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1.  Reducing muscle injuries and reinjuries in one italian professional male soccer team 
Summary
Background.
The incidence rate of muscle injuries and re-injuries in professional elite soccer players actually is very high and may interfere with the fate of a championship.
Purpose.
To investigate the effect of a two-tiered injury prevention programme on first injury and re-injury incidence in top level male soccer players.
Study design
Case Series Study.
Muscle injuries and re-injuries sustained by a group of 36 soccer player of an italian elite soccer team have been collected during 2010–2011 season. These data have been compared with those collected during the previous season in the same elite soccer team.
Results.
A total of 64 injuries occurred, 36 (56%) of which during practice and 28 (44%) during matches. Muscle injuries accounted for 31.3% of the total (n=20), 70% (n=14) of which occurred during practice and 30% (n=6) during matches.
Hamstring were the muscles most often injured (n=11) In all, 3 re-injuries occurred (15% of muscle injuries). No early re-injuries occurred. The incidence was 2.5 injuries/1000 hours and the burden was 37 days absence/1000 hours.
Conclusions.
Through the implementation of a group and personalized injury prevention program, we were able to reduce the total number of muscle injuries and days absent because of injury, in a team of elite soccer players, as compared to the previous season. Specifically, muscle injuries accounted for 31% of all injuries, as compared to 59% of all injuries sustained by the team during the previous season. The number of injuries/1000 hours of exposure was reduced by half (from 5.6 to 2.5) and the days absent/1000 hours fell from 106 to 37.
PMCID: PMC3940507  PMID: 24596697
muscle injuries; football; prevention
2.  Development of Body Composition, Hormone Profile, Physical Fitness, General Perceptual Motor Skills, Soccer Skills and On-The-Ball Performance in Soccer-Specific Laboratory Test Among Adolescent Soccer Players 
The aim of the present study was to examine the development of on-the-ball skills in soccer-specific laboratory test and to examine how traditional measures of body composition, hormone profile, physical fitness, general perceptual motor skills and soccer skills were related to performance measured in open skill environment among 10, 12, and 14-year-old regional male soccer players (n = 12/group). The measured variables were height, weight, fat, muscle mass, testosterone, 10m sprint, agility, counter movement jump, peripheral awareness, Eye- Hand-Foot coordination, passing skill, dribbling skill and on-the-ball skills (performance time and passing accuracy) in soccer-specific laboratory test. A significant main effect by age was found in all measured variables except in fat, in peripheral awareness and in passing accuracy. In discriminant analysis 63.9% (λ = 0.603, F = 4.600, p < 0.01) of the players were classified correctly based on physical fitness and general perceptual motor skills into three ability groups originally classified with performance time in soccer-specific laboratory test. Correlation co- efficient analysis with-in age groups revealed that variables associated with performance time in soccer-specific laboratory test were peripheral awareness (r = 0.72, p < 0.01) in 10-year-olds; testosterone (r = -0.70, p < 0.05), dribbling skill (r = 0.73, p < 0.01) and passing skill (r = 0.73, p < 0.01) in 12-year-olds; agility (r = 0.79, p < 0.01), counter movement jump (r = - 0.62, p < 0.01), dribbling skill (r = 0.80, p < 0.01) and passing skill (r = 0.58, p < 0. 05) in 14-year olds. Corresponding relationships with passing accuracy were weight (r = 0.59, p < 0.05), fat (r = 0.66, p < 0.05), 10m sprint (r = 0.71, p < 0.01) and countermovement jump (r = -0.64, p < 0.05) in 10-year-olds; Eye-Hand-Foot coordination (r = 0.63, p < 0.05) in 14-year- olds. The relationship between soccer-specific anticipation time and performance time in soccer- specific laboratory test was significant only in the 14-year-old age group (r = 0.76, p < 0.01). To conclude, on-the-ball skill performance in soccer-specific laboratory test improved with age and it seemed that soccer-specific perceptual skills became more and general perceptual motor skills less important with age in soccer-specific laboratory test.
Key pointsPhysical fitness characteristics and general perceptual motor skills predicted performance time of the open skill soccer-specific laboratory test in the group of 10-14 year-old regional soccer players.Before puberty the players were able to compensate weaker soccer-specific skills with better general physical performance abilities.Soccer-specific skills became more important with age and at the age of 14 the players were not able to compensate soccer-specific skills with general physical performance abilities.Beside basic ball-handling skills it also important to recognize the importance of soccer-specific perceptual skills (anticipation and reaction) as a part of successful soccer performance.
PMCID: PMC3761817  PMID: 24149780
Football,; youth,; perception,; growth,; puberty.
3.  The cardiovascular profile of soccer referees: an echocardiographic study 
Background
During a soccer game, the cardiovascular system is severely taxed The referees must be alert and their level of fitness must be such that fatigue will not impair their decision-making. Referee's peak overall performance is usually after 40 when the performance starts to decline. We evaluated the morphological and functional cardiac profile of professional soccer referees.
Materials and methods
We submitted to a clinical and echocardiographic exam a group of 120 professional soccer referees aged 25 – 45 years, including the first division of the Italian Championship, matched with 120 soccer players, including élite soccer players. Data were compared using an unpaired Student's t test. Statistical significance was with p < 0.05.
