Latest research in football - week 25 - 2016

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Level of functional capacities following soccer-specific warm up methods among elite collegiate soccer players
Reference: J Sports Med Phys Fitness. 2016 Jul 6. [Epub ahead of print]
Authors: Vazini Taher A, Parnow A
Summary: Different methods of warm up may have implications in improving various aspects of soccer performance. The present study aimed to investigate acute effects of soccer specific warm up protocols on functional performance tests. This study using randomized within-subject design, investigated the performance of 22 collegiate elite soccer player following soccer specific warm ups using dynamic stretching, static stretching, and FIFA 11+ program. Post warm up examinations consisted: 1) Illinois agility test, 2) Vertical jump, 3) 30 meter sprint, 4), Consecutive turns 5) flexibility of Knee. Vertical jump performance was significantly lower following static stretching, as compared to dynamic stretching (p=0.005). Sprint performance declined significantly following static stretching as compared to FIFA 11+ (p=0.023). Agility time was significantly faster following dynamic stretching as compared to FIFA 11+ (p=0.001) and static stretching (p=0.001). Knee flexibility scores were significantly improved following the static stretching as compared to dynamic stretching (p=016). No significant difference was observed for consecutive turns between three warm up protocol. The present finding showed that a soccer specific warm-up protocol relied on dynamic stretching is preferable in enhancing performance as compared to protocols relying on static stretches and FIFA 11+ program. Investigators suggest that while different soccer specific warm up protocols have varied types of effects on performance, acute effects of dynamic stretching on performance in elite soccer players are assured, however application of static stretching in reducing muscle stiffness is demonstrated.

#2 Practitioners' Perceptions of the Soccer Extra-Time Period: Implications for Future Research
Reference: PLoS One. 2016 Jul 6;11(7):e0157687. doi: 10.1371/journal.pone.0157687.
Authors: Harper LD, Fothergill M, West DJ, Stevenson E, Russell M
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Summary: Qualitative research investigating soccer practitioners' perceptions can allow researchers to create practical research investigations. The extra-time period of soccer is understudied compared to other areas of soccer research. Using an open-ended online survey containing eleven main and nine sub questions, we gathered the perceptions of extra-time from 46 soccer practitioners, all working for different professional soccer clubs. Questions related to current practices, views on extra-time regulations, and ideas for future research. Using inductive content analysis, the following general dimensions were identified: 'importance of extra-time', 'rule changes', 'efficacy of extra-time hydro-nutritional provision', 'nutritional timing', 'future research directions', 'preparatory modulations' and 'recovery'. The majority of practitioners (63%) either agreed or strongly agreed that extra-time is an important period for determining success in knockout football match-play. When asked if a fourth substitution should be permitted in extra-time, 67% agreed. The use of hydro-nutritional strategies prior to extra-time was predominately considered important or very important. However; only 41% of practitioners felt that it was the most important time point for the use of nutritional products. A similar number of practitioners account (50%) and do not (50%) account for the potential of extra-time when training and preparing players and 89% of practitioners stated that extra-time influences recovery practices following matches. In the five minute break prior to extra-time, the following practices (in order of priority) were advocated to players: hydration, energy provision, massage, and tactical preparations. Additionally, 87% of practitioners advocate a particular nutritional supplementation strategy prior to extra-time. In order of importance, practitioners see the following as future research areas: nutritional interventions, fatigue responses, acute injury risk, recovery modalities, training paradigms, injury epidemiology, and environmental considerations. This study presents novel insight into the practitioner perceptions of extra-time and provides information to readers about current applied practices and potential future research opportunities.

