Social jetlag (SJL), resulting from misalignment between biological rhythms and social schedules, has emerged as a prevalent phenomenon in modern society, particularly among young athletes. However, the effect of SJL on performance is poorly studied. Jump and dynamic balance are two key skills in volleyball, as the first allows the player to perform better both during the offense and defense phase, and the second is fundamental in landing and in injury prevention. Therefore, our aim was to investigate the effect of SJL on jump skill performance and balance in female volleyball players. Thirty female volleyball players (mean age: 17.3 ± 0.88 years) participated in the study. SJL was assessed using the Munich ChronoType Questionnaire (MCTQ), integrated with Jankowsky\'s sleep-corrected formula. Jump skill performance was evaluated using a standardized jump test, the Vertec Jump Test, while balance was assessed with the Y Balance Test. The tests were performed at 09:00 a.m. and at 06:00 p.m. The results revealed that players with greater SJL exhibited decreased jump performance, characterized by lower vertical jump height (p = 0.02). Furthermore, players with lower SJL showed the typical difference between morning and afternoon performance (p = 0.001), demonstrating their synchronization between biological rhythms and social commitments, while no statistically significant difference between the two sessions was shown in players with higher SJL. Regarding balance, no significant association with SJL was found, but the morning session yielded lower results than the afternoon one (p = 0.01). These findings highlight the detrimental impact of SJL on jump skill performance, underscoring the importance of optimizing sleep-wake schedules and circadian alignment to enhance athletic performance. Future research should explore targeted interventions, such as sleep hygiene education, to minimize social jetlag and promote optimal performance in adolescent athletes.

BACKGROUND: Anterior cruciate ligament (ACL) injuries may correlate with lower limb angles and biomechanical factors in both dominant and non-dominant legs at initial contact (IC) post-landing. This study aims to investigate the correlation between ankle angles in three axes at IC and knee and hip joint angles during post-spike landings in professional volleyball players, both pre- and post-fatigue induction.
OBJECTIVE: To what extent does fatigue influence lower limb joint angles, and what is the relationship between ankle joint angles and hip and knee angles at IC during the landing phase following a volleyball spike?
METHODS: Under conditions involving the peripheral fatiguing protocol, the lower limb joint angles at IC following post-spike landings were measured in 28 professional male volleyball players aged between 19 and 28 years, who executed the Bosco fatigue protocol both before and after inducing fatigue. A paired t-test was utilized to compare the joint angles pre- and post-fatigue in both dominant and non-dominant legs. Furthermore, Pearson\'s correlation test was conducted to explore the relationship between ankle angles at IC and the corresponding knee and hip joint angles.
RESULTS: The findings of the study revealed that fatigue significantly increased hip external rotation and decreased knee joint flexion and external rotation in both the dominant and non-dominant legs (p < 0.05). Additionally, correlation analysis demonstrated that the ankle joint\'s positioning in the frontal and horizontal planes was significantly associated with hip flexion and external rotation at the IC, as well as with knee flexion and rotation (0.40 < r < 0.80).
CONCLUSIONS: Fatigue increased hip external rotation and ankle internal rotation, weakening the correlation between these joints while strengthening the ankle-knee relationship, indicating a reduced hip control in jumps. This suggests a heightened ACL injury risk in the dominant leg due to the weakened ankle-hip connection, contrasting with the non-dominant leg.

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BACKGROUND: Anterior cruciate ligament injuries are serious conditions encountered in volleyball players and occur frequently during spike jump landings. During spike jumps, the lower limb kinematics and kinetics during landing may be altered in relation to the ball position.
OBJECTIVE: Does the ball position have an effect on lower-limb kinematics and kinetics during spike jumps?
METHODS: We measured the lower limb kinematics and kinetics of 20 healthy female college volleyball athletes during a spike jump using a three-dimensional motion analysis system. The ball positions were set to normal, dominant, and non-dominant positions. A repeated analysis of variance was used to compare the lower limb kinematics and kinetics at the initial contact and the maximum knee flexion during jump landing. Additionally, statistical parametric mapping analysis was used to analyze changes over time during the spike jumps.
RESULTS: At the initial contact of the spike jump landing, the knee valgus angle, trunk lateral bending angle, and maximum knee valgus moment when the ball was set at the non-dominant position increased compared to those at the dominant position. Statistical parametric mapping analysis showed no significant change in knee valgus angle and moment of jump landing.
CONCLUSIONS: Knee valgus angle, trunk lateral bending angle, and maximum knee valgus moment increased with the non-dominant position; furthermore, the risk of ACL injury may also be increased.
CONCLUSIONS: The posture at ball impact may influence the landing kinematics and kinetics. Therefore, it is necessary to pay close attention to movements during and prior to landing.