Results
Right ventricle dimensions (22.2 ± 3.8 vs 25.9 ± 2.4 mm) and Left Ventricular Mass Index (LVMi) (100.5 ± 45.2 vs 105.4 ± 17.3) were significantly greater in referees than in active soccer players. Left atrium dimensions (33.7 ± 8.9 vs 36.2 ± 3.1 mm), aortic root (29.7 ± 7.9 vs 32.1 ± 3 mm) and LVMi (115.1 ± 16.7 vs 134.1 ± 19.9 g/m2) were significantly greater in élite soccer players than in first-division referees.
Conclusion
Our investigation shows that right ventricle is greater in referees than in soccer players. The differences (left atrium, aortic root and LVMi) between first division referees and élite soccer players may derive from the different training workloads.
doi:10.1186/1476-7120-6-8
PMCID: PMC2259300  PMID: 18269755
4.  Effectiveness of an injury prevention programme for adult male amateur soccer players: a cluster-randomised controlled trial 
British Journal of Sports Medicine  2012;46(16):1114-1118.
Background
The incidence rate of soccer injuries is among the highest in sports, particularly for adult male soccer players.
Purpose
To investigate the effect of the ‘The11’ injury prevention programme on injury incidence and injury severity in adult male amateur soccer players.
Study design
Cluster-randomised controlled trial.
Methods
Teams from two high-level amateur soccer competitions were randomly assigned to an intervention (n=11 teams, 223 players) or control group (n=12 teams, 233 players). The intervention group was instructed to perform The11 in each practice session during one soccer season. The11 focuses on core stability, eccentric training of thigh muscles, proprioceptive training, dynamic stabilisation and plyometrics with straight leg alignment. All participants of the control group continued their practice sessions as usual.
Results
In total, 427 injuries were recorded, affecting 274 of 456 players (60.1%). Compliance with the intervention programme was good (team compliance=73%, player compliance=71%). Contrary to the hypothesis, injury incidences were almost equal between the two study groups: 9.6 per 1000 sports hours (8.4–11.0) for the intervention group and 9.7 (8.5–11.1) for the control group. No significant differences were found in injury severity, but a significant difference was observed in the location of the injuries: players in the intervention group sustained significantly less knee injuries.
Conclusions
This study did not find significant differences in the overall injury incidence or injury severity between the intervention and control group of adult male soccer players. More research is recommended, focusing on injury aetiology and risk factors in adult male amateur soccer players.
doi:10.1136/bjsports-2012-091277
PMCID: PMC3596860  PMID: 22878257
5.  The Relationship Between Imagery Type and Collective Efficacy in Elite and Non Elite Athletes 
This study investigated the relationship between imagery function and individual perceptions of collective efficacy as a function of skill level. Elite (n = 70) and non elite (n = 71) athletes from a number of interactive team sports completed the Sport Imagery Questionnaire (SIQ) and the Collective Efficacy Inventory (CEI). Multiple hierarchical regression analysis was then used to examine which SIQ sub-scales predicted individual perceptions of collective efficacy. For the elite sample, Motivational General-Mastery (MG-M) imagery accounted for approximately 17% of the variance in collective efficacy scores. No significant predictions were observed in the non elite sample. The findings suggest MG-M imagery as a potential technique to improve levels of collective efficacy although competitive level may moderate the effectiveness of such interventions.
Key pointsAs imagery is an individual intervention, an examination of individual perceptions of collective efficacy was most appropriate.Elite athletes who use more MG-M imagery also have higher individual perceptions of collective efficacy.For non-elite athletes, none of the imagery functions tested predicted individual perceptions of collective efficacy.Performance accomplishments provided by MG-M imagery may increase individual perceptions of collective efficacy.Future research should investigate further the effects of imagery intervention programmes on collective efficacy beliefs.
PMCID: PMC3786238  PMID: 24149327
Mental rehearsal; mental skills; team confidence; self efficacy; group dynamics
6.  Energy Expenditure and Intensity of Physical Activity in Soccer Referees During Match-Play 
The aim of this study was to determine the caloric expenditure and the intensity of physical activities performed by official soccer referees during a match expressed in Metabolic Equivalent (METs). The physical activity of referees accredited by CBF (Brazilian Confederation of Soccer) was video-recorded during twenty-nine official games of Paraná Championship (Brasil), Series A and B of the 2005/2006. Computerized video analysis was used to determine the time spent in 6 locomotor activities (standing still, walking, jogging, backwards running, running and sprint). The frequency and duration of each activity were recorded and these data were utilized to calculate the distance covered by the referee. Energy expenditure values were estimated, utilizing specific equations, from the time players spent in each motor activity. The referees observed in this study had a mean age of 38.9 ± 3.8 years, body mass of 86.1 ± 7.1 kg, stature of 1.80 ± 0.07 m and a body mass index of 26.5 ± 0.6 kg·m-2. During match-play, referees covered an average distance of 9155.4 ± 70.3 meters (8411 - 9765), with a mean energy expenditure of 734.7 ± 65 kcal. This energy expenditure was significantly reduced in the second half: 359.9 ± 6.3 vs 374.7 ± 6.6 kcal (p = 0.006), and averaged to be moderate energy intensity (5 METs) with predominant utilization of the aerobic energy system. In total, during 67% of match-play the intensity was equal or lower than 3.8 METs and in 33% it was higher than 9.8 METs. The pattern of movement observed in the present study confirms that soccer refereeing may be considered as a highly intermittent exercise mode. The high to low-intensity activity ratio may be defined as 1:7.1. In conclusion, referees officiating in professional soccer matches in Brazil should perform a physical conditioning regime that provides the stamina required at this level and consume appropriate and adequate nutrition to meet the energetic demands for match-play.
