Latest research in football - week 41 - 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 Effects of Muscle Fatigue Induced by CMJ on Efficacy Parameters of Instep Ball Kicking in Soccer
Reference: J Appl Biomech. 2016 Oct 13:1-24. [Epub ahead of print]
Authors: Torreblanca-Martínez V, Otero-Saborido FM, González-Jurado JA
Summary: The purpose was to study the effects of muscle fatigue induced by countermovement jumps (CMJ) on instep kick foot velocity in young male soccer players. Fifteen under-18 soccer players of a professional club, performed maximal velocity instep kicks before and after a fatigue protocol that consisted of continuous CMJ (countermovement jump). Foot velocity at impact without fatigue, foot velocity at impact with fatigue, CMJ height without fatigue, maximum jump height in fatigue test, and CMJ height change in fatigue test on a dynamometric platform, were measured. There was a significant difference between jump height with and without fatigue (p = 0.00; ES = 0.8), but there were no significant differences between kicking with fatigue and without fatigue (p = 0.580, ES = 0.10). In conclusion, although the protocol was intense enough to generate fatigue in the muscles involved in CMJ, there were no significant differences in kicking velocity under fatigue conditions with respect to kicking without fatigue in the soccer players studied.

#2 Dynamic balance ability in young elite soccer players: implication of isometric strength
Reference: J Sports Med Phys Fitness. 2016 Oct 11. [Epub ahead of print]
Authors: Chtara M, Rouissi M, Bragazzi NL, Owen AL, Haddad M, Chamari K
Summary: Soccer requires maintaining unilateral balance when executing movement with the contralateral leg. Despite the fact that balance requires standing with maintaining isometric posture with the support leg, currently there is a lack of studies regarding the implication of isometric strength on dynamic balance's performance among young soccer players. Therefore, the aim of this study was to examine the relationship between the Y- balance test and 12 lower limbs isometric strength tests. 26 right footed soccer players (mean±SD, age=16.2±1.6 years, height=175±4.2 cm, body mass = 68.8±6.1 kg) performed a dynamic balance test (star excursion balance-test [SEBT] with dominant- (DL) and nondominant-legs (NDL). Furthermore, maximal isometric contraction tests of 12 lower limb muscle groups were assessed in DL and NDL. Correlations analysis reported a significant positive relationship between some of isometric strength tests (with DL and NDL) and the Y-balance test. Furthermore, stepwise multiple regression analysis showed that maximal isometric strength explained between 21.9% and 49.4% of the variance of the Y-balance test. Moreover, maximal isometric strength was dependent upon the reaching angle of the Y-balance test and the leg used to support body weight. This study showed a significant implication of maximal isometric strength of the lower limb and the Y-balance test. Moreover, the present investigation suggests the implementation of specific lower limb strengthening exercises depending on players' deficit in each reaching direction and leg. This result suggests that further studies should experiment if increasing lower limbs isometric strength could improve dynamic balance ability among young soccer players.

#3 Health problems in former elite female football players: Prevalence and risk factors
Reference: Scand J Med Sci Sports. 2016 Oct 17. doi: 10.1111/sms.12747. [Epub ahead of print]
Authors: Prien A, Prinz B, Dvořák J, Junge A
Summary: The aim of this study was to assess the prevalence of health problems and associated risk factors in former elite female football players. A cross-sectional research design was employed, using an online questionnaire on personal characteristics and health complaints during/after the career. One hundred fifty-two (response rate: 62.0%) former first German league players answered the survey. Around 70% described their current health as good or very good. Over half (57.9%) reported knee problems during the last 4 weeks while exercising and a third (33.6%) during normal daily activities. The second most common location for complaints was the head (53.3%). Almost one quarter (23.7%) of players suffered from osteoarthritis (OA). Regression analysis showed that OA in knee/ankle and physical complaints (PC) in knee/ankle/head were significantly predicted by number and severity of previous injuries (P < 0.05). Further, increases in age, training volume, and level of play were associated with an increased likelihood of presenting with OA (P < 0.05), but not PC. In conclusion, a football career may lead to specific long-term health problems in elite female players. Prevention strategies should focus on knee, ankle, and head injuries. Future studies are needed to clinically assess the prevalence rates of OA and possible neurocognitive changes.

