Javier Raya-González

Bio: Javier Raya-González is an academic researcher from Pablo de Olavide University. The author has contributed to research in topics: Basketball & Physical fitness. The author has an hindex of 10, co-authored 70 publications receiving 313 citations.

Effects of Plyometric Jump Training on Jump and Sprint Performance in Young Male Soccer Players: A Systematic Review and Meta-analysis.

Abstract: Even from a young age, modern soccer requires high levels of physical fitness development, particularly jumping and sprinting. Plyometric jump training (PJT), combined with young athletes’ regular soccer sessions, has the potential to improve jumping and sprinting. However, studies exploring the effects of PJT are generally limited by small sample sizes. This problem of underpowered studies may, thus, be resolved by pooling study results in a meta-analysis. The objective of this systematic review with meta-analysis (SRMA) was to assess the effects of plyometric jump training (PJT) on jumping and sprinting among young male soccer players. The SRMA included peer-reviewed articles that incorporated PJT in healthy players (i.e., 7 weeks and > 14 PJT sessions induced greater effects compared to PJT with ≤ 7 weeks and ≤ 14 total sessions on 10-m sprint performance (between group p = 0.038). PJT is effective in improving jumping and sprinting performance among young male soccer players. Greater 10-m linear sprinting improvements were noted after interventions > 7-week duration and > 14 sessions, suggesting a greater return from exposure to longer PJT interventions, partially in support for the adoption of a long-term approach to athletic development in young athletes. However, with reference to the findings of the meta-regression, and those from the remaining subgroup and single factors analysis, a robust confirmation regarding the moderator role of participant’s age or PJT configuration effects on young soccer player’s fitness qualities needed.

Determining the Relationship Between Internal Load Markers and Noncontact Injuries in Young Elite Soccer Players.

Abstract: Purpose: To examine the association and predictive ability of internal load markers with regard to noncontact injuries in young elite soccer players. Methods: Twenty-two soccer players (18.6 [0.6] ...

Distribution of External Load During Acquisition Training Sessions and Match Play of a Professional Soccer Team.

Abstract: Castillo, D, Raya-Gonzalez, J, Weston, M, and Yanci, J. Distribution of external load during acquisition training sessions and match play of a professional soccer team. J Strength Cond Res XX(X): 000-000, 2019-The aim of this study was to use global position systems to analyze the external loads of the 3 different acquisition training sessions (ATS) with competitive matches in professional soccer players over a 6-week period. Sixteen professional soccer players participated in the study, which analyzed the distribution of external load during the training microcycle of a professional soccer team. The 3 types of ATS undertaken by the players were as follows: ATS1 (strength), ATS2 (endurance), and ATS3 (speed). The total distance covered, the distance covered at above 14 km·h, the distance covered >21 km·h, the number of high accelerations (>3 m·s), and player load were recorded. The results showed that external loads were consistently higher during matches when compared with all training sessions (range of effect sizes: 1.06-3.38). Between training session comparisons revealed higher external loads during ATS1 and ATS2, when compared with ATS3 (range of effect sizes: 0.60-2.41). The only external load variable that differed between ATS1 and ATS2 was the distance covered >21 km·h, which was higher for ATS1. Our findings suggest that technical staff should consider the physical demands of weekly periodization to understand the training process regarding optimizing player physical performance.

Acute Effects of Caffeine Supplementation on Movement Velocity in Resistance Exercise: A Systematic Review and Meta-analysis.