Key pointsIn order to elaborate a diet that sufficiently restores the athlete’s energy expenditure during training and/or competition, the first step would be to measure energy expenditure during activity.We observed that during officials matches soccer referees perform physical aerobic activities of low and moderate intensity, and present a significant decline in energy expenditure between the first and second half.The pattern of movement observed in the present report confirms that soccer referees, like players undertake intermittent type exercise.Nutritional habits of soccer referees must be adapted to their daily physical activities, short training periods and moderate energy intensity physical activity, on average, during match refereeing.
PMCID: PMC3761902  PMID: 24149899
Motion-analysis; referee; football; METs; oxygen consumption
7.  DHA- Rich Fish Oil Improves Complex Reaction Time in Female Elite Soccer Players 
Omega-3 fatty acids (n-3) has shown to improve neuromotor function. This study examined the effects of docosahexaenoic acid (DHA) on complex reaction time, precision and efficiency, in female elite soccer players. 24 players from two Spanish female soccer Super League teams were randomly selected and assigned to two experimental groups, then administered, in a double-blind manner, 3.5 g·day-1 of either DHA-rich fish oil (FO =12) or olive oil (OO = 12) over 4 weeks of training. Two measurements (pre- and post-treatment) of complex reaction time and precision were taken. Participants had to press different buttons and pedals with left and right hands and feet, or stop responding, according to visual and auditory stimuli. Multivariate analysis of variance displayed an interaction between supplement administration (pre/post) and experimental group (FO/OO) on complex reaction time (FO pre = 0.713 ± 0.142 ms, FO post = 0.623 ± 0.109 ms, OO pre = 0.682 ± 1.132 ms, OO post = 0.715 ± 0.159 ms; p = 0.004) and efficiency (FO pre = 40.88 ± 17.41, FO post = 57.12 ± 11.05, OO pre = 49.52 ± 14.63, OO post = 49. 50 ± 11.01; p = 0.003). It was concluded that after 4 weeks of supplementation with FO, there was a significant improvement in the neuromotor function of female elite soccer players.
Key pointsThe results obtained from the study suggest that supplementation with DHA produced perceptual-motor benefits in female elite athletes.DHA could be a beneficial supplement in sports where decision making and reaction time efficiency are of importance.
PMCID: PMC3761870  PMID: 24149875
Fatty acids; omega 3; efficiency; decision-making
8.  Positive Imagery Cognitive Bias Modification in Treatment-Seeking Patients with Major Depression in Iran: A Pilot Study 
Cognitive bias modification paradigms training positive mental imagery and interpretation (imagery CBM-I) hold promise for treatment innovation in depression. However, depression is a global health problem and interventions need to translate across settings and cultures. The current pilot study investigated the impact of 1 week of daily imagery CBM-I in treatment-seeking individuals with major depression in outpatient psychiatry clinics in Iran. Further, it tested the importance of instructions to imagine the positive training materials. Finally, we examined the effects of this training on imagery vividness. Thirty-nine participants were randomly allocated to imagery CBM-I, a non-imagery control program, or a no treatment control group. Imagery CBM-I led to greater improvements in depressive symptoms, interpretive bias, and imagery vividness than either control condition at post-treatment (n = 13 per group), and improvements were maintained at 2-week follow-up (n = 8 per group). This pilot study provides first preliminary evidence that imagery CBM-I could provide positive clinical outcomes in an Iranian psychiatric setting, and further that the imagery component of the training may play a crucial role.
doi:10.1007/s10608-014-9598-8
PMCID: PMC3951961  PMID: 24634554
Mental imagery; Cognitive bias modification; Depression; Computerized interventions; Interpretive bias
9.  Executive Functioning in Highly Talented Soccer Players 
PLoS ONE  2014;9(3):e91254.
Executive functions might be important for successful performance in sports, particularly in team sports requiring quick anticipation and adaptation to continuously changing situations in the field. The executive functions motor inhibition, attention and visuospatial working memory were examined in highly talented soccer players. Eighty-four highly talented youth soccer players (mean age 11.9), and forty-two age-matched amateur soccer players (mean age 11.8) in the age range 8 to 16 years performed a Stop Signal task (motor inhibition), the Attention Network Test (alerting, orienting, and executive attention) and a visuospatial working memory task. The highly talented soccer players followed the talent development program of the youth academy of a professional soccer club and played at the highest national soccer competition for their age. The amateur soccer players played at a regular soccer club in the same geographical region as the highly talented soccer players and play in a regular regional soccer competition. Group differences were tested using analyses of variance. The highly talented group showed superior motor inhibition as measured by stop signal reaction time (SSRT) on the Stop Signal task and a larger alerting effect on the Attention Network Test, indicating an enhanced ability to attain and maintain an alert state. No group differences were found for orienting and executive attention and visuospatial working memory. A logistic regression model with group (highly talented or amateur) as dependent variable and executive function measures that significantly distinguished between groups as predictors showed that these measures differentiated highly talented soccer players from amateur soccer players with 89% accuracy. Highly talented youth soccer players outperform youth amateur players on suppressing ongoing motor responses and on the ability to attain and maintain an alert state; both may be essential for success in soccer.
doi:10.1371/journal.pone.0091254
PMCID: PMC3954684  PMID: 24632735
10.  Short-Term High Intensity Plyometric Training Program Improves Strength, Power and Agility in Male Soccer Players 
Journal of Human Kinetics  2013;36:17-26.
