Search Results (258)

Background: Evidence regarding the longitudinal use of infrared thermography in elite under-18 soccer players remains limited. Most previous studies have relied on cross-sectional designs or short observation periods. Methods: This prospective longitudinal observational study monitored 18 elite under-18 male outfield soccer players across 16 official matches (96 valid assessments). Thermographic evaluations were performed 48 h post-match under standardized conditions across six bilateral lower-limb regions. A thermal asymmetry was defined as relevant if ΔTsk ≥ 0.5 °C. Linear mixed-effects models, paired t-tests and chi-square tests were used for statistical analysis. Results: Relevant asymmetries were detected in 79.2% of assessments (mean maximum ΔTsk 0.77 ± 0.43 °C). Posterior Thigh BF (40.6%) and Posterior Thigh ST (35.4%) showed the highest prevalence (χ² = 16.31, p = 0.006). Significant side-to-side differences were found for Anterior Thigh (p = 0.004), Adductor (p = 0.039) and Posterior Thigh BF (p = 0.032). The intraclass correlation coefficient for Thermal Asymmetry Burden was very low (ICC = 0.024). Fifteen athletes (83.3%) showed recurrent asymmetry and 13 (72.2%) showed a recurrent same-region pattern. Match-to-match variation in TAB was significant (Kruskal–Wallis p = 0.025; ANOVA p = 0.011). No time-loss muscle injuries occurred. Conclusions: Post-match thermal asymmetries are highly prevalent in elite youth soccer and appear to reflect dynamic, load-dependent recovery responses rather than stable thermal phenotypes. Longitudinal thermographic monitoring may help characterise individual recovery patterns when interpreted alongside other monitoring tools. Full article

Observing psychological skills in football can inform coaching feedback but is methodologically challenging. Meaningful behaviors can be difficult to isolate from tactical and technical actions due to the game’s complexity. This pilot study asked whether Harwood’s 5Cs framework (commitment, communication, concentration, control, confidence) could be operationalized into a behavioral coding system for central defenders, with what intra-rater consistency a single expert observer could apply it, and what patterns emerged across pre-, mid-, and post-intervention phases. Two youth teams (U15, U17) from a Major League Soccer Development Academy participated. Video footage from 16 competitive matches was analyzed using a template derived from co-designed 5Cs role descriptions. Five central defenders appearing in all three phases were retained for exploratory descriptive analysis. Event-detection agreement was 73.3%; mean intra-operator κ among matched events was 0.917 for behavior type and 0.799 for outcome, falling to 0.427 (95% CI 0.300–0.554) when detection and classification errors were combined. This indicates moderate overall agreement, consistent with single-expert feasibility rather than general reliability. The sample (n = 5) was not powered for inferential comparisons. Patterns are reported descriptively as rates per 90 min, success percentages, and within-player trajectories. The study offers a transparent template for operationalizing the 5Cs as observable behaviors, a prototype rather than a validated instrument. Full article

Background: Anthropometric body-composition assessment in youth soccer commonly relies on equations developed in different source populations and based on distinct body-composition models, potentially altering nutritional and sport-related interpretation. This study compared body-fat estimates from equations intended to report the same outcome, body fat percentage, but based on different operational models, and quantified muscle-mass outputs from anthropometric approaches targeting total-body skeletal, whole-body, and tissue-level muscle compartments in a cohort of Chilean male U-15 and U-16 players. Methods: This secondary cross-sectional method-comparison study analyzed anonymized anthropometric records collected in 2018 from 50 male players. Slaughter, Faulkner, Carter, Deurenberg, and Sloan–Siri estimates of body fat were compared, together with Poortmans, Lee, Doupe, and Kerr muscle-mass approaches. Absolute agreement among adiposity equations was evaluated using a two-way random-effects, absolute-agreement, single-measure ICC [ICC(A,1)] and Bland–Altman analyses. Muscle-mass approaches were compared with repeated-measures analysis; pairwise difference-versus-mean summaries across different muscle constructs were interpreted descriptively rather than as formal agreement tests. Sensitivity analyses excluded Deurenberg and examined a maturation-related Slaughter scenario. Results: Deurenberg yielded the highest body-fat estimate (18.97 ± 3.07%), followed by Slaughter (13.32 ± 3.35%), Faulkner (10.84 ± 1.40%), Sloan-Siri (8.01 ± 2.80%), and Carter (7.91 ± 1.49%). Global differences were large (χ²(4) = 182.96; p < 0.001; Kendall’s W = 0.915), and individual absolute agreement was low [ICC(A,1) = 0.157; bootstrap 95% CI 0.102–0.212]. Excluding Deurenberg did not remove the between-method differences (χ²(3) = 124.44; p < 0.001; W = 0.830). For muscle mass, mean estimates ranged from 25.11 ± 3.07 kg with Poortmans to 31.26 ± 4.94 kg with Doupe, with a significant method effect after Greenhouse–Geisser correction (p < 0.001). Conclusions: The adiposity equations yielded substantially different numerical estimates of the same reported outcome, body fat percentage, and showed low individual-level absolute agreement. Muscle-mass approaches also produced large numerical differences, partly expected because they target different compartments. Outputs from different equations or constructs should not be treated as numerically interchangeable. Because no criterion reference method was included, this study quantifies method dependence rather than validity and cannot identify the most accurate equation. Full article