#4 The efficacy of exercise in preventing injury in adult male football: a systematic review of randomised controlled trials
Reference: Sports Med Open. 2015 Dec;1(1):4. Epub 2015 Jan 20.
Authors: Porter T, Rushton A
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Summary: Injury prevention measures might reduce the impact of injury on footballers and football clubs. Increasing research has evaluated the use of exercise for injury prevention. However, research has focused on adolescent females. No high-quality systematic reviews have evaluated the efficacy of all forms of exercise on preventing injury in adult male football. Our objective was to conduct a systematic review to evaluate the efficacy of exercise in preventing injury in adult male football. Comprehensive searches of electronic databases CINAHL (Cumulative Index to Nursing and Allied Health Literature), MEDLINE, Embase, AMED (The Allied and Complementary Medicine Database), the Cochrane Central Register of Controlled Trials, PEDro (The Physiotherapy Evidence Database), SPORTDiscus™, the National Research Register, Current Controlled Trials website (York), and were conducted using predefined search terms to identify relevant studies published up to 1 March 2013. Screening of references, searches of grey literature, and hand searches of relevant journals were also employed. Included studies were randomized controlled trials using injury incidence as an outcome measure to evaluate the efficacy of an exercise intervention on uninjured male footballers aged 16 years and over. Articles not written in English were excluded. Two researchers independently searched data sources, screened studies for eligibility, evaluated risk of bias, and extracted data using predefined criteria. Risk of bias of included trials was assessed using the Cochrane Collaboration's tool for assessing risk of bias. There was insufficient trial comparability (outcome measures, interventions, injury type) for meta-analysis, and a qualitative analysis was performed. Eight trials (n = 3,355) from five countries met the inclusion criteria. All trials were assessed as having a high risk of bias. Two trials reported statistically significant reductions in hamstring injuries with eccentric exercise, and two reported statistically significant reductions in recurrent ankle sprains with proprioceptive exercise. Four trials showed no statistically significant difference in injury incidence with exercise interventions targeting a range of injuries. Notable limitations of included trials included poor reporting and limited blinding. A high risk of bias and insufficient comparability across trials prevented quantitative data synthesis. Limitations in the context of study quality and heterogeneity resulted in an inability to reach a clear conclusion regarding efficacy of exercise for injury prevention in adult male football. Future low risk of bias, properly powered, and comprehensively reported trials are warranted to evaluate the efficacy of exercise on injury prevention. The use of eccentric hamstring exercise for hamstring injury prevention and proprioceptive training for recurrent ankle sprain prevention might be a good focus for future trials, as existing trials with a high risk of bias suggest an effect.

#5 Symptoms of common mental disorders among professional football referees: a one-season prospective study across Europe
Reference: Phys Sportsmed. 2016 Oct 14. [Epub ahead of print]
Authors: Gouttebarge V, Johnson U, Rochcongar P, Rosier P, Kerkhoffs G
Summary: The primary aim of this study was to determine the prevalence and one-season incidence of symptoms of common mental disorders (CMD; distress, anxiety/depression, sleep disturbance, eating disorders, adverse alcohol use) among European professional football referees. A secondary aim was to explore the view of European professional football referees on consequences, support and needs related to these symptoms.An observational prospective cohort study with three measurements over a follow-up period of one season (2015-2016) was conducted among central or assistant professional football referees from Belgium, Finland, France, Germany, Norway, Russia, Scotland and Sweden. Using validated questionnaires to assess symptoms of CMD (self-reported and not clinically diagnosed), an electronic questionnaire in English and French was set up and distributed by the eight football federations involved. A total of 391 referees (mean age of 33 years old; mean career duration of 7 years) were enrolled, of which 292 completed the follow-up period. Baseline 4-week prevalence rates were 6% for distress, 12% for anxiety/depression, 9% for sleep disturbance, 19% for eating disorders and 17% for adverse alcohol use. The one-season incidence of symptoms of CMD was 10% for distress, 16% for anxiety/depression, 14% for sleep disturbance, 29% for eating disorders and 8% for adverse alcohol use. While symptoms of CMD occur among professional football referees and can influence negatively refereeing performances, the development of specific support measures for referees are needed in order to manage properly these symptoms of CMD.

#6 Effect of Instructions Prioritizing Speed or Accuracy on Kinematics and Kicking Performance in Football Players
Reference: J Mot Behav. 2016 Oct 14:1-8. [Epub ahead of print]
Authors: van den Tillaar R, Fuglstad P
Summary: The authors' purpose was to investigate if there is a speed accuracy trade-off in soccer kicking by using instructions prioritizing velocity, accuracy, or both upon soccer kicking performance and kicking direction in experienced soccer players. In addition, kinematics were measured to investigate the eventual differences in performance. Thirteen experienced male footballers performed penalty kicks with different instructions prioritizing velocity, accuracy or both. Three-dimensional kinematics, together with maximal ball velocity and hitting accuracy, were measured on all kicks. The main findings were that when the main aim was accuracy, accuracy increased, while the velocity reduced, which supports Fitts' law (Fitts, 1954 ). In addition, kicking accuracy was higher when kicking to the contralateral side. The slower ball velocity was caused by lower segmental and in run velocities. These lower segmental velocities were mainly caused by the lower maximal knee extension and pelvis rotation during the accuracy priority kicks.