The aim of the present study was to investigate the effects of a short-term in-season plyometric training program on power, agility and knee extensor strength. Male soccer players from a third league team were assigned into an experimental and a control group. The experimental group, beside its regular soccer training sessions, performed a periodized plyometric training program for six weeks. The program included two training sessions per week, and maximal intensity unilateral and bilateral plyometric exercises (total of 40 – 100 foot contacts/session) were executed. Controls participated only in the same soccer training routine, and did not perform plyometrics. Depth vertical jump height, agility (Illinois Agility Test, T Agility Test) and maximal voluntary isometric torque in knee extensors using Multicont II dynamometer were evaluated before and after the experiment. In the experimental group small but significant improvements were found in both agility tests, while depth jump height and isometric torque increments were greater. The control group did not improve in any of the measures. Results of the study indicate that plyometric training consisting of high impact unilateral and bilateral exercises induced remarkable improvements in lower extremity power and maximal knee extensor strength, and smaller improvements in soccer-specific agility. Therefore, it is concluded that short-term plyometric training should be incorporated in the in-season preparation of lower level players to improve specific performance in soccer.
doi:10.2478/hukin-2013-0002
PMCID: PMC3661889  PMID: 23717351
knee extensors; depth jump; dynamometer; unilateral; plyometrics
11.  The Relative Age Effect in Youth Soccer Players from Spain 
The purpose of this study was to identify the existence of Relative Age Effect (RAE) at youth level in both elite and amateur Spanish soccer clubs, and also to carry out an analysis providing with information on how this effect has evolved in recent years. We have obtained information on the youth teams of the 20 clubs belonging to the Spanish Professional Football League (LFP) in two separate seasons (2005-2006 and 2008-2009) as well as data on five youth academies belonging to amateur clubs. The collected data revealed an over- representation of players born in the first months of the selection year in all groups of analysis (Elite 2005-2006, Elite 2008-2009 and Amateurs), although only the Elite groups showed significant variations in birth-date distribution in relation to the Spanish population. The results showed a reduction in RAE from the 2005-2006 season to the 2008-2009 season. The following variables - playing position, the number of years each player has spent in their specific age group and the category of the team at each club were shown not to have influence on the extent of RAE.
Key pointsThere was RAE in all groups analyzed, although only the Elite groups showed significant variations in birth-date distribution in relation to the general population.RAE is more evident in the Elite groups than in the Amateur probably because of the detection process, which is more thorough in the Elite groups.Playing position, number of years in their specific age group and category of the team did not have any influence on the extent of RAE.Any attempts to prevent RAE should be based on a stable sport policy and the implication of all the stakeholders in the system. All of them should think in the development of a player as a long-term project.
PMCID: PMC3761747  PMID: 24149685
Relative age effect; season-of-birth bias; selection processes; talent identification; youth soccer
12.  Sex Differences in Head Acceleration During Heading While Wearing Soccer Headgear 
Journal of Athletic Training  2008;43(6):578-584.
Context:
Researchers have indicated that female soccer players may be at greater risk of concussion compared with their male counterparts. Soccer headgear is marketed for reducing head acceleration and risk of concussion.
Objective:
To determine the effect of sex and soccer headgear on head impact kinematics and dynamic stabilization during soccer heading.
Design:
Cross-sectional design.
Setting:
Research laboratory.
Patients or Other Participants:
Forty-four college-aged soccer players (29 women, 15 men).
Intervention(s):
Using a head impact model, participants performed 4 soccer headers under 3 headgear conditions (control, Head Blast Soccer Band, and Full90 Select Performance Headguard).
Main Outcome Measure(s):
Dependent variables assessed before soccer heading were head-neck anthropometrics and isometric neck muscle strength, and those assessed during soccer headers were resultant linear head acceleration, Head Injury Criteria (HIC36), and superficial neck muscle electromyography. Statistical analyses included multivariate and univariate analyses of variance with repeated measures, independent-samples t tests, appropriate follow-up analyses of variance and post hoc t tests, and Pearson product moment correlations (α  =  .05).
Results:
Head acceleration in women was 32% and 44% greater than in men when wearing the Head Blast (21.5 g versus 16.3 g) and Full90 Select (21.8 g versus 15.2 g), respectively (P < .05). Compared with men, women exhibited 10% greater head accelerations (20.2 g versus 18.2 g) during the control condition (P  =  .164).
Conclusions:
Female soccer players exhibited greater head accelerations than their male counterparts when wearing headgear. Our results are important clinically because they indicate that soccer headgear may not be an appropriate head injury prevention tool for all athletes.
PMCID: PMC2582549  PMID: 19030135
head impact kinematics; concussion pathomechanics; brain injuries; football players
13.  Psychophysiological responses in the pre-competition period in elite soccer players 
This study investigated pre-competition physiological and psychological states of eighteen elite soccer players. Salivary cortisol was assessed during a non- training day and before three league games. Affective states (unpleasant and pleasant, somatic and transactional emotions) were evaluated using the Tension and Effort-Stress Inventory before the three league games. Participants formed 2 groups, 11 starters and 7 non-starters, depending on the starting list established by the coach. All players reported more intense pleasant transactional and somatic emotions than unpleasant ones prior to all games (p < 0.05), and relatively stable profiles of these psychological responses were observed across the three league games. However, salivary cortisol levels increased during pre-game for all players in comparison with the non- training day (p < 0.001). This anticipatory rise was only related to unpleasant somatic emotions (p < 0.001). This demonstrates that cortisol can be used as an index of emotional response to competition.
