Latest research in football - week 52 part II - 2014

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

Following studies were retrieved for this week:


#1 Examining Neurocognitive Function in Previously Concussed Interscholastic Female Soccer Players
Reference: Appl Neuropsychol Child. 2014 Dec 12:1-11. [Epub ahead of print]
Authors: Forbes CR, Glutting JJ, Kaminski TW.
Summary: Awareness of sport-related concussions in soccer has gained recent attention in the medical community. Interestingly, purposeful heading-a unique yet strategic and inherent part of soccer-involves repeated subconcussive blows to the head. We divided 210 female interscholastic soccer players into control (CON [never concussed]) and experimental (EXP [previously concussed]) groups. We assessed neurocognitive performance using the Automated Neuropsychological Assessment Metrics computer program before and after the players' competitive season. Headers were recorded at all sanctioned matches. Data were analyzed using a series of one-way analyses of covariance and t tests. Both groups essentially played in the same number of games (EXP = 16.1 vs. CON = 16.1) and had an equal number of total headers (EXP = 24.9 vs. CON = 24.3). Additionally, headers per game were surprisingly low in both groups (1.4 in EXP vs. 1.3 in CON). Unexpectedly, there were no significant differences between the EXP and CON groups across all dependent variables measured (p > .05). This study suggests that although previously concussed players involve themselves in purposeful heading (i.e., subconcussive insults) throughout a competitive season, there appear to be no negative consequences on neuropsychological test performance or concussion-related symptoms. Additional research is needed to determine what may result during the course of a playing career.

#2 Effect of turf on the cutting movement of female football players
Reference: Journal of Sport and Health Science, Volume 3, Issue 4, December 2014, Pages 314–319 doi:10.1016/j.jshs.2014.07.004
Authors: Strutzenberger G, Cao HM, Koussev J, Potthast W, Irwin G
Gareth Irwina, c
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Summary: The globalisation of artificial turf and the increase in player participation has driven the need to examine injury risk in the sport of football. The purpose of this study was to investigate the surface–player interaction in female football players between natural and artificial turf. Eight university level female football players performed an unanticipated cutting manoeuvre at an angle of 30° and 60°, on a regulation natural grass pitch (NT) and a 3G artificial turf pitch (AT). An automated active maker system (CodaSport CXS System, 200 Hz) quantified 3D joint angles at the ankle and knee during the early deceleration phase of the cutting, defined from foot strike to weight acceptance at 20% of the stance phase. Differences were statistically examined using a two-way (cutting angle, surface) ANOVA, with an α level of p < 0.05 and Cohen's d effect size reported. A trend was observed on the AT, with a reduction in knee valgus and internal rotation, suggesting a reduced risk of knee injury. This findings highlight that AT is no worse than NT and may have the potential to reduce the risk of knee injury. The ankle joint during foot strike showed large effects for an increase dorsiflexion and inversion on AT. A large effect for an increase during weight acceptance was observed for ankle inversion and external rotation on AT. These findings provide some support for the use of AT in female football, with no evidence to suggests that there is an increased risk of injury when performing on an artificial turf. The ankle response was less clear and further research is warranted. This initial study provides a platform for more detailed analysis, and highlights the importance of exploring the biomechanical changes in performance and injury risk with the introduction of AT.

#3 Concussion management in soccer
Reference: Journal of Sport and Health Science, Volume 3, Issue 4, December 2014, Pages 307–313 doi:10.1016/j.jshs.2014.07.005
Authors: Jason P. Mihalik, Robert C. Lynall, Elizabeth F. Teel, Kevin A. Carneiro
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Summary: Brain injuries in sports drew more and more public attentions in recent years. Brain injuries vary by name, type, and severity in the athletic setting. It should be noted, however, that these injuries are not isolated to only the athletic arena, as non-athletic mechanisms (e.g., motor vehicle accidents) are more common causes of traumatic brain injuries (TBI) among teenagers. Notwithstanding, as many as 1.6 to 3.8 million TBI result from sports and recreation each year in the United States alone. These injuries are extremely costly to the global health care system, and make TBI among the most expensive conditions to treat in children. This article serves to define common brain injuries in sport; describe their prevalence, what happens to the brain following injury, how to recognize and manage these injuries, and what you can expect as the athlete recovers. Some return-to-activity considerations for the brain-injured athlete will also be discussed.

