Latest research in football - week 12 - 2014

Latest research in football

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 The nordic football injury audit: higher injury rates for professional football clubs with third-generation artificial turf at their home venue
Authors: Kristenson K, Bjørneboe J, Waldén M, Andersen T, Ekstrand J, Hägglund M.
Reference: Br J Sports Med. 2014 Apr;48(7):621. doi: 10.1136/bjsports-2014-093494.166.
Summary: Studies generally report similar acute injury rates when playing football on artificial turf (AT) compared with natural grass (NG), but the association between playing surface and overuse injury rates is rarely reported. The objective was to compare (i) acute injury rates in professional football played on AT and NG at the individual player level, and (ii) acute and overuse injury rates at the club level between clubs having AT at their home venue and clubs with NG. All clubs in the Swedish and Norwegian first leagues in seasons 2010 and 2011 were invited to participate. 32/37 clubs participated (AT clubs, n=11; NG clubs, n=21), including 1044 players. Football exposure and injuries on AT vs. NG. Clubs were further defined as AT club or NG club according to the surface installed at their home venue. Injury rate expressed as the number of time loss injuries/1000 hours and reported as a rate ratio (RR) with 99% confidence interval were used as main outcome measures. No differences were found in acute injury rates on AT and NG during match play (RR 0.98, 0.79-1.22) or training (RR 1.14, 0.86-1.50) at individual player level. At club level AT clubs had higher acute training injury rate (RR 1.31, 1.04-1.63), and overuse injury rate (RR 1.38, 1.14-1.65) compared with NG clubs. Consistent with previous research, no differences were seen in acute injury rates when playing on AT compared with NG. However, clubs with AT at their home venue had higher rates of acute training injury and overuse injury compared with clubs that play home matches on NG.

#2 Evaluating influences on classifications of severity for injuries in professional football
Authors: Hammond L, Lilley J, Pope G, Ribbans W.
Reference: Br J Sports Med. 2014 Apr;48(7):604. doi: 10.1136/bjsports-2014-093494.120.
Summary: According to consensus definitions for football surveillance, injury severity is classified from 'slight' to 'career ending', based on number of days absence from participation. The purpose of the study was to examine whether different definitions of return to participation (RTP), and playing in matches while injured, affect groupings of injury severity in professional football. Male professional footballers contracted to a Championship, League 1 and League 2 football team (n=78) participated in the study. 1) RTP, defined as 'return to full participation in training (RTT)' and 'return to match play (RTM)' in 161 injuries. 2) Presence of pain or symptoms that directly preceded or followed time loss, in 45 episodes of playing while injured. Injury severity, measured by the number of days from date of injury to RTP, expressed according to consensus statement severity groupings were used as main outcome measures. Median days absence from participation was significantly higher for RTM than RTT, although this did not affect average severity groupings (z=-8.824, P<.001; RTM: mean 15.7±2.3 days [moderate injury], median 6 days [mild injury]; RTT: mean 10.9±2.2 days [moderate injury], median 4 days [mild injury]). Differences were observed in the distribution of injuries grouped according to their severity with the two definitions of RTP. Two thirds of cases where athletes played in matches while injured were reclassified into higher severity groupings when the time spent playing in matches while injured, either directly preceding or following a period of absence, was counted. When measured in days, football injury severity is directly influenced by definitions of RTP, and may be affected by match scheduling. Pain or injury symptoms do not contribute towards current severity classifications, yet often precede or follow a period of absence. Therefore, expressions of injury severity in football should encompass more than just absence from participation.

#3 Do MRI and ultrasound of the anterior pelvis correlate with, or predict, young football players' clinical findings? A 4-year prospective study of elite academy soccer players
Authors: Robinson P, Grainger AJ, Hensor EM, Batt ME, O'Connor PJ.
Reference: Br J Sports Med. 2014 Mar 6. doi: 10.1136/bjsports-2013-092932. [Epub ahead of print]
Summary: The purpose was to prospectively follow a cohort of elite young male professional soccer players with sequential symptom questionnaires and imaging of the anterior pelvis to determine the prevalence and severity of imaging findings. 34 male athletes (mean age 16.5 years) underwent clinical examination, history/symptom questionnaire, ultrasound and 1.5 T MRI of the anterior pelvis. Athletes then underwent annual questionnaire and ultrasound with MRI also performed every 18 months. Two experienced radiologists scored ultrasound (consensus) and MRI (independently) for abnormality including pubic bone, capsule and tendon oedema and scores correlated with symptoms and presence or absence of previous injuries. Over 4 years the participants fell from 34 to 22 in number with no withdrawals due to groin injury. On study entry no athletes had undergone previous hip or pelvic surgery. On MRI pubic bone oedema, secondary cleft, capsule/tendon oedema and enhancement did not differ substantively between players with and without history of previous injury. κ Analysis for MRI scoring showed excellent agreement (0.84-0.96) for pubic bone marrow oedema, secondary cleft, capsule/tendon oedema and enhancement. On ultrasound inguinal wall motion and adductor tendinopathy did not differ substantively between players with and without history of previous injury. Stability of imaging assessments over time showed no consistent difference. Pubic bone marrow and parasymphyseal findings (cleft, capsule/tendon oedema) on MRI or inguinal canal ballooning on ultrasound were frequently found in asymptomatic athletes and did not predict injury or symptom development.