Key pointsElite athletes perceive the participation to competition as a challenging situation as they experience more pleasant emotions than unpleasant ones in the pre-competition period. This profile is relatively stable across three league games, which is possibly due to the athletes' experience at this level.Participation to competition lead to anticipatory acute response of cortisol in the pre-competition period, which potentially prepares the athlete to perform.These responses are not related to status player (e.g., starter versus non-starter)Physiological stress (e.g. anticipatory rise in cortisol concentrations) is related to negative somatic emotions.Cortisol may constitute a measure of emotional response in pre-competition period.
PMCID: PMC3761908  PMID: 24149949
Emotions; affect; salivary cortisol
14.  Effects of public posting, goal setting, and oral feedback on the skills of female soccer players. 
We evaluated the effects of public posting, goal setting, and oral feedback on the skills of 3 female high school soccer players during practice scrimmages. The dependent variables were the percentage of appropriate responses when the player (a) kept and maintained possession of the ball, (b) moved to an open position during a game restart (e.g., goal or corner kick), and (c) moved to an open position after passing the ball. We also assessed the extent to which changes in practice performances generalized to games. A social validity questionnaire was completed by both players and coaches to assess the acceptability of the intervention's goals, procedures, and outcomes. Results indicate that the intervention was effective in improving performances during practice scrimmages but produced limited generalization to game settings.
doi:10.1901/jaba.2002.35-247
PMCID: PMC1284383  PMID: 12365738
15.  The Effect of Fatigue on Kicking Velocity in Soccer Players 
Journal of Human Kinetics  2012;35:97-107.
Soccer is a game in which fatigue can negatively influence players’ performance. Few studies have examined the practical effects of fatigue on soccer performance skills. Thus, the aim of the present study was to evaluate the effect of fatigue, acutely induced by means of a soccer specific circuit on ball velocity. Ten amateur soccer players (age 27.3 ± 5.25 yr; experience 16,8 ± 6.05 yr; level secondary division; body height 1,80 m ± 0,06; body mass 75,7 kg ± 5,78), participated in this study and performed maximal instep kicks before and after the implementation of an intensive, intermittent and repeated exercise protocol. Analysis of variance with repeated measures indicated a significant decrease (p<0.05) in ball velocity after just one round of the fatigue circuit. However, after the third circuit ball velocity increased and after the fifth circuit maximal ball velocity increased yet again (compared to the second circuit) and was not significantly different from before commencement of the fatigue protocol. The results partly confirmed the hypothesis of the negative influence of fatigue upon ball velocity in soccer kicking, demonstrating also some variability in the presented values of ball velocity perhaps theoretically accounted for by the general governor model.
doi:10.2478/v10078-012-0083-8
PMCID: PMC3588689  PMID: 23486374
kicking velocity; soccer; fatigue; general governor model
16.  Does an in-Season 6-Week Combined Sprint and Jump Training Program Improve Strength-Speed Abilities and Kicking Performance in Young Soccer Players? 
Journal of Human Kinetics  2013;39:157-166.
The aim of this study was to examine the effect of a six-week combined jump and sprint training program on strength-speed abilities in a large sample of youth competitive soccer players. It was hypothesized that the experimental training group would enhance their jumping and sprinting abilities. Enhancement of kicking performance was also hypothesized due to an expected increase in explosive strength established by a plyometric and sprinting regimen. Fifty-two young male soccer players playing at the national level (aged 13.4 ± 1.4 years, body mass 53.4 ± 11.7 kg, body height 1.66 ± 0.11 m) took part in the study. Half of the group underwent the plyometric and sprint training program in addition to their normal soccer training, while the other half was involved in soccer training only. The plyometric training group enhanced their running (+1.7 and +3.2%) and jumping performance (+7.7%) significantly over the short period of time, while the control group did not. Furthermore, both groups increased their kicking velocity after just six weeks of training (+3.3 vs. 6.6%). The findings suggest that a short in-season 6-week sprint and jump training regimen can significantly improve explosive strength in soccer-specific skills and that these improvements can be transferred to soccer kicking performance in terms of ball speed.
doi:10.2478/hukin-2013-0078
PMCID: PMC3916921  PMID: 24511351
speed training; lower extremity; kicking; soccer
17.  EFFECTS OF TWO TYPES OF TRUNK EXERCISES ON BALANCE AND ATHLETIC PERFORMANCE IN YOUTH SOCCER PLAYERS 
Purpose/Background:
Many athletes perform trunk stabilization exercises (SE) and conventional trunk exercises (CE) to enhance trunk stability and strength. However, evidence regarding the specific training effects of SE and CE is lacking and there have been no studies for youth athletes. Therefore, the purpose of this study was to investigate the training effects of SE and CE on balance and athletic performance in youth soccer players.