#4 Anterior cruciate ligament injuries in soccer: Loading mechanisms, risk factors, and prevention programs
Reference: Journal of Sport and Health Science, Volume 3, Issue 4, December 2014, Pages 299–306 doi:10.1016/j.jshs.2014.06.002
Authors: Boyi Dai, Dewei Mao, William E. Garrett, Bing Yu
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Summary: Anterior cruciate ligament (ACL) injuries are common in soccer. Understanding ACL loading mechanisms and risk factors for ACL injury is critical for designing effective prevention programs. The purpose of this review is to summarize the relevant literature on ACL loading mechanisms, ACL injury risk factors, and current ACL injury prevention programs for soccer players. Literature has shown that tibial anterior translation due to shear force at the proximal end of tibia is the primary ACL loading mechanism. No evidence has been found showing that knee valgus moment is the primary ACL loading mechanism. ACL loading mechanisms are largely ignored in previous studies on risk factors for ACL injury. Identified risk factors have little connections to ACL loading mechanisms. The results of studies on ACL injury prevention programs for soccer players are inconsistent. Current ACL injury prevention programs for soccer players are clinically ineffective due to low compliance. Future studies are urgently needed to identify risk factors for ACL injury in soccer that are connected to ACL loading mechanisms and have cause-and-effect relationships with injury rate, and to develop new prevention programs to improve compliance.

#5 The acute effects of vibration stimulus following FIFA 11+ on agility and reactive strength in collegiate soccer players
Reference: Journal of Sport and Health Science, Volume 3, Issue 4, December 2014, Pages 293–298 doi:10.1016/j.jshs.2014.03.014
Authors: Ross Cloak, Alan Nevill, Julian Smith, Matthew Wyon
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Summary: The aim of this study was to assess the effects of combining the FIFA 11+ and acute vibration training on reactive strength index (RSI) and 505 agility. Seventy-four male collegiate soccer players took part in the study and were randomly assigned to FIFA 11+ with acute vibration group (FIFA + WBV), FIFA 11+ with isometric squat group (FIFA + IS) or a control group consisting of the FIFA 11+ alone (Con). The warm-up consisted of the FIFA 11+ and was administered to all participants. The participants in the acute vibration group were exposed to 30 s whole body vibration in squat position immediately post warm-up. The isometric group completed an isometric squat for 30 s immediately post warm-up. RSI significantly improved pre- to post-intervention amongst FIFA + WBV (p < 0.001) due to a decrease in contact time (p < 0.001) in comparison to FIFA + IS and Con, but 505 agility was not affected. The results of this study suggest the inclusion of an acute bout of WBV post FIFA 11+ warm-up produces a neuromuscular response leading to an improvement in RSI. Future research is required to examine the exact mechanisms behind these improvements amongst other populations and over time course of the performance.

#6 Effects of small-volume soccer and vibration training on body composition, aerobic fitness, and muscular PCr kinetics for inactive women aged 20–45
Reference: Journal of Sport and Health Science Volume 3, Issue 4, December 2014, Pages 284–292 doi:10.1016/j.jshs.2014.07.003
Authors: Luke J. Connolly, Suzanne Scott, Magni Mohr, Giorgos Ermidis, Ross Julian, Jens Bangsbo, Sarah R. Jackman, Joanna L. Bowtell, Rosemary C. Davies, Susan J. Hopkins, Richard Seymour, Karen M. Knapp, Peter Krustrup, Jonathan Fulford
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Summary: The present study investigated the effects of 16 weeks of small-volume, small-sided soccer training soccer group (SG, n = 13) and oscillating whole-body vibration training vibration group (VG, n = 17) on body composition, aerobic fitness, and muscle PCr kinetics in healthy inactive premenopausal women in comparison with an inactive control group (CO, n = 14). Training for SG and VG consisted of twice-weekly 15-min sessions with average heart rates (HRs) of ∼155 and 90 bpm respectively. Pre- and post-measurements of body composition (DXA), phosphocreatine (PCr) on- and off-kinetics, and HR measurements during standardised submaximal exercise were performed. After 16 weeks of training in SG, fat percentage was lowered (p = 0.03) by 1.7% ± 2.4% from 37.5% ± 6.9% to 35.8% ± 6.2% and the PCr decrease in the quadriceps during knee-extension ramp exercise was attenuated (4% ± 8%, p = 0.04), with no changes in VG or CO (time-group effect: p = 0.03 and p = 0.03). Submaximal exercise HR was also reduced in SG after 16 weeks of training (6% ± 5% of HRmax, p = 0.01). Short duration soccer training for 16 weeks appears to be sufficient to induce favourable changes in body composition and indicators of aerobic fitness and muscle oxidative capacity in untrained premenopausal women.

#7 Stress hormonal analysis in elite soccer players during a season
Reference: Journal of Sport and Health Science, Volume 3, Issue 4, December 2014, Pages 279–283 doi:10.1016/j.jshs.2014.03.016
Authors: Yiannis Michailidis
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Summary: The purpose of this study was to evaluate the changes in some hormonal parameters (cortisol, testosterone, ratio of testosterone/cortisol (T/C)) in professional soccer players during a season. Fifteen professional players from a soccer club of the first division of the Greek soccer league participated. All sport medical examinations were conducted four times: before the re-building period, post re-building period, mid-season, and after finishing the competition phase. For testosterone, significant differences were observed between the end season and post re-building period (11.6%; p < 0.05) and mid-season (12.1%; p < 0.05). The cortisol concentration increased at mid-season by approximately 23%, and this change differed significantly from all other measurements for this hormone. The T/C ratio increased at the post re-building period and decreased at the middle of the season. These hormones and their ratios could be used as stress and recovery state indicators. Coaches can use these parameters in combination with other indicators to optimize workloads, and to avoid overreaching and overtraining.