Abstract: Several studies investigated the effects of caffeine supplementation on movement velocity in resistance exercise. However, these studies presented inconsistent findings. This paper aimed to: (a) review the studies that explored the effects of caffeine supplementation on movement velocity in resistance exercise; and (b) pool their results using a meta-analysis. A search for studies was performed through seven databases. Random-effects meta-analyses of standardized mean differences (SMD) were performed to analyze the data. Sub-group meta-analyses explored the effects of caffeine on different velocity variables (i.e., mean and peak velocity), different loads (i.e., low, moderate, and high loads), and upper- and lower-body exercises. Twelve studies met the inclusion criteria. In the main meta-analysis, in which we pooled all available studies, the SMD favored the caffeine condition (SMD = 0.62; 95% confidence interval [CI]: 0.39–0.84; p < 0.001). Sub-group analyses indicated that caffeine significantly enhances mean (SMD = 0.80; 95% CI: 0.48–1.12; p < 0.001) and peak velocity (SMD = 0.41; 95% CI: 0.08–0.75; p = 0.014), movement velocity with low loads (SMD = 0.78; 95% CI: 0.41–1.14; p < 0.001), moderate loads (SMD = 0.58; 95% CI: 0.25–0.91; p = 0.001), and high loads (SMD = 0.70; 95% CI: 0.33–1.07; p < 0.001), as well as in lower-body (SMD = 0.82; 95% CI: 0.42–1.23; p < 0.001) and upper-body exercises (SMD = 0.59; 95% CI: 0.37–0.82; p < 0.001). Acute caffeine supplementation is highly ergogenic for movement velocity in resistance exercise. Sub-group analyses indicated that caffeine ingestion is ergogenic: (a) for both mean and peak velocity; (b) for movement velocity when exercising with low, moderate and high loads, and (c) for movement velocity in both lower- and upper-body exercises. Previous meta-analyses that explored the effects of caffeine on various aspects of resistance exercise performance (i.e., muscular strength and endurance) reported trivial to moderate ergogenic effects (effect size range: 0.16–0.38). In the present meta-analysis, the pooled effect size ranged from 0.41 to 0.82. From a resistance exercise performance standpoint, this suggests that caffeine has the most pronounced performance-enhancing effects on movement velocity.

The influence of youth soccer players' sprint performance on the different sided games' external load using GPS devices.

Abstract: The aims of this study are 1) to compare sided games’ (SGs) external responses encountered by players according to pitch size and to 2) examine the relationships between sprint performance and SGs’...

Implementing Eccentric Resistance Training-Part 1: A Brief Review of Existing Methods.

Abstract: The purpose of this review was to provide a physiological rationale for the use of eccentric resistance training and to provide an overview of the most commonly prescribed eccentric training methods. Based on the existing literature, there is a strong physiological rationale for the incorporation of eccentric training into a training program for an individual seeking to maximize muscle size, strength, and power. Specific adaptations may include an increase in muscle cross-sectional area, force output, and fiber shortening velocities, all of which have the potential to benefit power production characteristics. Tempo eccentric training, flywheel inertial training, accentuated eccentric loading, and plyometric training are commonly implemented in applied contexts. These methods tend to involve different force absorption characteristics and thus, overload the muscle or musculotendinous unit in different ways during lengthening actions. For this reason, they may produce different magnitudes of improvement in hypertrophy, strength, and power. The constraints to which they are implemented can have a marked effect on the characteristics of force absorption and therefore, could affect the nature of the adaptive response. However, the versatility of the constraints when prescribing these methods mean that they can be effectively implemented to induce these adaptations within a variety of populations.

A re-analysis of the Cochrane Library data: the dangers of unobserved heterogeneity in meta-analyses

Abstract: Background Heterogeneity has a key role in meta-analysis methods and can greatly affect conclusions. However, true levels of heterogeneity are unknown and often researchers assume homogeneity. We aim to: a) investigate the prevalence of unobserved heterogeneity and the validity of the assumption of homogeneity; b) assess the performance of various meta-analysis methods; c) apply the findings to published meta-analyses. Methods and Findings We accessed 57,397 meta-analyses, available in the Cochrane Library in August 2012. Using simulated data we assessed the performance of various meta-analysis methods in different scenarios. The prevalence of a zero heterogeneity estimate in the simulated scenarios was compared with that in the Cochrane data, to estimate the degree of unobserved heterogeneity in the latter. We re-analysed all meta-analyses using all methods and assessed the sensitivity of the statistical conclusions. Levels of unobserved heterogeneity in the Cochrane data appeared to be high, especially for small meta-analyses. A bootstrapped version of the DerSimonian-Laird approach performed best in both detecting heterogeneity and in returning more accurate overall effect estimates. Re-analysing all meta-analyses with this new method we found that in cases where heterogeneity had originally been detected but ignored, 17–20% of the statistical conclusions changed. Rates were much lower where the original analysis did not detect heterogeneity or took it into account, between 1% and 3%. Conclusions When evidence for heterogeneity is lacking, standard practice is to assume homogeneity and apply a simpler fixed-effect meta-analysis. We find that assuming homogeneity often results in a misleading analysis, since heterogeneity is very likely present but undetected. Our new method represents a small improvement but the problem largely remains, especially for very small meta-analyses. One solution is to test the sensitivity of the meta-analysis conclusions to assumed moderate and large degrees of heterogeneity. Equally, whenever heterogeneity is detected, it should not be ignored.