Methods:
Twenty‐seven male youth soccer players were assigned randomly to either an SE group (n = 13) or CE group (n = 14). Data from nineteen players who completed all training sessions were used for statistical analyses (SE, n = 10; CE, n = 9). Before and after the 12‐week intervention program, pre‐ and post‐testing comprised of a static balance test, Star Excursion Balance Test (SEBT), Cooper’s test, sprint, the Step 50, vertical jump, and rebound jump were performed. After pre‐testing, players performed the SE or CE program three times per week for 12 weeks. A two‐way repeated‐measures ANOVA was used to assess the changes over time, and differences between the groups. Within‐group changes from pre‐testing to post‐testing were determined using paired t‐tests. Statistical significance was inferred from p < 0.05.
Results:
There were significant group‐by‐time interactions for posterolateral (p = 0.022) and posteromedial (p < 0.001) directions of the SEBT. Paired t‐tests revealed significant improvements of the posterolateral and posteromedial directions in the SE group. Although other measurements did not find group‐by‐time interactions, within‐group changes were detected indicating significant improvements in the static balance test, Cooper’s test, and rebound jump in the only SE group (p < 0.05). Vertical jump and sprint were improved significantly in both groups (p < 0.05), but the Step 50 was not improved in either group (p > 0.05).
Conclusions:
Results suggested that the SE has specific training effects that enhance static and dynamic balance, Cooper’s test, and rebound jump.
Level of Evidence:
3b
PMCID: PMC3924608  PMID: 24567855
core training; stabilization exercise; trunk muscle; trunk stability
18.  The Effects of Injury Preventive Warm-Up Programs on Knee Strength Ratio in Young Male Professional Soccer Players 
PLoS ONE  2012;7(12):e50979.
Purpose
We aimed to investigate the effect of FIFA 11+ (11+) and HarmoKnee injury preventive warm-up programs on conventional strength ratio (CSR), dynamic control ratio (DCR) and fast/slow speed ratio (FSR) in young male professional soccer players. These ratios are related to the risk of injury to the knee in soccer players.
Methods
Thirty-six players were divided into 3 groups; FIFA 11+, HarmoKnee and control (n = 12 per group). These exercises were performed 3 times per week for 2 months (24 sessions). The CSR, DCR and FSR were measured before and after the intervention.
Results
After training, the CSR and DCR of knee muscles in both groups were found to be lower than the published normal values (0.61, 0.72, and 0.78 during 60°.s−1, 180°.s−1 and 300°.s−1, respectively). The CSR (60°.s−1) increased by 8% and FSR in the quadriceps of the non-dominant leg by 8% in the 11+. Meanwhile, the DCR in the dominant and non-dominant legs were reduced by 40% and 30% respectively in the 11+. The CSR (60°.s−1) in the non-dominant leg showed significant differences between the 11+, HarmoKnee and control groups (p = 0.02). As for the DCR analysis between groups, there were significant differences in the non-dominant leg between both programs with the control group (p = 0.04). For FSR no significant changes were found between groups.
Conclusions
It can be concluded that the 11+ improved CSR and FSR, but the HarmoKnee program did not demonstrate improvement. We suggest adding more training elements to the HarmoKnee program that aimed to enhance hamstring strength (CSR, DCR and FSR). Professional soccer players have higher predisposition of getting knee injuries because hamstring to quadriceps ratio were found to be lower than the average values. It seems that the 11+ have potentials to improve CSR and FSR as well as prevent knee injuries in soccer players.
doi:10.1371/journal.pone.0050979
PMCID: PMC3513304  PMID: 23226553
19.  The Impact of Moderate and High Intensity Total Body Fatigue on Passing Accuracy in Expert and Novice Basketball Players 
Despite the acknowledged importance of fatigue on performance in sport, ecologically sound studies investigating fatigue and its effects on sport-specific skills are surprisingly rare. The aim of this study was to investigate the effect of moderate and high intensity total body fatigue on passing accuracy in expert and novice basketball players. Ten novice basketball players (age: 23.30 ± 1.05 yrs) and ten expert basketball players (age: 22.50 ± 0.41 yrs) volunteered to participate in the study. Both groups performed the modified AAHPERD Basketball Passing Test under three different testing conditions: rest, moderate intensity and high intensity total body fatigue. Fatigue intensity was established using a percentage of the maximal number of squat thrusts performed by the participant in one minute. ANOVA with repeated measures revealed a significant (F 2,36 = 5.252, p = 0.01) level of fatigue by level of skill interaction. On examination of the mean scores it is clear that following high intensity total body fatigue there is a significant detriment in the passing performance of both novice and expert basketball players when compared to their resting scores. Fundamentally however, the detrimental impact of fatigue on passing performance is not as steep in the expert players compared to the novice players. The results suggest that expert or skilled players are better able to cope with both moderate and high intensity fatigue conditions and maintain a higher level of performance when compared to novice players. The findings of this research therefore, suggest the need for trainers and conditioning coaches in basketball to include moderate, but particularly high intensity exercise into their skills sessions. This specific training may enable players at all levels of the game to better cope with the demands of the game on court and maintain a higher standard of play.
Key PointsAim: to investigate the effect of moderate and high intensity total body fatigue on basketball-passing accuracy in expert and novice basketball players.Fatigue intensity was set as a percentage of the maximal number of squat thrusts performed by the participant in one minute.ANOVA with repeated measures revealed a significant level of fatigue by level of skill interaction.Despite a significant detriment in passing-performance in both novice and expert players following high intensity total body fatigue, this detriment was not as steep in the expert players when compared to the novice players
PMCID: PMC3827563  PMID: 24259994
Squat thrusts; ecological validity; anaerobic
20.  Resistance Training and Head-Neck Segment Dynamic Stabilization in Male and Female Collegiate Soccer Players 
Journal of Athletic Training  2005;40(4):310-319.