#8 The relative age effect has no influence on match outcome in youth soccer
Reference: Journal of Sport and Health Science Volume 3, Issue 4, December 2014, Pages 273–278 doi:10.1016/j.jshs.2014.07.001
Authors: Donald T. Kirkendall
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Summary: In age-restricted youth sport, the over-selection of athletes born in the first quarter of the year and under-selection of athletes born in the last quarter of the year has been called the relative age effect (RAE). Its existence in youth sports like soccer is well established. Why it occurs has not been identified, however, one thought is that older players, generally taller and heavier, are thought to improve the team's chances of winning. To test this assumption, birth dates and match outcome were correlated to see if teams with the oldest mean age had a systematic advantage against teams with younger mean ages. Player birth dates and team records (n = 5943 players on 371 teams; both genders; U11–U16) were obtained from the North Carolina Youth Soccer Association for the highest level of statewide youth competition. The presence of an RAE was demonstrated with significant oversampling from players born in the 1st vs. the 4th quarter (overall: 29.6% vs. 20.9% respectively, p < 0.0001). Mean team age was regressed on match outcomes (winning %, points/match, points/goal, and goals for, against, and goal difference), but there was no evidence of any systematic influence of mean team age and match outcomes, except possibly in U11 males. Selecting players based on physical maturity (and subsequently, on age) does not appear to have any systematic influence on match outcome or season record in youth soccer suggesting that the selection process should be focused on player ability and not on physical maturation.

#9 Women's football: Player characteristics and demands of the game
Reference: Journal of Sport and Health Science Volume 3, Issue 4, December 2014, Pages 258–272 doi:10.1016/j.jshs.2014.10.001
Authors: Vanessa Martínez-Lagunas, Margot Niessen, Ulrich Hartmann
Summary: The number of scientific investigations on women's football specific to the topics of player characteristics and demands of the game has considerably increased in recent years due to the increased popularity of the women's game worldwide, although they are not yet as numerous as in the case of men's football. To date, only two scientific publications have attempted to review the main findings of studies published in this area. However, one of them was published about 20 years ago, when women's football was still in its infancy and there were only a few studies to report on. The other review was more recent. Nonetheless, its main focus was on the game and training demands of senior elite female players. Thus, information on female footballers of lower competitive levels and younger age groups was not included. Consequently, an updated review is needed in this area. The present article therefore aims to provide an overview of a series of studies that have been published so far on the specific characteristics of female football players and the demands of match-play. Mean values reported in the literature for age (12–27 years), body height (155–174 cm), body mass (48–72 kg), percent body fat (13%–29%), maximal oxygen uptake (45.1–55.5 mL/kg/min), Yo-Yo Intermittent Recovery Test Level 1 (780–1379 m), maximum heart rate (189–202 bpm), 30 m sprint times (4.34–4.96 s), and counter-movement jump or vertical jump (28–50 cm) vary mostly according to the players' competitive level and positional role. There are also some special considerations that coaches and other practitioners should be aware of when working with female athletes such as the menstrual cycle, potential pregnancy and lactation, common injury risks (particularly knee and head injuries) and health concerns (e.g., female athlete triad, iron deficiency, and anemia) that may affect players' football performance, health or return to play. Reported mean values for total distance covered (4–13 km), distance covered at high-speed (0.2–1.7 km), average/peak heart rate (74%–87%/94%–99% HRmax), average/peak oxygen uptake (52%–77%/96%–98% VO2max), and blood lactate (2.2–7.3 mmol/L) during women's football match-play vary according to the players' competitive level and positional role. Methodological differences may account for the discrepancy of the reported values as well. Finally, this review also aims to identify literature gaps that require further scientific research in women's football and to derive a few practical recommendations. The information presented in this report provides an objective point of reference about player characteristics and game demands at various levels of women's football, which can help coaches and sport scientists to design more effective training programs and science-based strategies for the further improvement of players' football performance, health, game standards, and positive image of this sport.

#10 Principles and practices of training for soccer
Reference: Journal of Sport and Health Science Volume 3, Issue 4, December 2014, Pages 251–257 doi:10.1016/j.jshs.2014.07.002
Authors: Ryland Morgans, Patrick Orme, Liam Anderson, Barry Drust
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Summary: The complexity of the physical demands of soccer requires the completion of a multi-component training programme. The development, planning, and implementation of such a programme are difficult due partly to the practical constraints related to the competitive schedule at the top level. The effective planning and organisation of training are therefore crucial to the effective delivery of the training stimulus for both individual players and the team. The aim of this article is to provide an overview of the principles of training that can be used to prepare players for the physical demands of soccer. Information relating to periodisation is supported by an outline of the strategies used to deliver the acute training stress in a soccer environment. The importance of monitoring to support the planning process is also reviewed.

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