Running-based high-intensity interval training vs. small-sided game training programs: effects on the physical performance, psychophysiological responses and technical skills in young soccer players.

Abstract: This study aimed to compare the effects of 5-week running-based high-intensity interval training (HIIT) vs. small-sided game training (SSG) on the physical performance, psychophysiological responses and technical skills in young soccer players. Twenty young male soccer players (age: 14.2±0.5 years, height: 161.8±7.9 cm) participated in this study and were assigned to two groups: the HIIT group (n=10) and SSG group (n=10). Both groups trained twice per week with a similar total training duration. The SSG consisted of two 5-9 minutes of 2-a-side with 2-minute passive rest periods, whereas the HIIT consisted of 12-20 minutes of continuous runs at intensities (90 to 95%) related to the velocity obtained in the 30-15 intermittent fitness test. Before and after the 5-week training periods the following tests were completed: maximum oxygen consumption (VO2max) from the Yo-Yo Intermittent Recovery Test level 1 (YYIRTL-1), 10-30-m sprint test, countermovement jump [CMJ], squat jump [SJ], and drop jump [DJ]), 1000-m run test, zigzag agility, repeated sprint ability, 30-15 intermittent fitness test and speed dribbling ability test. Our results revealed meaningful improvements in YYIRTL-1 performance (SSG: +12.8%, standardized effect size [d]=-1.46; HIIT: +16.4%, d=3.27 and VO2max (SSG: +3.3%, d=-1.48; HIIT: +4.3%, d=2.61). There was a meaningful greater improvement in agility and technical test performances following the SSG training compared with the HIIT (p ≤ 0.05, d=ranging from 0.92 to 1.99). By contrast, the HIIT group showed meaningfully higher performance responses in terms of the 1000-m running time and repeated sprint test ability (p ≤ 0.05, d=ranging from 0.90 to 2.06). These results confirmed that SSG training might be a more effective training regime to improve technical ability and agility with greater enjoyment, whereas HIIT might be more suitable for speed-based conditioning in young soccer players.

Effects of core strength training using stable versus unstable surfaces on physical fitness in adolescents

Abstract: Background It has been demonstrated that core strength training is an effective means to enhance trunk muscle strength (TMS) and proxies of physical fitness in youth. Of note, cross-sectional studies revealed that the inclusion of unstable elements in core strengthening exercises produced increases in trunk muscle activity and thus provide potential extra training stimuli for performance enhancement. Thus, utilizing unstable surfaces during core strength training may even produce larger performance gains. However, the effects of core strength training using unstable surfaces are unresolved in youth. This randomized controlled study specifically investigated the effects of core strength training performed on stable surfaces (CSTS) compared to unstable surfaces (CSTU) on physical fitness in school-aged children. Methods Twenty-seven (14 girls, 13 boys) healthy subjects (mean age: 14 ± 1 years, age range: 13–15 years) were randomly assigned to a CSTS (n = 13) or a CSTU (n = 14) group. Both training programs lasted 6 weeks (2 sessions/week) and included frontal, dorsal, and lateral core exercises. During CSTU, these exercises were conducted on unstable surfaces (e.g., TOGU© DYNAIR CUSSIONS, THERA-BAND© STABILITY TRAINER). Results Significant main effects of Time (pre vs. post) were observed for the TMS tests (8-22%, f = 0.47-0.76), the jumping sideways test (4-5%, f = 1.07), and the Y balance test (2-3%, f = 0.46-0.49). Trends towards significance were found for the standing long jump test (1-3%, f = 0.39) and the stand-and-reach test (0-2%, f = 0.39). We could not detect any significant main effects of Group. Significant Time x Group interactions were detected for the stand-and-reach test in favour of the CSTU group (2%, f = 0.54). Conclusions Core strength training resulted in significant increases in proxies of physical fitness in adolescents. However, CSTU as compared to CSTS had only limited additional effects (i.e., stand-and-reach test). Consequently, if the goal of training is to enhance physical fitness, then CSTU has limited advantages over CSTS.