Background: Physical and technical development in youth soccer depends on the integration of neuromuscular and small-sided games (SSG) training. However, the influence of training sequence on adaptations remains unclear in prepubertal players. Therefore, this study aimed to compare the effects of performing neuromuscular training before or after SSG on physical fitness and soccer-specific performance in trained prepubertal soccer players. Methods: Twenty-two trained prepubertal male soccer players were randomly assigned to either neuromuscular training followed by SSG or SSG followed by neuromuscular training. Both groups completed a 6-week in-season intervention, including two weekly sessions, with each group performing 3 weeks of neuromuscular training and 3 weeks of SSG training in a different order. Physical fitness (back extensor strength, five-jump test, 10 m sprint, and Yo-Yo IR1) and soccer-specific performance (change of direction with ball and Loughborough Soccer Passing Test) were assessed before and after the intervention. Results: All 22 participants completed the intervention (n = 11 per group). Both groups demonstrated significant improvements over time in most physical fitness and soccer-specific performance variables (p < 0.01). However, significant group × time interactions indicated that the magnitude of improvement was consistently greater when neuromuscular training preceded small-sided games (p ≤ 0.041). Compared with the SSG-before-neuromuscular group, the neuromuscular-before-SSG group achieved larger improvements in back strength (+9.8% vs. +2.7%), five-jump test (+17.1% vs. +10.0%), 10 m sprint (−10.3% vs. −6.3%), Yo-Yo IR1 distance (+35.4% vs. +20.4%), change of direction with ball (−7.4% vs. −1.0%), and Loughborough Soccer Passing Test (−16.0% vs. −7.8%). Conclusions: Training sequence may influence the magnitude of short-term adaptations in prepubertal soccer players. Although both training orders improved performance, performing neuromuscular training before SSG resulted in greater improvements in several physical fitness and soccer-specific performance outcomes. These findings suggest that training order may represent an important factor in youth soccer training design; however, further research is required to confirm the consistency of this sequencing effect and to explore the mechanisms underlying these adaptations. Full article

Background: Anthropometric analysis has become a key tool for analyzing body composition to assess, monitor, and track structural changes in soccer players. Objective: The objective of this study was to analyze the scientific literature on body composition and anthropometry in soccer using a bibliometric analysis. Material and Methods: The following databases were consulted: Scopus, Web of Science (WoS), PubMed (Medline), SportDiscus, and the ScienceDirect publishing platform. The study included documents published between 1990 and 2025. Data was selected following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines statement flowchart and subsequently analyzed using Bibliometrix and R software to identify keywords, frequency of occurrence, journal analysis, countries, and other bibliometric indicators. Results: A total of 384 documents met the inclusion criteria. Spain, Italy, Brazil and Portugal stand out as the countries with the highest output. These countries are associated with the most representative authors, led by Suarez-Arrones, L; Nikolaidis, PT; and Campa, F., who are in turn associated with the most representative concepts: “Male”, “Adolescent” and “Athletic performance”. The most prevalent concepts are population-based: “Adolescent” and “Young adult”. The top three organizations in terms of contributing to the scientific study of body composition and anthropometry were the University of the Basque Country, Pablo de Olavide University, and the University of Coimbra. It can be observed that most of the literature has focused on youth (29.16% of the total documents), followed by elite players (22.91%) and professionals (14.84%), where the focus is on those aged 14 to 19 years and playing at highly competitive levels, seeking peak performance. Conclusions: Methodological heterogeneity in evaluation protocols constitutes the main structural shortcoming in this field: 32.29% of studies do not specify their protocols, which compromises the comparability of the results. The widespread adoption of international standards, such as the International Society for the Advancement of Kinanthropometry (ISAK) methodology, along with a requirement to indicate the instrument used and the evaluator’s certification level, is a priority for improving the quality of scientific communication in future research. Full article

