Latest research in football - week 48 - 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 Injury incidence in a Premier League youth soccer academy using the consensus statement: a prospective cohort study
Reference: BMJ Open Sport Exerc Med. 2016 Oct 26;2(1):e000132. eCollection 2016.
Authors: Renshaw A, Goodwin PC
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Summary: There is an established risk of injury to young athletes exposed to high training loads. Identifying and monitoring injury risk is essential to aid prevention. The aim of this study was to use the consensus statement to determine the incidence and pattern of injury in 1 English Premier League soccer academy during 1 season. A prospective cohort study included 181 elite academy soccer players during the 2012-2013 season. Players were divided into 5 age groups between 9 and 18 years. The number, type and incidence of injuries were recorded during matches and training. Incidence was calculated per 1000 hours of exposure. 127 injuries occurred during 29 346 hours of soccer exposure. 72% of injuries were non-contact related. Under (U)18 players sustained the highest number of match injuries. U12-14 players sustained the highest number of training injuries and injuries overall. U16 players sustained the highest number of severe injuries, and U18 players sustained the highest number of moderate injuries. U18 players sustained the highest number of injuries/1000 hours of training and overall. U15 players sustained the highest number of injuries/1000 hours of matches, the highest number of recurrent injuries and the highest incidence of recurrence. The most common injuries were muscle injuries in U15 and U18 players. The most common injury location was the anterior thigh, with the majority of these occurring in training. Using the consensus statement, this study used a repeatable method to identify the injury profile of elite academy-level soccer players.

#2 Injury prevention exercise programmes in professional youth soccer: understanding the perceptions of programme deliverers
Reference: BMJ Open Sport Exerc Med. 2016 Jan 4;2(1):e000075. eCollection 2016.
Authors: O'Brien J, Finch CF
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Summary: There are well-known challenges to implementing injury prevention strategies in amateur soccer, but information from other soccer settings is scarce. This cross-sectional survey analysed the injury prevention perceptions of soccer coaches, fitness coaches and physiotherapists from 4 male teams in a professional youth soccer academy. The respondents (n=18) completed a web-based survey relating to lower limb (LL) soccer injuries, the value and practicality of injury prevention exercise programmes (IPEPs) in general and, more specifically, the IPEP endorsed by FIFA, the FIFA 11+. There were very high levels of agreement regarding players' susceptibility to LL injury and the seriousness of these injuries. Respondents agreed unanimously that players should perform evidence-based injury prevention exercises. Despite 61% of respondents having previously heard of the FIFA 11+, just 6% reported current use of the full programme, with a further 22% reporting modified use. 22% believed the FIFA 11+ contained adequate variation and progression for their team and 78% felt it needed improvement. Respondents identified multiple barriers and facilitators to maintaining IPEPs, relating either to the programme content (eg, exercise variation), or the delivery and support of the programme (eg, coach acceptance). The coaches, fitness coaches and physiotherapists of professional youth teams support the use of IPEPs, but enhancing their impact requires tailoring of programme content, along with adequate delivery and support at multiple levels. The findings suggest that the FIFA 11+ needs modification for use in professional youth soccer teams.

