Purpose: The multidimensional role of hamstring muscle group strength in athletic performance and injury prevention is well documented, and nordic hamstring exercise (NHE) is a popular method for the development of hamstring strength. Our aim was to examine the EMG characteristics of the eccentric NHE as well as the effects of long-term eccentric NHE training on muscle strength and vertical jump performance in 10- to 11-year-old female handball players. Methods: Players from the same handball team were randomly assigned to an eccentric NHE training (13 players) or a control group (10 players). Both groups continued their regular handball training routine, but the NHE group performed additional eccentric NHE exercises once or twice a week, with progressively increasing volume, over 20 weeks. To test training effects, countermovement jump (CMJ) height, eccentric hamstring impulse, peak torque, and angle of peak torque were evaluated before, during and after the training period. In the pre-exercise test, EMG activity of the medial and lateral hamstring muscle was also assessed during NHE. Results: Hamstring activities ranged between 98 and 129%. Lateral hamstring activity was greater than medial only in the right leg during NHE. Eccentric hamstring impulse improved in both legs at 10 weeks in both groups. Then, at 20 weeks, it remained unchanged in the NHE but decreased in controls. A similar adaptation was seen in eccentric hamstring torque, without change in the optimum knee angle. CMJ height improved only in the NHE. Conclusion: It is concluded that NHE activates the hamstring musculature effectively, and a favourable mechanical adaptation to long-term NHE exercise in girls can be triggered as early as 11 years of age.

(1) In the present investigation, we tested the hypothesis that unilateral countermovement jump performance is associated with knee joint stabilization ability during unilateral landing on unstable surface. (2) Twenty-five male sport students were tested for dynamometric knee extension and flexion, and hip abduction isometric strength. Myolectric activity of vastus lateralis and medialis, gluteus medius, and biceps femoris muscles were measured during unilateral countermovement vertical jump performed on a force plate, and during unilateral landing on unstable surface. (3) Vertical jump impulse negatively correlated with biceps femoris activation at landing. Participants with greater hip abduction force performed greater vertical jump impulse, and activated the biceps femoris less when landing on unstable surface. Furthermore, participants with smaller knee flexion/extension torque ratio increased biceps femoris/vastus medialis activation ratio at landing. (4) We conclude that hip abduction strength is an important contributor to unilateral vertical jump performance. Because biceps femoris is considered the synergist of the anterior cruciate ligament, we also propose that hip abductors are primary frontal plane protectors of the knee joint by reducing knee valgus and stress, allowing for smaller biceps femoris co-activation (secondary protection) at landing on unstable surface.

(1) The unilateral countermovement jump is commonly used to examine frontal plane kinetics during unilateral loading and to identify athletes with an increased risk of lower limb injuries. In the present study, we examined the biomechanical mechanisms of knee and pelvis stabilization during unilateral vertical jumps. (2) Healthy males performed jumps on a force plate with the dominant leg. Activity of the dominant-side gluteus medius and the contralateral-side quadratus lumborum and erector spinae muscles was recorded with surface EMG. The EMG data were normalized to the EMG activity recorded during maximal voluntary isometric hip abduction and lateral trunk flexion contractions. During jumps, the propulsive impulse was measured, and the pelvis and thigh segmental orientation angles in the frontal plane were recorded and synchronized with the EMG data. (3) The magnitude of knee valgus during the jump did not correlate with hip abduction force, but negatively correlated with gluteus medius activity. This correlation became stronger when gluteus medius activity was normalized to hip abduction force. Propulsive impulse did not correlate with any neuromechanical measurement. (4) We conclude that hip abduction force itself does not regulate the magnitude of knee valgus during unilateral jumps; rather, the gluteus medius should be highly activated to increase frontal-plane knee joint stability.

