Latest research in football - week 14 - 2015

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 Preventive Effect of the Nordic Hamstring Exercise on Hamstring Injuries in Amateur Soccer Players: A Randomized Controlled Trial
Reference: Am J Sports Med. 2015 Mar 20. pii: 0363546515574057. [Epub ahead of print]
Authors: van der Horst N, Smits DW, Petersen J, Goedhart EA, Backx FJ
Summary: Hamstring injuries are the most common muscle injuries in soccer, and they have a high rate of recurrence. Eccentric hamstrings strength is recognized as an important modifiable risk factor. This led to the development of prevention exercises such as the nordic hamstring exercise (NHE). The effectiveness of the NHE on hamstring injury prevention has never been investigated in amateur soccer. The purpose of the study was to investigate the preventive effect of the NHE on the incidence and severity of hamstring injuries in male amateur soccer players. Male amateur soccer players (age, mean ± SD, 24.5 ± 3.8 years) from 40 teams were randomly allocated to an intervention (n = 20 teams, 292 players) or control group (n = 20 teams, 287 players). The intervention group was instructed to perform 25 sessions of NHE in a 13-week period. Both the intervention and control groups performed regular soccer training and were followed for hamstring injury incidence and severity during the 2013 calendar year. At baseline, personal characteristics (eg, age, injury history, field position) were gathered from all participants via a questionnaire. Primary outcome was injury incidence. Secondary outcomes were injury severity and compliance with the intervention protocol. A total of 38 hamstring injuries were recorded, affecting 36 of 579 players (6.2%). The overall injury incidence rate was 0.7 (95% CI, 0.6-0.8) per 1000 player hours, 0.33 (95% CI, 0.25-0.46) in training, and 1.2 (95% CI, 0.82-1.94) in matches. Injury incidence rates were significantly different between the intervention (0.25; 95% CI, 0.19-0.35) and control groups (0.8; 95% CI, 0.61-1.15), χ2(1, n = 579) = 7.865; P = .005. The risk for hamstring injuries was reduced in the intervention group compared with the control group (odds ratio, 0.282; 95% CI, 0.110-0.721) and was statistically significant (P = .005). No statistically significant differences were identified between the intervention and control groups regarding injury severity. Compliance with the intervention protocol was 91%. Incorporating the NHE protocol in regular amateur training significantly reduces hamstring injury incidence, but it does not reduce hamstring injury severity. Compliance with the intervention was excellent.

#2 Football as Risk Factor for a Non-Injury-Related Knee Osteoarthritis - Results from a Systematic Review and Meta-analysis
Reference: Sportverletz Sportschaden. 2015 Mar;29(1):27-39. doi: 10.1055/s-0034-1385731. Epub 2015 Mar 23. [Article in German]
Authors: Spahn G, Grosser V, Schiltenwolf M, Schröter F, Grifka J
Summary: This systematic review and the meta-analysis were performed to investigate the relation between football activity and the potential risk of knee osteoarthritis (possible occupational disease). It was hypothesised that soccer players suffer more than controls from knee osteoarthritis also in cases with an absence of documented major injuries. The review and the metaanalysis were performed accordingly to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. On 2014.02.01 a search was conducted within the medical databases PubMed, Medline, Cochrane, EMBASE und Web-of-Science. A total of 4,649 papers underwent a "Title-Abstract-Review". Finally 6 publications were included in the metaanaylsis. There were no longitudinal community-based studies as well as no Cochrane Reviews regarding the risk of knee osteoarthritis in soccer players. After adjustment of major injuries of the knee, soccer players have a slightly increased risk for knee osteoarthritis: relative risk 1.3 (95 % CI 1.0 - 1.7); I(2) = 37.4 %; p = 0.002. In contrast, in studies without differentiation of injured and non-injured knees, the relative risk was significantly increased: 2.9 (95 % CI 2.0 - 4.1); I(2) = 56.3 %; p < 0.001. Soccer players are a very heterogeneous group. The soccer player's knee undergoes different loadings including minor and major injuries. But the individual load also strongly depends on the player's status, his position within the football field and many other factors. In the absence of a major trauma the soccer player has only a slightly increased risk for the development of osteoarthritis. Thus we conclude that an injury in professional football does not fulfil the characteristics of an occupational disease.