#3 Concurrent validity of the Gyko inertial sensor system for the assessment of vertical jump height in female sub-elite youth soccer players
Reference: BMC Sports Sci Med Rehabil. 2016 Nov 11;8:35. eCollection 2016.
Authors: Lesinski M, Muehlbauer T, Granacher U
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Summary: The aim of the present study was to verify concurrent validity of the Gyko inertial sensor system for the assessment of vertical jump height. Nineteen female sub-elite youth soccer players (mean age: 14.7 ± 0.6 years) performed three trials of countermovement (CMJ) and squat jumps (SJ), respectively. Maximal vertical jump height was simultaneously quantified with the Gyko system, a Kistler force-plate (i.e., gold standard), and another criterion device that is frequently used in the field, the Optojump system. Compared to the force-plate, the Gyko system determined significant systematic bias for mean CMJ (-0.66 cm, p < 0.01, d = 1.41) and mean SJ (-0.91 cm, p < 0.01, d  = 1.69) height. Random bias was ± 3.2 cm for CMJ and ± 4.0 cm for SJ height and intraclass correlation coefficients (ICCs) were "excellent" (ICC = 0.87 for CMJ and 0.81 for SJ). Compared to the Optojump device, the Gyko system detected a significant systematic bias for mean CMJ (0.55 cm, p < 0.05, d = 0.94) but not for mean SJ (0.39 cm) height. Random bias was ± 3.3 cm for CMJ and ± 4.2 cm for SJ height and ICC values were "excellent" (ICC = 0.86 for CMJ and 0.82 for SJ). Consequently, apparatus specific regression equations were provided to estimate true vertical jump height for the Kistler force-plate and the Optojump device from Gyko-derived data. Our findings indicate that the Gyko system cannot be used interchangeably with a Kistler force-plate and the Optojump device in trained individuals. It is suggested that practitioners apply the correction equations to estimate vertical jump height for the force-plate and the Optojump system from Gyko-derived data.

#4 Effect of oxygen therapy on myocardial salvage in ST elevation myocardial infarction: the randomized SOCCER trial
Reference: Eur J Emerg Med. 2016 Nov 23. [Epub ahead of print]
Authors: Khoshnood A, Carlsson M, Akbarzadeh M, Bhiladvala P, Roijer A, Nordlund D, Höglund P, Zughaft D, Todorova L, Mokhtari A, Arheden H, Erlinge D, Ekelund U.
Summary: Recent studies suggest that administration of O2 in patients with acute myocardial infarction may have negative effects. With the use of cardiac MRI (CMR), we evaluated the effects of supplemental O2 in patients with ST elevation myocardial infarction (STEMI) accepted for acute percutaneous coronary intervention (PCI). This study was a randomized-controlled trial conducted at two university hospitals in Sweden. Normoxic STEMI patients were randomized in the ambulance to either supplemental O2 (10 l/min) or room air until the conclusion of the PCI. CMR was performed 2-6 days after the inclusion. The primary endpoint was the myocardial salvage index assessed by CMR. The secondary endpoints included infarct size and myocardium at risk. At inclusion, the O2 (n=46) and air (n=49) patient groups had similar patient characteristics. There were no significant differences in myocardial salvage index [53.9±25.1 vs. 49.3±24.0%; 95% confidence interval (CI): -5.4 to 14.6], myocardium at risk (31.9±10.0% of the left ventricle in the O2 group vs. 30.0±11.8% in the air group; 95% CI: -2.6 to 6.3), or infarct size (15.6±10.4% of the left ventricle vs. 16.0±11.0%; 95% CI: -4.7 to 4.1). In STEMI patients undergoing acute PCI, we found no effect of high-flow oxygen compared with room air on the size of ischemia before PCI, myocardial salvage, or the resulting infarct size. These results support the safety of withholding supplemental oxygen in normoxic STEMI patients.

#5 Effects of Sprint Training With and Without Weighted Vest on Speed and Repeated Sprint Ability in Male Soccer Players
Reference: J Strength Cond Res. 2016 Nov 16. [Epub ahead of print]
Authors: Rey E, Padrón-Cabo A, Fernández-Penedo D
Summary: The purpose of this study was to assess the effect resisted sprint training using weighted vests (WV) compared with unresisted sprint training (US) on physical fitness (countermovement jump, 10 m sprint, 30 m sprint and repeated sprint ability (RSA)) in amateur male soccer players. 19 soccer players (age: 23.7±4.5 years; height: 178.3±5.8 cm; body mass: 72.9±5.2 kg) were randomly assigned to a WV (n= 10) or a US (n= 9) group. The intervention program had to be carried out 2 times a week over 6 weeks. The only difference between the two interventions was that the WV group performed all the sprints with an additional weight of 18.9% ± 2.1% of body mass. Within-group analysis showed significant improvements (p<0.001) in 10 m and 30 m sprint performance from pretest to post-test in WB (+9.42% and +6.04%) and CTU (+10.87% and +5.10%). Players in both WV and US also showed significant enhancements in RSA average time, fastest time, and total time from pretest to posttest. Percentage changes in 30 m sprint performance, for both groups combined, had a very large correlation with percentage changes in average time of RSA. In the between-groups analysis, there were no differences between the sprint training groups (WV vs US) in any variable. In conclusion, the findings of this study indicate that both sprint training methods used seem to be effective to improve soccer related performance measures, and could be beneficial to players and coaches in field settings.