#4 Muscle injury rates in professional football increase with fixture congestion: an 11-year follow-up of the uefa champions league injury study
Reference: Br J Sports Med. 2014 Apr;48(7):566-7. doi: 10.1136/bjsports-2014-093494.19.
Authors: Bengtsson H, Ekstrand J, Waldén M, Hägglund M.
Summary: The influence of fixture congestion on injury rates and team performance has only been scarcely investigated. The objective was to study associations between match load, recovery days, injury rates and team match performances in professional football. 27 teams, all selected by the UEFA and all competing at the highest level of European football, playing 8 150 competitive matches during the 11-year study period were included. Injury rates and team match performances were compared depending on the number of recovery days between matches using two different cut offs (≤3 vs. >3 days and ≤4 vs. ≥6 days). Match load, injury rates and team match performances were also studied over extended match sequences during the season, each sequence containing five consecutive matches over a mean of 27 days (range 7-104 days). Number of time loss injuries/1000 h of exposure and amount of matches won, lost or drawn were used as main outcome measures.  Team performance showed no association with match load except for Europa League matches that indicated more matches lost with ≤3 days compared with >3 days recovery (P=.048). Total injury rates and muscle injury rates, specifically hamstring and quadriceps injuries, were increased in league matches with ≤4 days compared with ≥6 days recovery preceding the match (rate ratio [RR] 1.09, 95% CI 1.00-1.18, and RR 1.32, 95% CI 1.15-1.51, respectively) while no differences were found when using the other cut off (≤3 vs. >3 days). High match load during a match sequence was associated with an increase in muscle injury rates (P=.012). Fixture congestion was associated with increased muscle injury rates but had no, or very limited, influence on team match performances.

#5 Preparing football referee to manage conflict
Authors: Dell C, Rhind D, Misia G.
Reference: Br J Sports Med. 2014 Apr;48(7):583-4. doi: 10.1136/bjsports-2014-093494.65.
Summary: The number of football referees in the United Kingdom has significantly declined over recent years (The F.A, 2011). Previous research has indicate that conflict is an importnat factor in referees leaving the game and impact on their personal health and wellbeing (Dell, Rhind & Gervis, 2013). This study evaluates a training programme which aims to develop referee's ability to manage conflict during matches. It is intended that this research will inform The F.A.'s drive to retain referees. The aims of the workshop were for the individuals to develop self-awareness of their own referee behaviour; to use conflict management stratergies to help them referee more effectively and to enhance their practical refereeing skills. Trainee referees participated in this study; Group A (experimental) and Group B (control). Both genders were represented (Group A M=19 F=1/Group B M=18 F=2) aged from 14->55 years of age. Group A undertook a new specifically designed conflict managment and resolution workshop for referees as part of their basic referee training course. Group B completed the normal training programme. Both groups completed a pre-workshop questionaire based on their training and how they felt they had dealt with conflict during their 6 training games as a referee. The questionaire employed both likert-type scales and qualitative questions. Upon completion of the training programme both groups completed a post-workshop questionaire. Results from the post-workshop questionnaires for Group A indicate a significant imporvement in their ability to manage conflict relative to Group B. The significance for Group A in managing conflict was still present 3 months later. This workshop has had a direct impact on how referees deal with and handle conflict.

