Latest research in football - week 51 - 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 Nine-year study of US high school soccer injuries: data from a national sports injury surveillance programme
Reference: Br J Sports Med. 2016 Dec 28. pii: bjsports-2015-095946. doi: 10.1136/bjsports-2015-095946. [Epub ahead of print]
Authors: Khodaee M, Currie DW, Asif IM, Comstock RD
Summary: Research on high school soccer injury epidemiology is sparse. Therefore the purpose was to describe high school soccer injury rates, trends and patterns by type of athlete exposure (AE), position and sex. This descriptive epidemiological study used data from a large national high school sports injury surveillance programme to describe rates and patterns of soccer-related injuries including concussion sustained from 2005/2006 to 2013/2014. Injury rates are calculated per 1000 AEs. Overall, 6154 soccer injuries occurred during 2 985 991 AEs; injury rate=2.06 per 1000 AEs. Injury rates were higher during competition (4.42) than practice (1.05; rate ratio (RR)=4.19; 95% CI 3.98 to 4.41), and in girls (2.33) than boys (1.83; RR=1.27, 95% CI 1.21 to 1.34). Boys' non-concussion injury rates decreased significantly (p=0.001) during the study period while reported concussion rates increased significantly (p=0.002). Girls' non-concussion rates were relatively stable and reported concussion rates increased significantly (p=0.004). Player-player contact was the injury mechanism that led to the most competition injuries (injury proportion ratio (IPR)=2.87; 95% CI 2.57 to 3.21), while non-contact injuries were the most common mechanisms among practice injuries (IPR=2.10; 95% CI 1.86 to 2.38). Recovery from concussion was >7 days in a third of the cases. Injury patterns were similar between sexes with respect to position played and location on the field at the time of injury. High school soccer injury rates vary by sex and type of exposure, while injury patterns are more similar across sexes. Reported concussion rates increased significantly over the study period in male and female athletes.

#2 Effectiveness of a stress management pilot program aimed at reducing the incidence of sports injuries in young football (soccer) players
Reference: Phys Ther Sport. 2016 Sep 6. pii: S1466-853X(16)30097-9. doi: 10.1016/j.ptsp.2016.09.003. [Epub ahead of print]
Authors: Olmedilla-Zafra A, Rubio VJ, Ortega E, García-Mas A
Summary: Several attempts to reduce the incidence of sport injuries using psychosocial interventions produced fruitful, although inconclusive results. This paper presents the effectiveness and implementation issues of a pilot 3-month stress-management and muscle relaxation program aimed at reducing sport injury incidence. The program was administered by a trained psychologist on a once-a-week, 1-h session basis. Seventy-four male soccer players from four National Youth league teams voluntarily participated. Teams were randomly assigned to either treatment/non-treatment group. Injury protocol, Self-monitoring cards, Athletes' satisfaction and commitment survey, Coaches' interview were used as data measures.  Group main effect and Time-Group interaction effect were both statistically significant, F(1,60) = 8.30, p = 0.005, η2p = 0.121, with the average number of injuries larger in the post-treatment phase of non-treatment group (p = 0.005, η2p = 0.077). There was a significant decrease in the average number of injuries for the intervention group before and after implementing the program (p < 0.001, η2p = 0.309). A controlled implementation of a psychosocial program was effective in reducing youth soccer sport injuries, with a high level of satisfaction and commitment from the athletes, as well as high acceptance from the coaches.

#3 Exercise Intensity During Power Wheelchair Soccer
Reference: Arch Phys Med Rehabil. 2016 Nov;97(11):1938-1944. doi: 10.1016/j.apmr.2016.05.012. Epub 2016 Jun 8.
Authors: Barfield JP, Newsome L, Malone LA
Summary: The purpose was to determine exercise intensity during power wheelchair soccer among a sample of persons with mobility impairments. Participants with severe mobility impairments (N=30) (mean ± SD, age: 29.40±15.51y, body mass index: 24.11±6.47kg/m2, power soccer experience: 7.91±3.93y, disability sport experience: 12.44±9.73y) were recruited from multiple power wheelchair soccer teams. Portable metabolic carts were used to collect oxygen consumption (V˙o2) data during resting and game play conditions. Average V˙o2 (expressed in metabolic equivalent tasks [METs]) during resting and game play conditions and rating of perceived exertion for game play. V˙o2 increased from 1.35±0.47 METs at rest to 1.81±0.65 METs during game play. This 34% increase in exercise intensity was significant (P<.01) and supported by a mean perceived exertion score of approximately 13 (somewhat hard). Although not able to sustain an intensity associated with reduced secondary disease risk (ie, 3 METs), the documented light-intensity exercise in the current study surpassed an intensity threshold associated with improved functional capacity and performance of daily living activities (ie, 1.5 METs).