#3 Team activity recognition in Association Football using a Bag-of-Words-based method
Reference: Hum Mov Sci. 2015 Mar 25;41:165-178. doi: 10.1016/j.humov.2015.03.007. [Epub ahead of print]
Authors: Montoliu R, Martín-Félez R, Torres-Sospedra J, Martínez-Usó A
Summary: In this paper, a new methodology is used to perform team activity recognition and analysis in Association Football. It is based on pattern recognition and machine learning techniques. In particular, a strategy based on the Bag-of-Words (BoW) technique is used to characterize short Football video clips that are used to explain the team's performance and to train advanced classifiers in automatic recognition of team activities. In addition to the neural network-based classifier, three more classifier families are tested: the k-Nearest Neighbor, the Support Vector Machine and the Random Forest. The results obtained show that the proposed methodology is able to explain the most common movements of a team and to perform the team activity recognition task with high accuracy when classifying three Football actions: Ball Possession, Quick Attack and Set Piece. Random Forest is the classifier obtaining the best classification results.

#4 The epidemiology of groin injury in senior football: a systematic review of prospective studies
Reference: Br J Sports Med. 2015 Apr 1. pii: bjsports-2015-094705. doi: 10.1136/bjsports-2015-094705. [Epub ahead of print]
Authors: Waldén M, Hägglund M, Ekstrand J
Summary: Groin injuries are troublesome in men's and women's football. The purpose was to review the literature on the epidemiology of groin injury in senior football and compare injury occurrence between sexes. Studies were identified through a search of PubMed, EMBASE, CINAHL and Web of Science, in the reference lists of the selected articles and the authors' bibliographies. The number of injuries, percentage of groin injury from all injuries and rate of groin injury per 1000 h were extracted. Exposure and injury data were aggregated across included studies and the absolute differences in groin injury proportion and rate of groin injury were compared between sexes. Risk of bias was assessed using a 5-item checklist. 34 articles met the study criteria and were included. The proportion of groin injury in club-seasonal football was 4-19% in men and 2-14% in women. Aggregated data analysis (29 studies) showed a higher relative proportion of groin injury in men than in women (12.8% vs 6.9%, absolute difference 5.9%, 95% CI 4.6% to 7.1%). The rate of groin injury varied from 0.2 to 2.1/1000 h in men and 0.1 to 0.6/1000 h in women's club football, and aggregated analysis (23 studies) showed a more than two-fold higher rate in men (0.83/1000 h vs 0.35/1000 h, rate ratio 2.4, 95% CI 2.0 to 2.9). High risk of bias was identified for participant selection (18 studies), exposure (17 studies) and precision estimate (16 studies). Groin injuries are frequent in senior football and are more common in men than women. Future research needs to be of higher quality.