In elite volleyball, the serve takes an offensive form, aiming to directly score a point or significantly hinder the opponent from launching an attack. Which is why the research aimed to compare the type and effectiveness of the serve in the main round of Tauron and PlusLiga in the 2021/2022 season and update the current knowledge on the types of serves by function and gender. The study analysed observation consisted of 314 women\'s and men\'s matches. VolleyStation Pro v 1.29.5; Volleystation z o. o. Poland. Data from the main round matches that took place in the 2021/2022 season in the Polish elite league PlusLiga (182 men\'s matches) and Tauron Liga (132 women\'s matches) were used, and the regular season consisted of 2 rounds. The average percentage effectiveness of the serve in women was higher (E = 22%) than in men (E = 15%). In women, only 3 types were observed (JS, JF and W), as much as 86% of all the serves were JF serves. In men, as many as 5 types (JS, JF, FJS, FJF and W), of which over 67% were dynamic JS serves (jumping serve). The serve element has been modified over the years to obtain better effects conducive to winning. Ranging from increasing the speed of the serve, eliminating the serves from the spot in favor of the jump serves, to the use of serves to hide the correct hit of the ball (\"Fake\"-FFJ, FJS).

BACKGROUND: Stretching programs are often used to improve muscle stiffness and thereby posterior shoulder tightness (PST); however, knowledge about their effects on the viscoelastic properties of muscles and performance is limited.
OBJECTIVE: The aim of this study was to investigate the effects of a six-week stretching program on the viscoelastic properties of posterior shoulder muscles, shoulder functional performance and range of motion in volleyball players with PST.
METHODS: A Randomized Controlled Trial.
METHODS: Level II.
METHODS: The study was conducted in 34 male (aged 19-26) professional volleyball players with PST. They were randomly assigned to stretching and control groups. A stretching routine (combining sleeper stretch and cross body stretch exercises) was performed in the stretching group for six weeks. Measurements were taken during the first assessment and six weeks after the initiation of stretching for the following: shoulder external/internal rotation range of motion, spike velocity, single arm seated shot-put test, and infraspinatus- posterior deltoid muscle stiffness (by shear wave elastography).
RESULTS: While the stretching group had statistically better results regarding increased shoulder internal rotation (p < 0.01), spike velocity (p = 0.02) and seated single arm shot put distance (p < 0.01), stretching did not have any effect on tissue stiffness.
CONCLUSIONS: A 6-week program of sleeper stretch, and cross body stretch exercises improved shoulder internal rotation and functional performance. A clinically meaningful change in muscle mechanical properties cannot be detected after a 6-week stretching program.

A prevalent overuse injury among athletes, especially to those participating in sports like volleyball that demand repeated overhead motions, is biceps tendinopathy. The painful condition known as biceps brachii tendinopathy is characterized by changes in the structure of the tendon together with chronic degeneration. Furthermore, the biceps aid in the acceleration and deceleration of the arm in numerous overhead sports. The biceps may experience excessive strain as a result of poor training or exhaustion. It is commonly known that the long head of the biceps tendon plays a significant role in producing pain, particularly when it comes to anterior shoulder discomfort and dysfunction in athletes and working people. Athletes\' biceps tendon conditions fall into three broad categories: degeneration, instability, and abnormalities that are of source. This case details the use of kettlebell eccentric exercise and kinesio taping in the rehabilitation of a young volleyball player with biceps tendinopathy. The four primary aspects of the rehabilitation regimen were kinesio taping, pain management and rest, eccentric training with kettlebells, and initial assessment and patient education. Kettlebell eccentric training was used to enhance eccentric strength and encourage tendon remodeling, and kinesio taping was used to give pain relief and structural stability. This case study emphasizes the value of an all-encompassing rehabilitation strategy catered to the unique requirements of every athlete by demonstrating the effectiveness of kinesio taping and eccentric exercise with kettlebells in the treatment of biceps tendinopathy.

