se diagnostica déficit sensorio-motor en atletas de fútbol. Nivel de Evidencia III; Estudio de pacientes no consecutivos; sin patrón de referencia "oro" aplicado uniformemente.