#7 Validation of the FASH (Functional Assessment Scale for Acute Hamstring Injuries) questionnaire for German-speaking football players
Reference: J Orthop Surg Res. 2016 Oct 24;11(1):130.
Authors: Lohrer H, Nauck T, Korakakis V, Malliaropoulos N
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Summary: The FASH (Functional Assessment Scale for Acute Hamstring Injuries) questionnaire has been recently developed as a disease-specific self-administered questionnaire for use in Greek, English, and German languages. Its psychometric qualities (validity and reliability) were tested only in Greek-speaking patients mainly representing track and field athletes. As hamstring injuries represent the most common football injury, we tested the validity and reliability of the FASH-G (G = German version) questionnaire in German-speaking footballers suffering from acute hamstring injuries. The FASH-G questionnaire was tested for reliability and validity, in 16 footballers with hamstring injuries (patients' group), 77 asymptomatic footballers (healthy group), and 19 field hockey players (at-risk group). Known-group validity was tested by comparing the total FASH-G scores of the injured and non-injured groups. Reliability of the FASH-G questionnaire was analysed in 18 asymptomatic footballers using the intra-class coefficient. Known-group validity was demonstrated by significant differences between injured and non-injured participants (p < 0.001). The FASH-G exhibited very good test-retest reliability (intra-class correlation coefficient = 0.982, p < 0.001). Internal consistency was excellent (α = 0.938). Compared with the results presented in the original publication, no statistical differences were found between healthy athletes (p = 0.257), but patients' groups and at-risk groups presented scoring differences (p = 0.040 and <0.001, respectively). The FASH-G is a valid and reliable instrument to assess and determine the severity of hamstring injuries in German footballers.

#8 Relationship Between Running Performance and Recovery-Stress State in Collegiate Soccer Players
Reference: J Strength Cond Res. 2016 Oct 17. [Epub ahead of print]
Authors: Coker NA, Ake KM, Griffin DL, Rossi SJ, McMillan JL, Wells AJ.
Summary: The purpose of this study was to evaluate the relationship between changes in running performance and the stress-recovery state in collegiate soccer players. Running performance was evaluated in seven Division I NCAA male soccer players (179.39±5.24 cm; 75.46±5.98 kg; 20.37±1.41 yrs.) via global positioning system over the course of 12 competitive games in a single season. The regular season was divided into four competitive blocks: B1 (n=3), B2 (n=3), B3 (n=3) and B4 (n=3). Total distance and distance covered while engaging in walking, jogging, low-speed running, high-speed running, sprinting, low-intensity running and high-intensity running were assessed during each block. The RESTQ 52 Sport was administered twice during each block to evaluate measures of stress and recovery. Total distance was greater during B4 compared to B1 (p=0.027). Jogging and low-speed running were greater during B4 compared to all other time points (p's ≤ 0.05). Low-intensity running distance was greater during B4 compared to B1 (p=0.034). Sport-specific recovery decreased significantly during B4 compared to B1 (p=0.035). Correlational analysis indicated that high-velocity running was associated with increased stress, while low-velocity running was associated with greater recovery. However, changes in sport specific recovery did not correlate with changes in running performance from B1 to B4. Results of this study indicate that running performance decreased across the season. Changes in running performance coincided with a decrease in sport specific recovery. Practitioners may benefit from including the RESTQ as part of an assessment battery to monitor the stress/recovery state of athletes.

#9 Influence of Rest Intervals Following Assisted Sprinting on Bodyweight Sprint Times in Female Collegiate Soccer Players
Reference: J Strength Cond Res. 2016 Oct 6. [Epub ahead of print]
Authors: Nealer AL, Dunnick DD, Malyszek KK, Wong MA, Costa PB, Coburn JW, Brown LE
Summary: Speed is a crucial element an athlete must possess to be successful. In soccer, the ability to accelerate faster than your opponent can result in being first to reach a ball on a breakaway or stopping a counter attack. A unique way to train explosive movements is to evoke postactivation potentiation (PAP) in the working muscles. Traditionally, an overload stimulus with a long rest period is used, but a model utilizing an overspeed stimulus with shorter rest periods is less understood. Therefore, the purpose of this study was to determine the acute effects of varied rest intervals following assisted sprinting on bodyweight sprint time. Twenty-four female soccer players were split into two groups: recreational (n:11; age:20±1.67yrs; ht:162.30±4.35cm; mass:61.02±8.78kg) and collegiate athletes (n:13; age:19.76±0.83yrs; ht:166.85±5.98cm; mass:61.23±3.77kg). All participants attended five separate sessions, performed a dynamic warm up, then executed one 20m sprint (with 5m splits) at 30% bodyweight assistance (BWA). They then rested for 30s, one, two, or 4min in random order, followed by one bodyweight sprint with no BWA. Baseline sprint times were measured without BWA on the initial session of testing. Results revealed no difference in sprint time for the full 20m distance in either group. However, sprint time was significantly decreased for the 0-5m split only for the athletes following 1min (1.15±0.06s) and 2min (1.16±0.06s) rest compared to baseline (1.21±0.04s). Therefore, trained athletes should rest one or two minutes after 30% BWA supramaximal sprinting for increased bodyweight sprint speed.

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