Background and Objectives: Efficient landing shock attenuation is important for both athletic performance and lower-extremity injury prevention in youth soccer players. Although landing biomechanics and change-of-direction (COD) performance have been widely investigated, the relationship between field-based COD performance and landing impact characteristics remains unclear. This study aimed to examine the relationships between linear sprint performance, COD performance, and landing impact during a standardized single-leg forward drop jump landing task in junior soccer players. Methods: Thirty-six junior soccer players (22 boys and 14 girls; 10–12 years) participated in this cross-sectional study. Linear sprint performance and COD performance were assessed using a 30 m sprint test and a 30 m zigzag run test, respectively. Landing impact was evaluated during a standardized single-leg forward drop jump landing task using a force plate. Body weight-normalized peak vertical ground reaction force (peak vGRF, %BW) was calculated for each trial, and the average of the final five successful trials was used for analysis. Relationships between performance measures and body weight-normalized peak vGRF were examined using Spearman’s rank correlation coefficients and partial Spearman correlation analyses adjusted for sex. Results: No significant correlation was observed between 30 m sprint performance and body weight-normalized peak vGRF (ρ = 0.106, p = 0.537). In contrast, 30 m zigzag run performance showed a moderate positive correlation with body weight-normalized peak vGRF (ρ = 0.401, p = 0.015), indicating that poorer COD performance was associated with greater landing impact. This association remained significant after adjustment for sex (partial ρ = 0.474, p = 0.004). Conclusions: These findings suggest that landing impact characteristics may represent one biomechanical factor associated with COD performance. Although the observed association was moderate, field-based COD assessments may provide practical information regarding landing impact characteristics. Future studies should incorporate biological maturation, COD deficit, and additional biomechanical variables to further clarify these relationships. Full article

Monitoring physical performance during the pre-season may help coaches and practitioners interpret short-term changes in young soccer players, although group-level analyses may mask individual variability. This observational longitudinal study analyzed short-term changes, individual variability, and associations between baseline performance and change magnitude in 50 under-17 male outfield soccer players during a 47-day pre-season. Physical performance was assessed before and after the pre-season using the squat jump (SJ), countermovement jump (CMJ), 20 m linear sprint (Sprint-20m), 20 m change-of-direction test (COD-20m), and Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IRL1). Significant improvements were observed in SJ (+1.43 cm, p < 0.001), CMJ (+1.37 cm, p < 0.001), and COD-20m (+0.31 km·h⁻¹, p < 0.001), whereas no statistically significant changes were detected in Sprint-20m (−0.14 km·h⁻¹, p = 0.121) or Yo-Yo IRL1 (−26.20 m, p = 0.721). Individual changes were heterogeneous, with 68.0% improving in SJ and COD-20m, 64.0% in CMJ, 40.0% in Sprint-20m, and 54.0% in Yo-Yo IRL1. Exploratory inverse associations were observed between baseline performance and change scores for SJ (ρ = −0.35, p = 0.014), CMJ (ρ = −0.40, p = 0.004), and COD-20m (ρ = −0.30, p = 0.033), whereas no statistically significant associations were detected for Sprint-20m or Yo-Yo IRL1. These findings support integrating group-level changes, individual variability, and baseline-performance context when interpreting short-term physical performance monitoring in youth soccer. Full article