Background: Lower-limb asymmetry is linked to injury risk and may impair performance, yet evidence in basketball is inconsistent. A commonly cited 10% threshold is proposed as critical, but its practical relevance in basketball-specific tasks remains unclear. This study examined the effects of asymmetry on vertical jump and agility performance in basketball players, with particular focus on the 10% threshold. Methods: Male university basketball players (n = 20) completed unilateral jump tests (single-leg countermovement jump, single-hop, triple-hop, 6 m hop) and a bilateral COD (change of direction) test to quantify asymmetry. Basketball-specific performance was evaluated using the Lane Agility Test and bilateral countermovement jump. Asymmetry indices were calculated as absolute percentage differences. Paired tests, Welch’s t-tests (<10% vs. ≥10% asymmetry), and Pearson correlations were applied. Results: Significant inter-limb asymmetries were detected across all unilateral tasks (large effect sizes). Players with ≥10% asymmetry showed reduced bilateral countermovement jump height compared to <10% (p = 0.039, d = 1.00). Triple-hop asymmetry correlated strongly with slower Lane Agility Test times (r = 0.62, p = 0.003), while single-leg jump asymmetry correlated moderately and negatively with bilateral countermovement jump height (r = −0.46, p = 0.043). No significant associations were found for COD asymmetry. Conclusions: In the present study, inter-limb asymmetries exceeding 10% were associated with impaired vertical jump performance. Triple-hop asymmetry appears most relevant for agility, whereas COD asymmetry may not adequately reflect basketball-specific demands. Monitoring and reducing inter-limb asymmetries may support both performance and injury prevention.

Objectives: Adolescence is a pivotal stage of development characterized by significant physical, psychological, and social changes. Establishing healthy lifestyle habits during this period is crucial for long-term health and the prevention of chronic diseases. Despite this, global trends show a marked decline in physical activity among adolescents, particularly girls, who are more susceptible to sedentary behaviors. One potential site for intervention to eliminate physical inactivity at the population level is the school educational setting during childhood. Traditional school-based physical exercise programs often adopt a one-size-fits-all approach, which may not address the diverse needs and interests of students, leading to reduced motivation and participation. Personalized physical exercise programs, tailored to individual capabilities and preferences, offer a promising alternative to enhance physical fitness and foster lifelong engagement in physical activity. Methods: A total of 170 Hungarian high school girls (mean age ≈ 15.3 years) were randomly assigned to either a personalized physical exercise group or a control group following the standard curriculum. The intervention spanned two academic years and consisted of five traditional gym classes per week (control group) or three traditional and two individually tailored classes with cardiorespiratory and resistance training per week (intervention group), each lasting 45–60 min. Individual goals were set based on baseline assessments, emphasizing self-referenced progress. Results: The personalized physical exercise group showed significant improvements in body mass index (BMI), body fat percentage, maximum oxygen uptake capacity (VO₂max), muscular strength, and flexibility (p < 0.05), while the control group exhibited minimal or negative changes. Conclusions: The personalized physical exercise program has been shown to be more effective in achieving higher cardiorespiratory performance and favorable body composition among adolescent girls than a traditional school physical education class, highlighting its potential role in school settings.

Background: The anabolic window hypothesis suggests a limited post-exercise period for optimal nutrient uptake and utilization. Prior research indicates that miRNAs in extracellular vesicles (EVs) may regulate post-exercise adaptation by influencing protein synthesis. This study aimed to examine the effects of resistance exercise (RE) on physiological parameters and the expression and function of miRNAs transported in EVs. Methods: Twenty resistance-trained male participants (22 ± 2 years) completed a five-week RE program designed for hypertrophy. They consumed maltodextrin and whey protein based on assigned nutrient timing: immediately post-exercise (AE), three hours post-exercise (AE3), or no intake (CTRL). Body composition and knee extensor strength were assessed. Small EVs were isolated and then validated via three methods. Nanoparticle tracking analysis determined EV concentration and size, followed by pooled miRNA profiling and signaling pathway analysis. Results: Skeletal muscle mass significantly increased in AE (p = 0.001, g = 2) and AE3 (p = 0.028, g = 1), and it was higher in AE compared to CTRL (p = 0.013, η² = 0.41), while knee extensor strength improved only in AE (p = 0.032, g = 0.9). Body fat percentage significantly decreased in all groups, AE (p = 0.005, g = 1.5), AE3 (p = 0.024, g = 1), and CTRL (p = 0.005, g = 1.7). Vesicle concentration significantly increased in the AE group (p = 0.043, r = 0.7), while it decreased in the CTRL group (p = 0.046, r = 0.8). Distinct miRNA expression profiles emerged post-intervention: 20 miRNAs were upregulated in AE, while 13 in AE3 and 15 in CTRL were downregulated. Conclusions: Nutrient timing influences training adaptation but is not more critical than total macronutrient intake. Changes in EV-transported miRNAs may regulate anabolic processes via the PI3K-AKT-mTOR and FoxO pathways through PTEN regulation.