The aim of this study was to examine the differences in muscle architecture during isometric tests between children and adults. Eight boys (age= 11.2 ± 0.26 years) and eight men (age= 22.3 ± 2.01 years) performed plantar flexion isometric efforts at angles of -15°, 0°, 15° at 0%, 40%, 60%, 80% of MVC. Analysis of variance tests indicated that adults showed greater fascicle length from rest to 80% of MVC (p < .05), greater pennation angle at 80% and 100% of MVC (p < .05) and greater aponeuroses displacement at levels of effort greater than 60% of MVC (p < .05). These differences observed in MG would appear to favor better utilization of the force-length and the force-velocity relationships, of the muscle in adults compared with children.
Theodoros Kannas, Eleftherios Kellis, Fotini Arampatzi and Eduardo Saez Saez de Villarreal
Abbas Asadi, Hamid Arazi, Warren B. Young and Eduardo Sáez de Villarreal
To show a clear picture about the possible variables of enhancements of change-of-direction (COD) ability using longitudinal plyometric-training (PT) studies and determine specific factors that influence the training effects.
A computerized search was performed, and 24 articles with a total of 46 effect sizes (ESs) in an experimental group and 25 ESs in a control group were reviewed to analyze the role of various factors on the impact of PT on COD performance.
The results showed that participants with good fitness levels obtained greater improvements in COD performance (P < .05), and basketball players gained more benefits of PT than other athletes. Also, men obtained COD results similar to those of women after PT. In relation to the variables of PT design, it appears that 7 wk (with 2 sessions/wk) using moderate intensity and 100 jumps per training session with a 72-h rest interval tends to improve COD ability. Performing PT with a combination of different types of plyometric exercises such as drop jumps + vertical jumps + standing long jumps is better than 1 form of exercise.
It is apparent that PT can be effective at improving COD ability. The loading parameters are essential for exercise professionals, coaches, and strength and conditioning professionals with regard to the most appropriate dose-response trends to optimize plyometric-induced COD-ability gains.
Javier Raya-González, Luis Suárez-Arrones, Archit Navandar, Carlos Balsalobre-Fernández and Eduardo Sáez de Villarreal
Context: As the number of injuries in young soccer players increases, an epidemiological study is the first step in improving preventive strategies. Objectives: To analyze the injury profile of a Spanish professional soccer club’s academy during 4 consecutive seasons and to examine the injury incidence across different chronological age groups. Design: Prospective cohort design. Setting: Aggregate injury and exposure data collected during 4 consecutive seasons. Participants: Three hundred nine elite male young soccer players. Main Outcomes Measures: Injuries that led to participation time missed from training and match play prospectively reported by medical or coaching staff of the club. Results: A total of 464 time-loss injuries were observed during this study period. The overall injury incidence was 2.93 injuries per 1000 hours, with higher incidence during matches than during training (10.16 vs 2.10 injuries/1000 h; rate ratio [RR] = 0.21; 95% confidence interval [CI], 0.17–0.25; P < .05), with the U14 age group presenting the lowest injury rate (2.39 injuries/1000 h; RR = 1.15–1.57; P < .05). In terms of injury severity, moderate injuries were the most frequent (1.42 injuries/1000 h). Muscle injuries were the most common type of injuries (57.7%; 2.75 injuries/1000 h; RR = 1.84–13.4; P < .05), and hamstrings (93/268) were the most affected muscle group (0.58 injuries/1000 h; RR = 1.58–2.91; P < .05). Injury incidence showed a seasonal variation as indicated by peaks in August and October. In matches, specifically, the match period between 75 and 90 minutes showed the highest injury incidence (10.29 injuries/1000 h; RR = 1.89–6.38; P < .01). Conclusions: The findings of this study suggest that specific preventive strategies must be implemented to try to reduce the injury incidence in Spanish elite young soccer players attending to the characteristics of each age group.
Jaime Fernandez-Fernandez, Eduardo Sáez De Villarreal, David Sanz-Rivas and Manuel Moya
The aim of this study was to analyze the effects of an 8-week (conducted biweekly for a total of 16 sessions) plyometric training program (PT) (e.g., upper- and lower-body exercises) combined with regular tennis training on physical qualities in young tennis players.
Sixty tennis players between the ages of 12 and 13 years (age 12.5 ± 0.3 years, weight 44.2 ± 7.0 kg, height 156.6 ± 7.1 cm) were allocated to either the control group (standard in-season regimen) (CG; n = 30) or the experimental group, which received an additional PT (TG; n = 30) for 30–60 min as a substitute for some tennis training within the usual 90-min practice.
Pre- and posttests included: anthropometric measures; vertical countermovement jump (CMJ); standing long jump (SLJ); 20 m sprint time (with 5 and 10 m splits); a modified 505 agility test; overhead medicine ball throw; and serve velocity test.
After the training intervention, the TG showed significant (p < .01) improvements in all the parameters analyzed, with percentages of change and effect sizes ranging from 3.1% to 10.1% and 0.4 (small) to 1.3 (moderate), respectively. No significant changes were observed in the CG after the training intervention.
PT was shown as an important stimulus for enhancing explosive actions in young tennis players.
Nacho Torreño, Diego Munguía-Izquierdo, Aaron Coutts, Eduardo Sáez de Villarreal, Jose Asian-Clemente and Luis Suarez-Arrones
To analyze the match running profile, distance traveled over successive 15 min of match play, heart rates (HRs), and index of performance efficiency (effindex) of professional soccer players with a global positioning system (GPS) and HR in official competition.
Twenty-six professional players were investigated during full matches in competitive club-level matches (N = 223). Time–motion data and HR were collected using GPS and HR technology.
The relative total distance was 113 ± 11 m/min, with substantial differences between halves. For all playing positions, a substantial decrease in total distance and distance covered at >13.0 km/h was observed in the second half in comparison with the first. The decrease during the second half in distance covered at >13.0 km/h was substantially higher than in total distance. The average HR recorded was 86.0% maximal HR, and the relationship between external and internal load (effindex) was 1.3, with substantial differences between halves in all playing positions, except strikers for effindex. Wide midfielders reflected substantially the lowest mean HR and highest effindex, whereas center backs showed substantially the lowest effindex of all playing positions.
The current study confirmed the decrement in a player’s performance toward the end of a match in all playing positions. Wide midfielders displayed the highest and fittest levels of physical and physiological demands, respectively, whereas center backs had the lowest and least-fit levels of physical and physiological demands, respectively. The position-specific relationship between external and internal load confirms that players with more overall running performance during the full match were the best in effindex.