Background: Effective playing time (EPT) is a crucial determinant of the physical, technical, and cognitive development of young soccer players. Reducing match interruptions may enhance game rhythm and support player progression. This study examined the effects of a rapid-restart protocol, based on the availability of spare balls (SB), on EPT, sprint performance, and agility in young Tunisian players. Methods: Sixty male youth players (aged 11–16) from a Tunisian first-division club were randomly assigned to an experimental group (EG, n = 30) or a control group (CG, n = 30) across three age categories (U12, U14, U16). The EG played 10 weekly matches using the rapid-restart protocol, while the CG competed under standard conditions. Sprint performance (5 m, 10 m, 20 m) and agility (Illinois Agility Test, IAT) were assessed at baseline (T0), mid-intervention (T1), and post-intervention (T2). EPT was determined through video analysis. Results: Compared with controls, the EG showed significant improvements in sprint (5 m and 20 m) and IAT performance across all age categories (p < 0.01). EPT increased, providing additional opportunities for ball-in-play exposure during matches. The protocol also reduced contact between ball retrievers and players, thereby improving safety and minimizing interruptions. Conclusions: The rapid-restart protocol (RRP) effectively increased EPT and was associated with improvements in sprint and agility performance. Whether these improvements were mediated by changes in match intensity or physiological load remains to be determined. Its simplicity, low cost, and safety benefits make it a practical strategy for coaches, organizers, and the Tunisian Football Federation. This approach may represent a practical organizational strategy for improving match continuity and EPT during youth soccer competitions. Full article

Background: Pre-season physical monitoring may help coaches understand short-term changes in youth soccer players and examine whether physical indicators are associated with early squad inclusion. This study aimed to analyze changes in physical performance during the pre-season period and to examine whether pre- and post-assessment physical performance differed between squad-included and non-included under-15 male soccer players in the first five official matches of the main competition. Methods: Thirty-seven male outfield players were assessed using the Squat Jump (SJ), Countermovement Jump (CMJ), 20 m linear sprint (Sprint-20 m), 20 m change-in-direction test (COD-20m), and Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IRL1). Squad-included players were those listed in at least one of the first five official match reports, whereas non-included players were not listed in these reports but remained part of the broader under-15 program. Results: Significant increases were observed in SJ (+1.44 cm, p = 0.007), CMJ (+1.36 cm, p = 0.006), and COD-20m (+0.38 km·h⁻¹, p = 0.002), whereas Sprint-20 m and Yo-Yo IRL1 did not change significantly. Fourteen players were squad-included and 23 were non-included. Squad-included players presented higher pre-assessment values for SJ, CMJ, COD-20m, and the exploratory composite physical score, and higher post-assessment values for SJ, CMJ, Sprint-20 m, COD-20m, and the exploratory composite physical score. The largest between-group difference was observed for post-assessment COD-20m (14.19 ± 0.49 vs. 13.40 ± 0.74 km·h⁻¹, p < 0.001, d = 1.25). Conclusions: Early squad inclusion was associated with higher absolute physical performance, particularly post-assessment COD-20m, whereas the magnitude of pre-to-post changes was not clearly associated with squad inclusion. Full article

This study investigated seasonal changes in anthropometric characteristics, vertical and horizontal jump performance, 30 m sprint performance, estimated maximal aerobic capacity, and repeated-sprint ability in competitive youth soccer players across the preparation, mid-season, and end-season phases. A longitudinal repeated-measures design was employed over one competitive season. Anthropometric variables, vertical and horizontal jump performance, 30 m sprint performance, estimated VO₂max derived from the Vam-Eval field test, and repeated-sprint sets (2 × 5 × 20 m with 15 s recovery between sprints and 1 min between sets) were assessed at three time points. Significant seasonal changes were observed in anthropometric characteristics, with body mass and height increasing progressively and body fat percentage decreasing throughout the competitive season (F ≥ 12.0, p < 0.001, η_p² ≥ 0.32). Body mass increased from 64.1 ± 6.7 to 66.7 ± 6.8 kg, height from 1.69 ± 0.07 to 1.72 ± 0.07 m, and body fat percentage decreased from 11.3 ± 2.0% to 9.4 ± 1.8%. Peak height velocity (PHV) significantly influenced changes in body mass and height but not body fat percentage. Seasonal improvements were observed in several physical performance measures. Squat jump, standing long jump, 15 s repeated jump performance, 10- and 30 m sprint performance, estimated maximal aerobic speed, estimated VO₂max, and repeated-sprint performance changed significantly across the season (F ≥ 3.28, p ≤ 0.046, η_p² ≥ 0.11), whereas countermovement jump, five-jump test, and flying 20 m sprint performance remained unchanged. Estimated VO₂max and maximal aerobic speed improved from preparation to mid-season and were subsequently maintained. Repeated-sprint performance exhibited set-dependent seasonal adaptations, with significant Time × Set interactions indicating progressive improvements during the second repeated-sprint set, whereas the first set showed only transient improvements at mid-season. Significant PHV and Time × PHV effects were also observed for aerobic capacity and repeated-sprint performance. In conclusion, these seasonal variations likely reflect the combined influence of biological maturation, training exposure, and competitive demands rather than training effects alone. Full article