#6 Leg Stiffness In Female Soccer Players: Inter-Session Reliability And The Fatiguing Effects Of Soccer-Specific Exercise
Reference: J Strength Cond Res. 2016 Nov 16. [Epub ahead of print]
Authors: De Ste Croix M, Hughes J, Lloyd RS, Oliver JL, Read P
Summary: Low levels of leg stiffness and reduced leg stiffness when fatigue is present compromise physical performance and increase injury risk. The purpose of this study was to (a) determine the reliability of leg stiffness measures obtained from contact mat data and (b) explore age-related differences in leg stiffness following exposure to a soccer-specific fatigue protocol in young female soccer players. 37 uninjured female youth soccer players divided into 3 sub-groups based on chronological age (U13, U15 and U17 year olds) volunteered to participate in the study. Following baseline data collection during which relative leg stiffness, contact time, flight time was collected, participants completed an age-appropriate soccer-specific fatigue protocol (SAFT). Upon completion of the fatigue protocol, subjects were immediately re-tested. Inter-session reliability was acceptable and could be considered capable of detecting worthwhile changes in performance. Results showed that leg stiffness decreased in the U13 year olds, was maintained in the U15 age group and increased in the U17 players. Contact times and flight times did not change in the U13 and U15 year olds, but significantly decreased and increased respectively in the U17 age group. The data suggests that age-related changes in the neuromuscular control of leg stiffness are present in youth female soccer players. Practitioners should be aware of these discrepancies in neuromuscular responses to soccer-specific fatigue, and should tailor training programs to meet the needs of individuals which may subsequently enhance performance and reduce injury risk.

#7 A topography of free kicks in soccer
Reference: J Sports Sci. 2016 Dec;34(24):2312-2320.
Authors: Link D, Kolbinger O, Weber H, Stöckl M
Summary: This study investigates the spatial relationship of performance variables for soccer free kicks. In order to suggest ways in which players might optimise their performance, we collected data from free kicks (<35 m to goal line) of two German Bundesliga seasons (2013/14, 2014/15) (n = 1624). In the analysis, we applied the ISO-map approach using colour gradients to visualise the mean values of a variable on a 2D-map of the pitch. Additionally, variograms were used to describe the degree of spatial dependence of the free kick variables. Results show that DENSITY, TYPE OF PLAY, PLAYERS IN WALL, DISTANCE TO WALL and RULE VIOLATION were strongly spatially dependent. Centrality and proximity to the goal increased the variables PLAYERS IN WALL, RULE VIOLATIONS and INTERRUPTION TIME, and the ratio of goals scored increased from 5.9% (central far) to 10.9% (central near). In 70.9% of the shots, players preferred a switched laterality, which did not result in a higher success rate. Furthermore, there was no statistical advantage for the defensive team when DISTANCE TO WALL was below 9.15 m or when there was a RULE VIOLATION. Crosses had a success rate (i.e., first controlled ball contact after the cross) of 20.8%. Played with natural laterality, they were 5% more successful than with switched laterality. Crosses from the right side outside the penalty box were 10% more successful than from the left side. Therefore, it might be worthwhile practising the defence of balls coming from this side.