#6 From content to context: the development of the footyfirst program to prevent lower limb injuries in community Australian football
Authors: Donaldson A, Lloyd D, Young W, Barbery G, Cook J, Gabbe B, Finch C.
Reference: Br J Sports Med. 2014 Apr;48(7):587-8. doi: 10.1136/bjsports-2014-093494.76.
Summary: Developing injury prevention programs for community sport is challenging. The injury issues and interventions must be grounded in science and be both meaningful to, and implementable by, those involved in community sport. The This presentation will detail the multi-stage iterative process used to develop FootyFirst, a community-Australian Football (AF) specific lower limb injury prevention program. The scientific literature, clinical experience, expert and end-user consultations, community trials, theory-informed discussion, and graphic design and editorial expertise, were combined to develop FootyFirst. Lower limb injuries were identified as the major injury concern and it was established that a combination of balance and control, eccentric hamstring, plyometric and strength exercises could be efficacious in preventing such injuries. The multi-disciplinary research team used evidence from the scientific literature, clinical experience and knowledge of the community-AF context in an iterative process to create and trial the exercises and progressions that were included in the first draft of FootyFirst. This draft was further refined through a Delphi process in which AF-specific lower limb injury prevention experts agreed on the appropriateness of including the proposed exercises in FootyFirst. Potential end-user groups (community-AF players, coaches, fitness coaches, sports trainers and administrators) provided feedback about the fit between FootyFirst and the implementation context including potential barriers and facilitators to widespread program adoption and implementation. Trials of FootyFirst were conducted to ensure it could be understood and delivered by community-AF coaches and completed by players. The research team then reviewed the entire program during discussions focused around the Diffusion of Innovations principles of relative advantage, compatibility, complexity, trialability and observability before expert graphic designers and editors were engaged to develop FootyFirst resources. The content-to-context process detailed in this presentation was successfully used to develop FootyFirst, an evidence-informed, expert-endorsed, context-specific community-AF lower limb injury prevention program.

#7 Differences in injury risk and characteristics between Dutch amateur and professional soccer players
Authors: van Beijsterveldt AM, Stubbe JH, Schmikli SL, van de Port IG, Backx FJ
Reference: J Sci Med Sport. 2014 Feb 9. pii: S1440-2440(14)00032-2. doi: 10.1016/j.jsams.2014.02.004. [Epub ahead of print]
Summary: To compare the incidence and characteristics of injuries between Dutch amateur and professional male soccer players during one entire competition season. During the 2009-2010 season, 456 Dutch male amateur soccer players and 217 professional players were prospectively followed. Information on injuries and individual exposure to all soccer activities were recorded in both cohorts. Injuries were recorded using the time-loss definition. In total, 424 injuries were recorded among 274 of the amateur players (60.1% injured players) and 286 injuries were sustained by 136 (62.7% injured players) of the professional players (p=0.52). Compared to the professionals, the injury incidence during training sessions was higher among amateurs (p=0.01), but the injury incidence among professionals was higher during matches (p<0.001). Professional players also had a higher incidence of minimal injuries (p<0.001), whereas the incidence of moderate and severe injuries was higher for amateurs (all p<0.001). Lastly, professional players sustained more overuse injuries (p=0.02), whereas amateurs reported more recurrent injuries (p<0.001). The above-mentioned differences in injury rates between amateur and professional players in the Netherlands might be explained by the difference in the level at which they play, since factors like the availability of medical support and/or the team size may influence the injury risk and characteristics.

#8 Executive functioning in highly talented soccer players
Authors: Verburgh L, Scherder EJ, van Lange PA, Oosterlaan J.
Reference: PLoS One. 2014 Mar 14;9(3):e91254. doi: 10.1371/journal.pone.0091254. eCollection 2014.
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Summary: 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.

#9 Biomechanical and functional indicators in male semiprofessional soccer players with increased hip alpha angles vs. amateur soccer players
Authors: Lahner M, von Schulze Pellengahr C, Walter PA, Lukas C, Falarzik A, Daniilidis K, von Engelhardt LV, Abraham C, Hennig EM, Hagen M.
Reference: BMC Musculoskelet Disord. 2014 Mar 16;15(1):88. doi: 10.1186/1471-2474-15-88.
Summary: Femoroacetabular impingement (FAI) is predominant in young male athletes, but not much is known about gait differences in cases of increased hip alpha angles. In our study, the hip alpha angle of Nötzli of soccer players was quantified on the basis of magnetic resonance imaging (MRI) with axial oblique sequences. The aim of the current study was to compare the rearfoot motion and plantar pressure in male semiprofessional soccer players with increased alpha angles to age-matched amateur soccer players. In a prospective analysis, male semiprofessional and amateur soccer players had an MRI of the right hip to measure the alpha angle of Nötzli. In a biomechanical laboratory setting, 14 of these participants in each group ran in two shoe conditions. Simultaneously in-shoe pressure distribution, tibial acceleration, and rearfoot motion measurements of the right foot were performed. In the semiprofessional soccer group, the mean value of the alpha angle of group was 55.1 ± 6.58° (range 43.2-76.6°) and 51.6 ± 4.43° (range 41.9-58.8°) in the amateur group. In both shoe conditions, we found a significant difference between the two groups concerning the ground reaction forces, tibial acceleration, rearfoot motion and plantar pressure parameters (P < 0.01, P < 0.05, P = 0.04). Maximum rearfoot motion is about 22% lower in the semiprofessional group compared to the amateur group in both shoe conditions. This study confirmed that semiprofessional soccer players with increased alpha angles showed differences in gait kinematics compared to the amateur group. These findings support the need for a screening program for competitive soccer players. In cases of a conspicuous gait analysis and symptomatic hip pain, FAI must be ruled out by further diagnostic tests.