High countermovement-jump (CMJ) height prediction may reflect mechanical reconstruction rather than independent neuromuscular information. This study separated mechanically proximal variables from mechanically restricted force-expression, movement-organization, and tensiomyography (TMG) predictors. Sixty-six elite youth football players completed force-platform CMJ and rectus femoris TMG assessments. Jump height was reconstructed from mean propulsion force and propulsion duration. After excluding these variables and direct mechanical equivalents, Ridge, Elastic Net, GAM, and random forest models were evaluated using repeated nested cross-validation, with predictor-set, ablation, and held-out permutation-importance analyses. The mechanical benchmark almost perfectly reconstructed jump height (RMSE = 0.0027 m; predictive R² = 0.998). After mechanical restriction, random forests were the strongest prespecified single model family (RMSE = 0.0510 m; predictive R² = 0.296), whereas the fully nested one-standard-error model-selection pipeline provided a more conservative estimate of generalization (RMSE = 0.0548 m; predictive R² = 0.187). Within the retained predictor set, movement organization provided more information than force expression (predictive R² = 0.214 vs. 0.078). The TMG-only prediction was worse than the mean-level benchmark (predictive R² = −0.039), and adding TMG did not improve the CMJ base model. CMJ height is readily reconstructed from proximal propulsion mechanics. After their removal, movement organization retains modest predictive information, whereas single-muscle rectus femoris TMG did not provide useful standalone or incremental value in this cohort. Full article

Youth soccer performance is influenced by multiple factors, including age, body size, and physical capacities, but the relative contribution of these variables to aerobic and explosive performance remains unclear. Understanding these relationships can improve the interpretation of field tests and support individualized training prescription. This study was designed to examine the association of age category, body mass, and height with physical performance in youth soccer players by jointly considering aerobic and explosive capacities, in order to support the interpretation of field tests within training prescription. Forty-five male players (15 U16, 15 U17, 15 U19) from the same club were assessed across two standardised on-field testing sessions, including the 45–15 test (estimated maximal aerobic speed, MAS) and vertical jump tests (squat jump, SJ; countermovement jump, CMJ; countermovement jump with free arms, CMJ_FH). Performance variables (SJ, CMJ, CMJ_FH, MAS) were treated as outcomes, while category, body mass, and height were included as predictors. A multivariate analysis was performed, followed by univariate analyses for each indicator. Results showed a significant multivariate effect of age category on overall performance (p < 0.001; η²p = 0.482), whereas height and body mass were not significant (p > 0.05). In univariate analyses, age category was associated with all variables: SJ (p = 0.005; adj. R² = 0.160), CMJ (p < 0.001; adj. R² = 0.287), CMJ_FH (p = 0.004; adj. R² = 0.173), and MAS (p < 0.001; adj. R² = 0.352). Performance increased progressively from U16 to U17 to U19, with larger between-category differences in aerobic capacity. In conclusion, age category was more strongly associated with the performance profile than height and body mass when considered jointly; these findings should be interpreted in light of the observational design and the lack of biological maturation measures. Full article