#8 Endoscopic debridement and fibrin glue injection of a chronic Morel-Lavallée lesion of the knee in a professional soccer player: A case report and literature review
Reference: Knee. 2016 Nov 22. pii: S0968-0160(16)30183-1. doi: 10.1016/j.knee.2016.10.017. [Epub ahead of print]
Authors: Koc BB, Somorjai N, P M Kiesouw E, Vanderdood K, Meesters-Caberg M, Draijer FW, Jansen EJ
Summary: A Morel-Lavallée lesion is a post-traumatic closed degloving injury of soft tissue. The lesion is due to a shearing trauma with separation of subcutaneous tissue from underlying fascia. When conservative treatment fails, surgical treatment is imperative. Commonly, open drainage and debridement is performed. This case report describes a Morel-Lavallée lesion of the knee in a professional soccer player who was successfully treated with endoscopic debridement and fibrin glue injection after failure of conservative management. This method achieves the goal of an open surgical debridement without exposing patients to an increased morbidity.

#9 Symptoms and risk factors of depression during and after the football career of elite female players
Reference: BMJ Open Sport Exerc Med. 2016 May 31;2(1):e000124. eCollection 2016.
Authors: Prinz B, Dvořák J, Junge A
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Summary: The mental health of elite athletes has received increasing attention in recent years, but no study has evaluated the career-time prevalence of depression, and very few have analysed risk factors of mental health problems during or after the career. 157 (response rate 64.1%) female players who played in the German First League answered an anonymous online survey on details of their football career, stressful and helpful conditions, depression and need of psychotherapeutic support during and after the football career. The career-time prevalence of depression symptoms was 32.3%. Significant differences in the average depression score were observed for playing positions (F=2.75; p<0.05) and levels of play (F=3.53; p<0.01). About half of the players (49.7%) stated 'conflicts with coach/management' as an important reason for their low in moods, followed by 'low in performance/injury' (48.4%) and 'too little support/acknowledgement by the coach' (40.0%). 'Psychological strain/stress' (46.5%) was (after injury) the second most important reason for lows in performance. During their career, almost 40% of players wanted or needed psychological support, but only 10% received it. After their career, the percentage of players wanting or needing psychological support decreased to 24%, of whom 90% received it. The high prevalence of depression symptoms in combination with low use of psychotherapy during the career shows the need for de-stigmatisation of mental health issues in elite football. Furthermore, it seems very important to educate coaches, physicians, physiotherapists and club managers to recognise and prevent mental health problems of their players.

#10 Prevalence of depression and anxiety in top-level male and female football players
Reference: BMJ Open Sport Exerc Med. 2016 Jan 19;2(1):e000087. eCollection 2016.
Authors: Junge A, Feddermann-Demont N
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Summary: Scientific studies on the prevalence of mental health problems in elite athletes are rare, and most have had considerable methodological limitations, such as low response rate and heterogeneous samples. The aim of the study was to evaluate the prevalence of depression and anxiety in top-level football players in comparison to the general population, and to analyse potential risk factors. Players of all first league (FL) and of four U-21 football teams in Switzerland were asked to answer a questionnaire on player's characteristics, the Centre of Epidemiologic Studies Depression Scale (CES-D) and the Generalized Anxiety Disorder (GAD-7) scale. All 10 women's FL teams, 9 of 10 men's FL teams and 4 male U-21 teams (n=471 football players) took part in the study. The CES-D score indicated a mild to moderate depression in 33 (7.6%) players and a major depression in 13 (3.0%) players. The GAD-7 score indicated an at least moderate anxiety disorder in 6 (1.4%) players. Compared to the general population, the prevalence of depression was similar and the prevalence of anxiety disorders was significantly (χ2=16.7; p<0.001) lower in football players. Significant differences were observed with regard to player characteristics, such as age, gender, player position, level of play and current injury. Swiss FL football players had the same prevalence of depression as the general population, while male U-21 players had a higher prevalence of depression. It is important to raise awareness and knowledge of athletes' mental health problems in coaches and team physicians, and to provide adequate treatment to athletes.