#3 Relationships Between Measures Of Physical Fitness Change When Age Dependent Bias Is Removed In A Group Of Young Male Soccer Players
Reference: J Strength Cond Res. 2016 Jun 30. [Epub ahead of print]
Authors: James RS, Thake CD, Birch S
Summary: Age dependent bias is a key issue within talent identification of children, particularly when measures of physical fitness are used. Coaches in sport would benefit from a relatively straightforward method to remove age dependent bias, enabling identification of children who are relatively high performers for their age. This study aimed to determine whether removal of age effects caused changes in the relationships between physical performance and anthropometric measures commonly used in talent identification and development systems. Sixty male soccer players, aged 11 to 17 years, underwent measures of anthropometry, muscular power, strength, sprint speed, and agility. Most absolute measures of performance were significantly correlated with each other and all performance measures were significantly correlated with age. Age residuals were calculated, for all variables, to determine which players performed relatively well for their age and to investigate age-independent relationships between variables. In general, players with relatively fast sprint performance for their age were taller and had relatively high performance in jump power output and grip strength for their age (r > 0.25 and P < 0.025 in each case). Absolute sprint performance PC1 was significantly correlated with absolute agility performance PC1 (r = 0.473, P < 0.001). However, there was no significant relationship between age independent measures of agility and any other measures. Usage of age residuals highlights performers that have relatively high physical fitness for their age. Such analyses may assist the talent identification and development processes as long as differential rates of physical development between players are also considered.

#4 Platelet-rich plasma in the treatment of acute hamstring injuries in professional football players
Reference: Joints. 2016 Jun 13;4(1):17-23. doi: 10.11138/jts/2016.4.1.017.
Authors: Zanon G, Combi F, Combi A, Perticarini L, Sammarchi L, Benazzo F
Summary: Muscle injuries have a high incidence in professional football and are responsible for the largest number of days lost from competition. Several in vitro studies have confirmed the positive role of platelet-rich plasma (PRP) in accelerating recovery and in promoting muscle regeneration, and not fibrosis, in the healing process. This study examines the results of intralesional administration of PRP in the treatment of primary hamstring injuries sustained by players belonging to a major league football club. Twenty-five hamstring injuries (grade 2 according to MRI classification) sustained by professional football players during a 31-months observation period were treated with PRP and analyzed. Sport participation absence (SPA), in days, was considered to correspond to the healing time, and we also considered the re-injury rate, and tissue healing on MRI. The mean follow-up was 36.6 months (range 22-42). There were no adverse events. The mean SPA for the treated muscle injuries was 36.76±19.02 days. The re-injury rate was 12%. Tissue healing, evaluated on MRI, was characterized by the presence of excellent repair tissue and a small scar. This study confirmed the safety of PRP in treating hamstring lesions in a large series of professional football players. PRP-treated lesions did not heal more quickly than untreated lesions described in the literature, but they showed a smaller scar and excellent repair tissue.

#5 Profile of 1-month training load in male and female football and futsal players
Reference: Springerplus. 2016 May 23;5(1):694. doi: 10.1186/s40064-016-2327-x. eCollection 2016.
Authors: Clemente FM, Nikolaidis PT
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Summary: The aim of this study was to analyse the variance of training load between male and female football and futsal players. The statistical analysis tested the variance between gender and type of sport during training sessions. Fifty-nine male and female amateur football and futsal amateur players were monitored during 48 training sessions. The heart rate (HR) responses and the percentage of time spent in zones of intensity were analysed during training sessions. Differences were found in football between the gender and the dependent variables of %HRmax (p value = 0.001; η (2) = 0.042; minimum effect), %time in Z2 (p value = 0.001; η (2) = 0.054; minimum effect), %time in Z4 (p value = 0.001; η (2) = 0.031; minimum effect) and %time in Z5 (p value = 0.001; η (2) = 0.053; minimum effect). The analysis in male players revealed differences between football and futsal in %HRmax (p value = 0.001; η (2) = 0.172; minimum effect). Similar results were found in female category (p value = 0.001; η (2) = 0.040; minimum effect). In this study it was possible to verify that female players spent more time in high intensity zones and that futsal training sessions are more intense than football sessions. Based on such results, coaches and fitness trainers may identify the physiological characteristics of training load imposed to different sports and genders and optimize the training plan for specific categories.