#5 Football practice and urinary incontinence: Relation between morphology, function and biomechanics
Reference: J Biomech. 2015 Mar 19. pii: S0021-9290(15)00182-7. doi: 10.1016/j.jbiomech.2015.03.013. [Epub ahead of print]
Authors: Roza TD, Brandão S, Oliveira D, Mascarenhas T, Parente M, Duarte JA, Jorge RN
Summary: Current evidence points to a high prevalence of urinary incontinence among female athletes. In this context, this study aims to assess if structural and biomechanical characteristics of the pubovisceral muscles may lead to urine leakage. Clinical and demographic data were collected, as well as pelvic Magnetic Resonance Imaging. Furthermore, computational models were built to verify if they were able to reproduce similar biomechanical muscle response as the one measured by dynamic imaging during active contraction by means of the percent error. Compared to the continent ones (n=7), incontinent athletes (n=5) evidenced thicker pubovisceral muscles at the level of the midvagina (p=0.019 and p=0.028 for the right and left sides, respectively). However, there were no differences neither in the strength of contraction in the Oxford Scale or in the displacement of the pelvic floor muscles during simulation of voluntary contraction, which suggests that urine leakage may be related with alterations in the intrafusal fibers than just the result of thicker muscles. Additionally, we found similar values of displacement retrieved from dynamic images and numerical models (6.42±0.36mm vs. 6.10±0.47mm; p=0.130), with a percent error ranging from 1.47% to 17.20%. However, further refinements in the mechanical properties of the striated skeletal fibers of the pelvic floor muscles and the inclusion of pelvic organs, fascia and ligaments would reproduce more realistically the pelvic cavity.

#6 Effectiveness Analysis of Active Stretching Versus Active Stretching Plus Low-Frequency Electrical Stimulation in Children Who Play Soccer and Who Have the Short Hamstring Syndrome
Reference: Clin J Sport Med. 2015 Mar 18. [Epub ahead of print]
Authors: Piqueras-Rodríguez F, Palazón-Bru A, Gil-Guillén VF
Summary: The purpose was to determine the effectiveness of active stretching (AS) versus AS plus electrical stimulation (stretching + TENS) in young soccer players with the short hamstring syndrome (SHS). The study involved young federated soccer players in the town of Jumilla, in the region of Murcia (Spain), who were controlled in a physiotherapy office in 2012. Fifty-one young soccer players (10-16 years) with SHS were part of the study. Main outcome measures were the straight leg raise (SLR) test, popliteal angle with the passive knee extension (PKE) test, and the toe-touch test (TT). Significant results (P < 0.05) were group 1 versus 2: (1) SLR, -5.5 degrees right; (2) PKE, +10.2 degrees right and +6.2 degrees left; and (3) range of values of clinically relevant parameters (RVCRP): relative risk (RR), 0.35 to 0.38; relative risk reduction (RRR), 0.62 to 0.65; absolute risk reduction (ARR), 0.32 to 0.39; number needed to treat (NNT), 3 to 4. Group 1 versus 3: (1) SLR, -12.3 degrees right and -10 degrees left; (2) PKE, +12.9 degrees right and +8.5 degrees left; (3) TT, -8.9 cm; and (4) RVCRP: RR, 0.12 to 0.28; RRR, 0.72 to 0.88; ARR, 0.60 to 0.83; NNT, 2 to 2. Group 2 versus 3: (1) SLR, -6.8 degrees right and -6.2 degrees left; (2) TT, -6.7 cm; (3) RVCRP: RR, 0.44 to 0.53; RRR, 0.47 to 0.56; ARR, 0.40 to 0.56; NNT, 2 to 3. Stretching + TENS produces greater improvement than AS alone, and these are both better than conventional stretching.

#7 Altered Neurochemistry in Former Professional Soccer Players without a History of Concussion
Reference: J Neurotrauma. 2015 Apr 4. [Epub ahead of print]
Authors: Koerte IK, Lin AP, Muehlmann M, Merugumala S, Liao H, Starr T, Kaufmann D, Mayinger M, Steffinger D, Fisch B, Karch S, Heinen F, Ertl-Wagner B, Reiser M, Stern R, Zafonte RD, Shenton ME.
Summary: Soccer is played by more than 250 million people worldwide. Repeatedly heading the ball may place soccer players at high risk for repetitive subconcussive head impacts (RSHI). This study evaluates the long-term effects of RSHI on neurochemistry in athletes without a history of clinically diagnosed concussion, but with a high exposure to RSHI. Eleven former professional soccer players (mean age 52.0 ± 6.8 years) and a comparison cohort of fourteen age- and gender-matched former non-contact sport athletes (mean age 46.9 ± 7.9 years) underwent 3T magnetic resonance spectroscopy (MRS) and neurocognitive evaluation. In the soccer players a significant increase was observed in both, choline, a membrane marker, and myo-inositol, a marker of glial activation, compared to control athletes. Additionally, myo-inositol and glutathione were significantly correlated with lifetime estimate of RSHI within the soccer group. There was no significant difference in neurocognitive tests between groups. Results of this study suggest an association between RSHI in soccer players and MRS markers of neuroinflammation, suggesting that even subconcussive head impacts affect the neurochemistry of the brain and may precede neurocognitive changes. Future studies will need to determine the role of neuroinflammation in RSHI and the effect on neurocognitive function.