#10 Effects of a contrast training program without external load on vertical jump, kicking speed, sprint and agility of young soccer players
Reference: J Strength Cond Res. 2014 Mar 11. [Epub ahead of print]
Authors: García-Pinillos F, Martínez-Amat A, Hita-Contreras F, Martínez-López EJ, Latorre-Román PA.
Summary: The purpose of this study was to determine the effects of a twelve-week contrast training (CT) program (isometric + plyometric), with no external loads, on the vertical jump, kicking speed, sprinting, and agility skills of young soccer players. Thirty young soccer players (age: 15.9 ± 1.43 years; weight: 65.4 ± 10.84 kg; height: 171.0 ± 0.06 cm) were randomized in a control group (n = 13) and an experimental group (n = 17). The CT program was included in the experimental group's training sessions, who undertook it twice a week as a part of their usual weekly training regime. This program included three exercises: one isometric and two plyometric, without external loads. These exercises progressed in volume throughout the training program. Performance in countermovement jump (CMJ), Balsom agility test (BAT), 5-, 10-, 20- and 30-meter sprint, and soccer kick were assessed before and after the training program. A two-factor (group and time) analysis of variance revealed significant improvements (p < 0.001) in CMJ, BAT, and kicking speed in the experimental group players. Control group remained unchanged in these variables. Both groups significantly reduced sprint times over 5, 10, 20 and 30 meters (p < 0.05). A significant correlation (r = 0.492, p < 0.001) was revealed between [INCREMENT]BAT and [INCREMENT]Average-Kicking-Speed. Results suggest that a specific CT program without external loads is effective for improving soccer specific skills such as vertical jump, sprint, agility, and kicking speed in young soccer players.

#11 Practical experience with the implementation of an athlete's biological profile in athletics, cycling, football and swimming
Reference: Br J Sports Med. 2014 Mar 19. doi: 10.1136/bjsports-2014-093567. [Epub ahead of print]
Authors: Zorzoli M, Pipe A, Garnier PY, Vouillamoz M, Dvorak J.
Summary: The introduction of the athlete's biological passport (ABP) has been a milestone in the fight against doping. The ABP is a collection of measurements of different biological parameters influenced by the administration of doping agents through the time and for each athlete. Two different modules have been developed and validated so far: the haematological module, which aims to identify enhancement of oxygen transport, including use of erythropoiesis-stimulating agents and any form of blood transfusion or manipulation, which became effective in 2010; and the steroidal module, which intends to detect the use of endogenous anabolic androgenic steroids when administered exogenously and other anabolic agents, which was introduced in 2014. Prior to the implementation of the haematological module, it is important to define an athlete's testing pool on whom to collect blood and/or urine in-competition and out-of-competition (for the steroidal module, this is irrelevant because all collected urine samples will be subjected to analysis for the steroidal variables) and to be compliant with the strict requirements of the World Anti-Doping Agency ABP Operating Guidelines. The established individual profile can be used either to target traditional antidoping tests (recombinant erythropoietins, or homologous blood transfusion tests for the haematological module; isotope ratio mass spectrometry (IRMS) for the steroidal module) or to support an antidoping rule violation due to the use of a forbidden substance or method. In this article, we present the experience of four major International Federations which have implemented an ABP programme, focusing on the haematological module. They constitute examples which could be followed by other antidoping organisations wishing to introduce this new, efficient and innovative antidoping tool.