This study aimed to elucidate the impact of combining Beta-Alanine (BA) supplementation with short sprint interval training on cardiorespiratory fitness, anaerobic power, and bio-motor abilities in volleyball players. Twenty young male athletes were randomly divided into 2 equal groups and performed 8 weeks of short sprint interval training while supplementing 4.8 g daily BA or placebo (polydextrose). The players were evaluated for volleyball-specific bio-motor abilities (vertical jump, horizontal jump, spike jump, block jump, 10-m linear sprint, and T-test change of direction speed) and physiological parameters (cardiorespiratory fitness and anaerobic power) pre- and post-intervention. Both groups demonstrated significant (p ≤ 0.05) improvements in all measured variables over time. A time-regimen interaction was observed in jumping ability enhancement from pre- to post-training, wherein BA elicited more significant changes in both vertical and horizontal jumps compared to the placebo. Analyzing residuals in changes and the coefficient of variations (CV) in mean group changes demonstrated that BA supplementation results in uniformly inducing adaptive changes among individuals. Therefore, in light of these results, it is recommended that coaches and trainers take into consideration the utilization of BA as an ergogenic aid to enhance the vertical and horizontal jumps of volleyball players and increase the homogeneity in adaptive responses over the training period.

Coordinative patterns require experience and learning to be acquired, producing movements that offer efficient solutions to various situations and involving certain degree of variability. This coordination variability implies functionality in movement, but it can be impacted by the type of sport practice from early years. The purpose of this work is to analyze the coordination variability and coordination patterns in a specific action such as single-leg landing in children practicing gymnastics, volleyball and non-sporting children. Thirty children (15 girls) performed 10 successful trials of single-leg landing from a height of 25 cm. A motion capture system (9 cameras) was used to capture 3D thigh and shank kinematics. To identify the significant effect of children\'s groups on coordination and coordination variability during single-leg landing, one-dimensional Statistical Parametric Mapping (SPM) was used. Regarding the coordination patterns, in the frontal plane, during the attenuation phase of single-leg landing, the control group exhibited a higher frequency of Anti-Phase with proximal dominancy compared to the sport groups (i.e., gymnastics, and volleyball). In addition, in the sagittal plane during the second peak phase, volleyball players exhibited a higher coordination variability than the gymnastics. The children in the control group showed a greater frequency of antiphasic movements, which indicates the influence of training at an early age, being a determining factor in the increase or not of variability.

This study aimed to investigate the effect of a 12-wk extracurricular volleyball training on working memory from both behavioral and cerebral aspects. A total of 80 children were randomized assigned to (i) the experimental group, who engaged in extracurricular volleyball training for 60 min, thrice a week for 12 wk, and (ii) the control group, who maintained their regular daily routine. Working memory was evaluated in both groups using the N-back task before and after the intervention. Furthermore, functional near-infrared spectroscopy was employed to monitor the level of oxygenated hemoglobin in the prefrontal cortex. The experimental group performed better in the behavioral task than the control group, as evidenced by a shorter response time and a higher correct rate. The functional near-infrared spectroscopy results suggested that the activation of the left dorsolateral prefrontal cortex was significantly higher in the experimental group than in the control group. In addition, correlation analyses showed that the enhancement of left dorsolateral prefrontal cortex activation was significantly correlated with decreasing response time and improving response accuracy in the N-back task. These findings suggest that the left dorsolateral prefrontal cortex is likely the neural substrate for improved working memory performance elicited by 12-wk open skill exercise.