#8 Football fan aggression: the importance of low Basal cortisol and a fair referee
Reference: PLoS One. 2015 Apr 6;10(4):e0120103. doi: 10.1371/journal.pone.0120103. eCollection 2015.
Authors: van der Meij L, Klauke F, Moore HL, Ludwig YS, Almela M, van Lange PA
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Summary: Fan aggression in football (soccer) is a societal problem that affects many countries worldwide. However, to date, most studies use an epidemiological or survey approach to explain football fan aggression. This study used a controlled laboratory study to advance a model of predictors for fan aggression. To do so, football fans (n = 74) saw a match summary in which their favorite team lost against their most important rival. Next, we measured levels of aggression with the hot sauce paradigm, in which fans were given the opportunity to administer a sample of hot sauce that a rival football supporter had to consume. To investigate if media exposure had the ability to reduce aggression, before the match fans saw a video in which fans of the rival team commented in a neutral, negative, or positive manner on their favorite team. Results showed that the media exposure did not affect aggression. However, participants displayed high levels of aggression and anger after having watched the match. Also, aggression was higher in fans with lower basal cortisol levels, which suggests that part of the aggression displayed was proactive and related to anti-social behavior. Furthermore, aggression was higher when the referee was blamed and aggression was lower when the performance of the participants' favorite team was blamed for the match result. These results indicate that aggression increased when the match result was perceived as unfair. Interventions that aim to reduce football fan aggression should give special attention to the perceived fairness of the match result.

#9 Reliability and sensitivity of a simple isometric posterior lower limb muscle test in professional football players
Reference: J Sports Sci. 2015 Apr 7:1-7. [Epub ahead of print]
Authors: McCall A, Nedelec M, Carling C, Le Gall F, Berthoin S, Dupont G
Summary: This study aimed (1) to determine the reliability of a simple and quick test to assess isometric posterior lower limb muscle force in professional football players and (2) verify its sensitivity to detect reductions in force following a competitive match. Twenty-nine professional football players performed a 3-s maximal isometric contraction of the posterior lower limb muscles for both legs with players lying supine. Both legs were tested using a knee angle of 90° and 30° measured on a force plate. Players were tested twice with one week between sessions to verify reliability. Sensitivity was tested following a full competitive football match. The test showed high reliability for dominant leg at 90° (CV = 4.3%, ICC = 0.95, ES = 0.15), non-dominant leg at 90° (CV = 5.4%, ICC = 0.95, ES = 0.14), and non-dominant leg at 30° (CV = 4.8%, ICC = 0.93, ES = 0.30) and good reliability for dominant leg at 30° (CV = 6.3%, ICC = 0.86, ES = 0.05). The measure was sensitive enough to detect reductions in force for dominant leg at 90° (P = 0.0006, ES > 1), non-dominant leg at 90° (P = 0.0142, ES = 1), and non-dominant leg at 30° (P = 0.0064, ES > 1) and for dominant leg at 30° (P = 0.0016, ES > 1). In conclusion, the present test represents a useful and practical field tool to determine the magnitude of match-induced fatigue of the posterior lower limb muscles and potentially to track their recovery.

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