#6 How Important is the Final Outcome to Interpret Match Analysis Data: The Influence of Scoring a Goal, and Difference Between Close and Balance Games in Elite Soccer: Comment on Lago-Penas and Gomez-Lopez (2014)
Reference: Percept Mot Skills. 2016 Feb;122(1):280-5. doi: 10.1177/0031512515626629. Epub 2016 Feb 1.
Authors: Lupo C, Tessitore A
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Summary: In a recent study, Lago-Penas and Gomez-Lopez (2014) demonstrated that during elite English soccer matches, the percentages of ball possession, entries into the final one-third of the pitch, and shots on goal were lower for the teams with a 1 goal up game status compared to those with 1 goal down condition. In addition, clubs with higher budgets preferred to control the match by dictating the play, primarily through ball possession. Elite soccer coaches may benefit from considering training protocols coherent with the financial budget of their clubs, but these considerations may be valuable also for non-elite soccer clubs. In this comment, studies of various team sports are reviewed, to indicate the need to consider different training drills in relation to competition level, playing positions, and match status of a specific sport discipline.

#7 Effect of High and Low Flexibility Levels on Physical Fitness and Neuromuscular Properties in Professional Soccer Players
Reference: Int J Sports Med. 2016 Jul 13. [Epub ahead of print]
Authors: Rey E, Padrón-Cabo A, Barcala-Furelos R, Mecías-Calvo M
Summary: This study aimed to analyse the impact of high and low flexibility levels of hamstring and quadriceps muscles on physical fitness and neuromuscular properties in professional soccer players. 62 male professional soccer players participated in this study and performed 2 instrumented flexibility tests (passive straight leg raise [PSLR] and quadriceps flexibility [QF]). Anaerobic performance was assessed using countermovement jump (CMJ), Abalakov vertical jump, 20-m sprint, and Balsom agility test. A k-means cluster analysis was performed to identify a cut-off value of hamstring and quadriceps flexibility and classify players as high hamstring flexibility (HHF) and low hamstring flexibility (LHF) or high quadriceps flexibility (HQF) and low quadriceps flexibility (LQF), respectively, according to the PSLR and QF performances. The LQF players performed better than HQF on CMJ (p=0.042, ES: 0.64) and Balsom agility test (p=0.029, ES: 0.68). In addition, LQF showed higher muscular stiffness than HQF players (p=0.002, ES: 0.88). There were no significant differences between HHF and LHF groups. When pooling the HQF and LQF players' data, the Pearson's correlation showed significant moderate positive association between muscular stiffness and QF (r=0.516, p<0.001). These results support the rationale that baseline stiffness is likely to influence athletic performance rather than flexibility level in soccer players.

#8 Head Injuries in Soccer
Reference: Rehabil Nurs. 2016 Jul;41(4):197-201. doi: 10.1002/rnj.249. Epub 2015 Nov 2.
Authors: Myrick KM
Summary: Soccer is currently the most popular and fastest growing sport worldwide, with approximately 265 million registered soccer players existing around the world. The popularity of the sport, coupled with the high incidence of 18.8-21.5 head injuries per 1,000 player hours reported, make it essential that clinicians, coaches, and the athletes, have a solid understanding of head injuries. The successful rehabilitation of athletes with head injuries relies upon early and accurate identification strategies and implementation of appropriate return to play measures across all areas in the continuum of care. Soccer is a frequently played sport, and head injuries are common. Therefore, it is imperative that clinicians, coaches, and the athletes themselves have a solid understanding of head injury prevention, diagnosis, and treatment options. The purpose of this article was to provide rehabilitation nurses with current information regarding frequently occurring head injuries in the widespread sport of soccer.