#11 Sympathetic enhancement in futsal players but not in football players after repeated sprint ability test
Reference: BMJ Open Sport Exerc Med. 2015 Nov 27;1(1):e000049. eCollection 2015.
Authors: Chen YS, Liao CJ, Lu WA, Kuo CD
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Summary: Heart rate variability (HRV) can disclose the specific adaptation of sympathovagal modulation to exercise. This study investigated the change in HRV measures after anaerobic and aerobic intermittent exercises in university football and futsal players. 36 male university students with physically active lifestyle (n=14), football (n=12), and futsal (n=10) participated in this study. The participants completed the repeated sprint ability (RSA) test and Yo-Yo (YY) intermittent recovery test level 1 in randomised order. ECG signals of the participants were recorded in supine position 15 min before and 30 min after exercises. Before exercise, and 5 and 30 min after exercise, the blood pressures were also taken. In the RSA protocol, the percentage changes in normalised high-frequency power (nHFP) were significantly decreased, while the percentage changes in the very low/high frequency power ratio (VLHR) and low/high frequency power ratio (LHR) were significantly increased in futsal players after exercise, as compared with the controls. No significant changes in all HRV indices were found in the YY protocol, except the respiratory frequency. After exercise, the percent decrease in vagal modulation in futsal players was significantly reduced, while the percentage increase in sympathetic modulation in futsal players was significantly enhanced in the RSA test, but not in the YY test, as compared with the control group. The increase in sympathetic activity and the decrease in vagal activity in the futsal players were greater than the corresponding increase and decrease in the football players in the RSA test.

#12 Heart Rate, Technical Performance And Session-Rpe In Elite Youth Soccer Small-Sided Games Played With Wildcard Player
Reference: J Strength Cond Res. 2016 Nov 19. [Epub ahead of print]
Authors: Sanchez-Sanchez J, Hernández D, Casamichana D, Martínez-Salazar C, Ramirez-Campillo R, Sampaio J
Summary: The aim of this study was to compare heart rate (HR), perceived exertion (RPE) and technical-tactical actions during small-sided games (SSG) played without (CTR), with internal (IW) and with IW and external (IEW) wildcard players. A total of 22 young male soccer players (age 17.2±0.9 y) randomly completed six 4vs4 SSG situations. The control conditions occurred with goals scored without goalkeeper (4vs4-NO) and with goalkeeper (4vs4-GK). During the experimental conditions the situations incorporated 2 IW (4vs4+2IW-NO, 4vs4+2IW-GK) and 2 IEW (4vs4+2IW+2IEW-NO, 4vs4+2IW+2IEW-GK). Processed results did not included data from goalkeepers, IW and IEW players. The HR was divided in intensity-zones (Z1, Z2 and Z3, for <80%, 80-90% and >90% of maximal HR, respectively) and the analyzed technical-tactical actions were the pass, dribbling, collective success and pause. The effects of IW and IEW were analyzed thought repeated-measures ANOVA. During 4vs4+2IW+2IEW-NO greater time was recorded in Z1 (p<0.05) compared to 4vs4-NO and 4s4+2IW-NO. During 4vs4+2IW+2IEW-GK greater time was recorded in Z1 and less in Z3 (p<0.05) compared to 4vs4-GK. Greater RPE was reported in 4vs4-NO (p<0.01) and 4vs4+2IW-NO (p<0.01) compared to 4vs4+2IW+2IEW-NO, and during 4vs4-GK (p<0.01) than 4vs4+2IW+2IEW-GK. Greater number of dribbling situations were recorded during 4vs4-NO (p<0.05) compared to 4vs4+2IW+2IEW-NO. In conclusion, compared to the control condition of 4vs4, the incorporation of IEW reduced HR, RPE and dribbling actions.

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