Context: Cervical resistance training has been purported to aid in reducing the severity of brain injuries in athletes.
Objective: To determine the effect of an 8-week resistance-training program on head-neck segment dynamic stabilization in male and female collegiate soccer players.
Design: Pretest and posttest control group design.
Setting: University research laboratory and fitness center.
Patients or Other Participants: Thirty-six National Collegiate Athletic Association Division I collegiate soccer players (17 men, 19 women).
Intervention(s): The resistance training group underwent an 8-week cervical resistance training program that consisted of 3 sets of 10 repetitions of neck flexion and extension at 55% to 70% of their 10-repetition maximum 2 times a week. Participants in the control group performed no cervical resistance exercises.
Main Outcome Measure(s): Head-neck segment kinematics and stiffness, electromyographic activity of the upper trapezius and sternocleidomastoid muscles during force application to the head, and neck flexor and extensor isometric strength.
Results: No kinematic, electromyographic, or stiffness training effects were seen. The posttest resistance training group isometric neck flexor strength was 15% greater than the pretest measurement. Isometric neck extensor strength in the female resistance training group was 22.5% greater at the posttest than at the pretest. Women's neck girth increased 3.4% over time regardless of training group level. Women exhibited 7% less head-neck segment length and 26% less head-neck segment mass than men.
Conclusions: Despite increases in isometric strength and girth, the 8-week isotonic cervical resistance training did not enhance head-neck segment dynamic stabilization during force application in collegiate soccer players. Future researchers should examine the effect of head-neck segment training protocols that include traditional and neuromuscular activities (eg, plyometrics) with the focus of reducing head acceleration on force application.
PMCID: PMC1323293  PMID: 16404453
cervical musculature; concussion; head acceleration
21.  Offensive Sequences in Youth Soccer: Effects of Experience and Small-Sided Games 
Journal of Human Kinetics  2013;36:97-106.
The present study aimed to analyze the interaction and main effects of deliberate practice experience and small-sided game format (3 vs. 3 and 6 vs. 6 plus goalkeepers) on the offensive performance of young soccer players. Twenty-eight U-15 male players were divided into 2 groups according to their deliberate practice experience in soccer (i.e., years of experience in federation soccer): Non-Experienced (age: 12.84 ± 0.63 years) and Experienced (age: 12.91 ± 0.59 years; experience: 3.93 ± 1.00 years). The experimental protocol consisted of 3 independent sessions separated by one-week intervals. In each session both groups performed each small-sided game during 10 minutes interspersed with 5 minutes of passive recovery. To characterize the recorded offensive sequences we used the Offensive Sequences Characterization System, which includes performance indicators previous applied in other studies. No interaction effects on the offensive performance were found between both factors. Non-parametric MANOVA revealed that the factor “experience level” had a significant effect (p<0.05) on performance indicators that characterize the development of offensive sequences, especially in 6 vs. 6 + GKs. While experienced players produced longer offensive sequences with greater ball circulation between them, the non-experienced participants performed faster offensive sequences with a predominance of individual actions. Furthermore, significant differences were observed (p<0.05) in the development and finalization of offensive sequences within each group, when comparing small-sided game formats. Evidence supports that small-sided games can serve several purposes as specific means of training. However, the manipulation of game format should always consider the players’ individual constraints.
doi:10.2478/hukin-2013-0010
PMCID: PMC3661899  PMID: 23717359
association football; constraints-led approach; performance; skill acquisition
22.  Effects of the 11+ and Harmoknee Warm-up Programs on Physical Performance Measures in Professional Soccer Players 
The purpose of this study was to examine the effects of the 11+ and HarmoKnee warm-up programs on performance measures in professional soccer players. Thirty-six male professional soccer players (age: 18.9 ± 1.4 years) were divided into 3 groups, the 11+, HarmoKnee and control group (n = 12 per group). The experimental groups performed the programs 3 times per week for 2 months (24 sessions), whereas the control group only performed their regular soccer training. The performance tests carried out were: 10m speed tests with and without a ball, 20m single sprint, vertical jump, Wall-Volley and Illinois agility tests. The 11+ group demonstrated significant increases from pre-to-post time points in the vertical jump (3.7%), Wall- Volley (5.4%) and Illinois agility tests (1.7%), while the HarmoKnee group showed a significant increase in Wall-Volley test, with a 5.2% increase. The repeated measures analysis revealed differences between the groups (large effect size) in the 11+ and HarmoKnee groups, compared to the control group, in 10m speed tests with and without a ball, 20m single sprint and Illinois agility tests (p < 0.05). Thus 8-weeks performing the 11+ warm-up program can enhance jump height, agility and soccer skill while the HarmoKnee program generally only improves soccer skill in young professional male soccer players.
Key PointsThe 11+ improves performance by means of Illinois agility, vertical jump and Wall-Volley tests whereas HarmoKnee improves Wall-Volley test. Incorporating 11+ as a part of the warm-up program by the young teams would be beneficial in agility, leg power and soccer skill respectively.Further modification of both programs may be required to fully realize the players' speed performance potential.Data from this research can be helpful for soccer trainers in choosing programs to enhance performances in young male professional soccer players.