Soccer performance is characterized by high motor and cognitive complexity, resulting from the interaction between, among others, physical and technical components. However, evidence regarding the relationships among physical performance, motor coordination and soccer-specific technical remains limited. Therefore, this cross-sectional study aimed to investigate the associations among these domains in youth soccer players. Forty-nine male U15 participants (age: 14.3 ± 0.5 years) underwent anthropometric assessments, physical fitness testing (10 m, 30 m sprint, CMJ, YYIRT1), a general motor coordination test (Harre Circuit Test), and soccer-specific technical evaluation (F-MARC test battery). Associations among variables were assessed using Spearman correlations and exploratory principal component analysis (PCA) based on a Spearman correlation matrix with oblimin rotation. Significant associations emerged between general motor coordination, physical performance variables, and several soccer-specific technical skills. The PCA identified three partially overlapping components, cumulatively explaining about 70% of the variance, highlighting the multidimensional and interconnected nature of soccer-related performance capacities. General motor coordination demonstrated relevant loadings in both coordinative/technical and physical-performance-oriented domains. These findings suggest that youth soccer performance should not be interpreted through isolated physical or technical characteristics, but rather as the result of interactions among coordinative, neuromuscular, and technical factors. Consequently, multidimensional and individualized training approaches integrating physical, coordinative, and technical stimuli may represent relevant strategies for youth soccer development. Full article

Objective: To examine lower-body stretch–shortening cycle (SSC) indicators across chronological age categories and playing positions in elite male youth soccer players. Methods: In a cross-sectional design, 984 male players from Slovakia (U15–U19) completed Squat Jumps (SJ), Countermovement Jumps (CMJ), and Drop Jumps (DJ) using the OptoJump photocell system. Outcomes included Eccentric Utilization Ratio (EUR), Reactive Strength Index (RSI), DJ Ground Contact Time (DJ GCT), and Jump Heights (JH). Differences were tested using factorial ANCOVA (age category × playing position) adjusted for height and weight, followed by Tukey-adjusted post hoc comparisons (p < 0.05). Results: Significant age-category main effects were observed for DJ RSI, DJ JH, CMJ JH, SJ JH, and DJ GCT. The largest effects were for DJ JH, CMJ JH, and SJ JH (ηp² = 0.096–0.112), whereas the DJ GCT effect was statistically significant but small (ηp² = 0.013). EUR showed no significant differences across age categories (p = 0.586). Positional differences were limited overall and mainly evident in selected U19 outcomes, particularly jump-height variables and DJ GCT. Conclusions: Lower-body SSC performance increased across chronological age categories, with the largest separation in jump-height and reactive strength outcomes. These differences likely reflect a combination of maturation, training exposure, and selection rather than chronological age alone. EUR remained stable across age categories and playing positions, although the JH-based ratio has limited sensitivity in the present test configuration. Positional separation emerged mainly at U19, supporting broad SSC development across earlier youth categories and position-sensitive interpretation in the oldest cohort. Full article

Background: Trunk and pelvic strength balance and functional movement quality are relevant factors for musculoskeletal health and injury-prevention monitoring in youth soccer players. Aim: This study aimed to evaluate longitudinal changes in isometric trunk and pelvic strength balance, functional movement quality, and selected muscle imbalance indicators during a physiotherapy-based strengthening programme in adolescent male soccer players. Methods: A longitudinal single-group repeated-measures study was conducted in male soccer players aged 12–18 years. Isometric strength balance was assessed using the Dr. Wolff Back-Check system, and functional movement quality was evaluated using the Functional Movement Screen (FMS). Complete-case analyses were performed according to available repeated measurements. Results: FMS total scores improved across repeated assessments, whereas the global Back-Check score showed no significant longitudinal change. Component-level and imbalance analyses indicated reductions in adductor–abductor imbalance, and better FMS performance was moderately associated with lower adductor–abductor imbalance. Conclusions: Functional movement quality and selected muscle imbalance indicators demonstrated favorable longitudinal changes during the physiotherapy-based strengthening programme. These findings suggest that physiotherapy-oriented strengthening and movement-control exercises may contribute to improvements in functional movement quality and selected muscle balance indicators in adolescent male soccer players. However, the small repeated-measures subsamples and observational study design limit causal interpretation and generalizability. Full article