#9 Predictors of FIFA 11+ Implementation Intention in Female Adolescent Soccer: An Application of the Health Action Process Approach (HAPA) Model
Reference: Int J Environ Res Public Health. 2016 Jul 7;13(7). pii: E657. doi: 10.3390/ijerph13070657.
Authors: McKay CD, Merrett CK, Emery CA
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Summary: The Fédération Internationale de Football (FIFA) 11+ warm-up program is efficacious at preventing lower limb injury in youth soccer; however, there has been poor adoption of the program in the community. The purpose of this study was to determine the utility of the Health Action Process Approach (HAPA) behavior change model in predicting intention to use the FIFA 11+ in a sample of 12 youth soccer teams (coaches n = 10; 12-16 year old female players n = 200). A bespoke cross-sectional questionnaire measured pre-season risk perceptions, outcome expectancies, task self-efficacy, facilitators, barriers, and FIFA 11+ implementation intention. Most coaches (90.0%) and players (80.0%) expected the program to reduce injury risk but reported limited intention to use it. Player data demonstrated an acceptable fit to the hypothesized model (standardized root mean square residual (SRMR) = 0.08; root mean square of error of approximation (RMSEA) = 0.06 (0.047-0.080); comparative fit index (CFI) = 0.93; Tucker Lewis index (TLI) = 0.91) Task self-efficacy (β = 0.53, p ≤ 0.01) and outcome expectancies (β = 0.13 p ≤ 0.05) were positively associated with intention, but risk perceptions were not (β = -0.02). The findings suggest that the HAPA model is appropriate for use in this context, and highlight the need to target task self-efficacy and outcome expectancies in FIFA 11+ implementation strategies.

#10 Mechanisms of Injury as a Diagnostic Predictor of Sport-Related Concussion Severity in Football, Basketball, and Soccer: Results From a Regional Concussion Registry
Reference: Neurosurgery. 2016 Aug;63 Suppl 1:169. doi: 10.1227/01.neu.0000489743.00212.e6.
Authors: Zuckerman SL, Totten D, Rubel K, Kuhn AW, Yengo-Kahn AM, Solomon G, Sills AK
Summary: Through a single-institution sport-related concussion (SRC) registry, we sought to: (1) provide a descriptive analysis of mechanisms of SRC in football, basketball, and soccer and (2) determine if mechanism of injury was associated with symptom duration. A retrospective cohort study was conducted through in-depth patient interviews. Complete data were collected for 295 patients. Mechanisms were stratified into 3 components: a contact mechanism, a player mechanism, and an awareness mechanism. For each sport, each mechanism was compared via 1-way χ analyses. Symptom duration data were represented with Kaplan-Meier survival plots and Cox proportional hazards models to estimate the relationship between the exposure (concussion mechanism) to the time variable outcome (days of symptom duration). The majority of athletes were male (70%) with an average age of 15.9 (±2.0) years. Football was the most represented sport (51%). The most common contact mechanisms were helmet-to-helmet contact in football (74%), ground/equipment in basketball (40%), and player to head in soccer (33%). Helmet-to-helmet contact was significantly overrepresented in football (χ = 69.267, df = 2, P < .001). Within the player mechanism, tackling (33%) and blocking (32%) predominated in football, rebounding (45%) and defense/loose-ball (33%) were most common in basketball, and challenging a player (44%) along with the act of heading (40%) were most commonly reported in soccer. Within the awareness mechanism, basketball (χ = 8.805, df = 1, P = .003) and soccer (χ = 11.255, df = 1, P = .001) players were more likely to be unaware of the oncoming collision. For soccer, being unaware of the oncoming collision was associated with a 2.54 (95% confidence interval, 1.14-5.69) times increased risk of not achieving asymptomatic status. The current study analyzed mechanisms of SRC via a regional sports concussion outcomes registry. In middle school, high school, and collegiate athletes: (1) a helmet-to-helmet collision was most common football mechanism; (2) ground and surrounding equipment and player elbows predominated in basketball; (3) challenging a player and heading were the most common mechanisms of SRC in soccer; and (4) "awareness" of an oncoming collision in soccer was the only mechanism associated with a decreased the risk of prolonged symptom recovery.

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