#12 Aerobic Fitness Ecological Validity in Elite Soccer Players: A Metabolic Power Approach
Reference: Journal of Strength & Conditioning Research: April 2014 - Volume 28 - Issue 4 - p 914–919
doi: 10.1519/JSC.0000000000000239
Authors: Manzi V, Impellizzeri F, Castagna C
Summary: The aim of this study was to examine the association between match metabolic power (MP) categories and aerobic fitness in elite-level male soccer players. Seventeen male professional soccer players were tested for V[Combining Dot Above]O2max, maximal aerobic speed (MAS), V[Combining Dot Above]O2 at ventilatory threshold (V[Combining Dot Above]O2VT and %V[Combining Dot Above]O2VT), and speed at a selected blood lactate concentration (4 mmol·L−1, VL4). Aerobic fitness tests were performed at the end of preseason and after 12 and 24 weeks during the championship. Aerobic fitness and MP variables were considered as mean of all seasonal testing and of 16 Championship home matches for all the calculations, respectively. Results showed that V[Combining Dot Above]O2max (from 0.55 to 0.68), MAS (from 0.52 to 0.72), V[Combining Dot Above]O2VT (from 0.72 to 0.83), %V[Combining Dot Above]O2maxVT (from 0.62 to 0.65), and VL4 (from 0.56 to 0.73) were significantly (p < 0.05 to 0.001) large to very large associated with MP variables. These results provide evidence to the ecological validity of aerobic fitness in male professional soccer. Strength and conditioning professionals should consider aerobic fitness in their training program when dealing with professional male soccer players. The MP method resulted an interesting approach for tracking external load in male professional soccer players.

#13 Relationships Between Field Performance Tests in High-Level Soccer Players
Reference: Journal of Strength & Conditioning Research: April 2014 - Volume 28 - Issue 4 - p 942–949
doi: 10.1519/JSC.0b013e3182a1f861
Authors: Ingebrigtsen J, Brochmann M, Castagna C, Bradley P, Ade J, Krustrup P, Holtermann A
Summary: To reduce athlete testing time, the aim of this study was to investigate the relationship between the Yo-Yo intermittent recovery test levels 1 (IR1) and 2 (IR2) performances, maximal sprinting speed (10, 20, and 35 m), repeated sprint ability (RSA; 7 × 35 m), and submaximal heart rates (HRs) after 2 and 4 minutes of the Yo-Yo IR tests by testing 57 high-level soccer players. All players played regularly in one of 3 highest levels of Norwegian soccer and were tested during 3 sessions on 3 consecutive days. Large correlations were observed between Yo-Yo IR1 and IR2 test performances (r = 0.753, p ≤ 0.05). Small and moderate correlations were found between 20- and 35-m sprinting speed and Yo-Yo IR1 performance (r = −0.289 and −0.321, respectively, p ≤ 0.05), whereas 35-m sprinting speed correlated moderately to Yo-Yo IR2 performance (r = −0.371, p ≤ 0.05). Repeated sprint ability at 10, 20, and 35 m all showed moderate to large correlations to Yo-Yo IR1 performance (r = −0.337 to −0.573, p ≤ 0.05). Repeated sprint ability at 20 m (r = −0.348, p ≤ 0.05) and 35 m (r = −0.552, p ≤ 0.01) correlated moderately and largely to Yo-Yo IR2 performance. In addition, moderate and large correlations were found between submaximal Yo-Yo IR1 HRs after 2 (r = −0.483, p ≤ 0.01) and 4 minutes (r = −0.655, p ≤ 0.01) and Yo-Yo IR1 performance, and 2 minutes Yo-Yo IR2 HR and Yo-Yo IR2 performance (r = −0.530, p ≤ 0.01). Intraclass correlation measures of submaximal HR after 2 and 4 minutes of Yo-Yo IR1 test and after 2 minutes of the Yo-Yo IR2 were 0.92 (coefficient of variation [CV] = 4.1%, n = 33), 0.93 (CV = 3.8%, n = 33), and 0.72 (CV = 2.9%, n = 10). Adjusted ordinary least square (OLS) regressions revealed associations (p ≤ 0.05) between sprint speed at 20 and 35 m and Yo-Yo IR1 test performance, but only between 35 m and IR2 test performance (p ≤ 0.05). Further, OLS showed that RSA at 35 m was related to both levels of the Yo-Yo IR test (p ≤ 0.01), and that submaximal HRs after 2 and 4 minutes were independently associated with Yo-Yo IR1 and IR2 performances (p ≤ 0.01). In conclusion, Yo-Yo IR1 and 2 test performances, as well as sprint and RSA performances, correlated very largely, and it may therefore be considered using only one of the Yo-Yo tests and a RSA test, in a general soccer-specific field test protocol. The submaximal HR measures during Yo-Yo tests are reproducible and may be used for frequent, time-efficient, and nonexhaustive testing of intermittent exercise capacity of high-level soccer players.

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