PMCID: PMC3772593  PMID: 24149156
Performance; vertical jump; Illinois agility test; sprint; Wall-Volley test
23.  A Multilevel Approach to the Path to Expertise in Three Different Competitive Settings 
The objectives of the study were to analyze the deliberate practice variables in three different youth competitive sport settings; to analyze the effects of a season-long exposure on deliberate practice variables. The study explores three contexts in two different sports, soccer and volleyball, and at two competitive levels. The athletes fulfilled the questionnaire at the beginning and at the end of the season. A multilevel analysis was performed. Forty eight boys aged 15-17 years (14 from a volleyball club; 14 from an elite volleyball centre; 20 from a professional soccer club) participated in the study. The measure was an adapted version for soccer and volleyball of the Deliberate Practice Motivation Questionnaire, which assesses two dimensions: the will to compete and the will to excel. Fewer people in the volleyball group showed a will to excel, the soccer group showed an increase in the scores. In will to compete, the three teams showed a decrease in their means. The decrease is more pronounced in the will to excel but the context effect is not significant. The biggest decrease is shown by the elite volleyball team, followed by the club teams. The findings raise questions for managers and coaches who look for physical and technical gifted young athletes and aim to develop their qualities through a careful planned training programme. The insertion in programmes that are believed to foster expertise seems to have unexpected consequences. Sport participation cannot rely exclusively on an orientation toward expertise, forgetting the autonomy of young people to set their goals.
Key PointsThe need for the adolescents to focus on game performance can be a deterrent for their own perspectives of a career or just to have fun.The crucial factor to influence the players’ answers seems to be the perspective of a rewarding professional career in sport.It is possible that young athletes, after a hard season, re-evaluate their priorities and think that their dedication to sport did not fit their initial expectations.Managers and coaches should be aware of important pedagogical implications, and the effectiveness of sport participation cannot rely exclusively on an orientation toward expertise.
PMCID: PMC3918554  PMID: 24570621
Deliberate practice; multilevel; expertise; soccer; volleyball
24.  Effects of a Caffeine-Containing Energy Drink on Simulated Soccer Performance 
PLoS ONE  2012;7(2):e31380.
Background
To investigate the effects of a caffeine-containing energy drink on soccer performance during a simulated game. A second purpose was to assess the post-exercise urine caffeine concentration derived from the energy drink intake.
Methodology/Principal Findings
Nineteen semiprofessional soccer players ingested 630±52 mL of a commercially available energy drink (sugar-free Red Bull®) to provide 3 mg of caffeine per kg of body mass, or a decaffeinated control drink (0 mg/kg). After sixty minutes they performed a 15-s maximal jump test, a repeated sprint test (7×30 m; 30 s of active recovery) and played a simulated soccer game. Individual running distance and speed during the game were measured using global positioning satellite (GPS) devices. In comparison to the control drink, the ingestion of the energy drink increased mean jump height in the jump test (34.7±4.7 v 35.8±5.5 cm; P<0.05), mean running speed during the sprint test (25.6±2.1 v 26.3±1.8 km · h−1; P<0.05) and total distance covered at a speed higher than 13 km · h−1 during the game (1205±289 v 1436±326 m; P<0.05). In addition, the energy drink increased the number of sprints during the whole game (30±10 v 24±8; P<0.05). Post-exercise urine caffeine concentration was higher after the energy drink than after the control drink (4.1±1.0 v 0.1±0.1 µg · mL−1; P<0.05).
Conclusions/significance
A caffeine-containing energy drink in a dose equivalent to 3 mg/kg increased the ability to repeatedly sprint and the distance covered at high intensity during a simulated soccer game. In addition, the caffeinated energy drink increased jump height which may represent a meaningful improvement for headers or when players are competing for a ball.
doi:10.1371/journal.pone.0031380
PMCID: PMC3279366  PMID: 22348079
25.  Serum concentrations of two biochemical markers of brain tissue damage S‐100B and neurone specific enolase are increased in elite female soccer players after a competitive game 
Background
It is a matter of debate whether or not ordinary heading of the ball in soccer causes injury to brain tissue.
Objective
To analyse concentrations of the biochemical markers of brain tissue damage S‐100B and neurone specific enolase (NSE) in serum of female elite soccer players in association with a competitive game.
Methods
Venous blood samples were obtained from 44 female soccer players before and after a competitive game for analysis. The number of headers and trauma events (falls, collisions, etc) was assessed from videotape recordings for each player.
Results
Concentrations of both brain damage markers were increased after the game (S‐100B, 0.18 (0.11) v 0.11 (0.05) μg/l (p  =  0.000); NSE, 10.14 (1.74) v 9.05 (1.59) μg/l (p  =  0.001)). There was a significant correlation between changes in S‐100B concentrations and both the number of headers (r  =  0.430, p  =  0.004) and the number of other trauma events (r  =  0.517, p<0.001).
Conclusion
The concentrations of both S‐100B and NSE were increased by game associated activities and events. The increases in S‐100B concentration were significantly related to the number of headers and other trauma events, which indicates that both these factors may have contributed to these increases.
doi:10.1136/bjsm.2005.021584
PMCID: PMC2577522  PMID: 16556784
brain injury; biochemical markers; concussion; soccer

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