#4 Real Time Quantification of Dangerousity in Football Using Spatiotemporal Tracking Data
Reference: PLoS One. 2016 Dec 30;11(12):e0168768. doi: 10.1371/journal.pone.0168768. eCollection 2016.
Authors: Link D, Lang S, Seidenschwarz P

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Summary: This study describes an approach to quantification of attacking performance in football. Our procedure determines a quantitative representation of the probability of a goal being scored for every point in time at which a player is in possession of the ball-we refer to this as dangerousity. The calculation is based on the spatial constellation of the player and the ball, and comprises four components: (1) Zone describes the danger of a goal being scored from the position of the player on the ball, (2) Control stands for the extent to which the player can implement his tactical intention on the basis of the ball dynamics, (3) Pressure represents the possibility that the defending team prevent the player from completing an action with the ball and (4) Density is the chance of being able to defend the ball after the action. Other metrics can be derived from dangerousity by means of which questions relating to analysis of the play can be answered. Action Value represents the extent to which the player can make a situation more dangerous through his possession of the ball. Performance quantifies the number and quality of the attacks by a team over a period of time, while Dominance describes the difference in performance between teams. The evaluation uses the correlation between probability of winning the match (derived from betting odds) and performance indicators, and indicates that among Goal difference (r = .55), difference in Shots on Goal (r = .58), difference in Passing Accuracy (r = .56), Tackling Rate (r = .24) Ball Possession (r = .71) and Dominance (r = .82), the latter makes the largest contribution to explaining the skill of teams. We use these metrics to analyse individual actions in a match, to describe passages of play, and to characterise the performance and efficiency of teams over the season. For future studies, they provide a criterion that does not depend on chance or results to investigate the influence of central events in a match, various playing systems or tactical group concepts on success.

#5 Content Validity and Psychometric Properties of the Nomination Scale for Identifying Football Talent (NSIFT): Application to Coaches, Parents and Players
Reference: Sports 2017, 5(1), 2; doi:10.3390/sports5010002
Authors: Prieto-Ayuso A, Pastor-Vicedo JC, Contreras-Jordan O
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Summary: The identification of football talent is a critical issue both for clubs and the families of players. However, despite its importance in a sporting, economic and social sense, there appears to be a lack of instruments that can reliably measure talent performance. The aim of this study was to design and validate the Nomination Scale for Identifying Football Talent (NSIFT), with the aim of optimising the processes for identifying said talent. The scale was first validated through expert judgment, and then statistically, by means of an exploratory factor analysis (EFA), confirmatory factor analysis (CFA), internal reliability and convergent validity. The results reveal the presence of three factors in the scale’s factor matrix, with these results being confirmed by the CFA. The scale revealed suitable internal reliability and homogeneity indices. Convergent validity showed that it is teammates who are best able to identify football talent, followed by coaches and parents. It can be concluded that the NSIFT is suitable for use in the football world. Future studies should seek to confirm these results in different contexts by means of further CFAs.

#6 Comparison of T2* relaxation times of articular cartilage of the knee in elite professional football players and age-and BMI-matched amateur athletes
Reference: Eur J Radiol. 2017 Jan;86:105-111. doi: 10.1016/j.ejrad.2016.10.028. Epub 2016 Oct 27.
Authors: Behzadi C, Welsch GH, Laqmani A, Henes FO, Kaul MG, Schoen G, Adam G, Regier M
Summary: Recent investigation has underlined the potential of quantitative MR imaging to be used as a complementary tool for the diagnosis of cartilage degeneration at an early state. The presented study analyses T2* relaxation times of articular cartilage of the knee in professional athletes and compares the results to age- and BMI (Body Mass Index)-matched healthy amateur athletes. 22 professional football players and 22 age- and BMI-matched individuals were underwent knee Magnetic Resonance Imaging (MRI) at 3T including qualitative and quantitative analysis. Qualitative analysis included e.g. meniscal tears, joint effusion and bone edema. For quantitative analysis T2* (22 ET: 4.6-53.6ms) measurements in 3D data acquisition were performed. Deep and superficial layers of 22 predefined cartilage segments were analysed. All data sets were postprocessed using a dedicated software tool. Statistical analysis included Student t-test, confidence intervals and a random effects model. In both groups, T2* relaxation times were significantly higher in the superficial compared to the deep layers (p<0.001). Professional athletes had significantly higher relaxation times in eight superficial and three deep cartilage layers in the predefined cartilage segments (p<0.05). Highly significant differences were found in the weight-bearing segments of the lateral superficial femoral condyle (p<0.001). Elevated T2* values in cartilage layers of professional football players compared to amateur athletes were noted. The effects seem to predominate in superficial cartilage layers.

#7 Short Duration Small Sided Football and to a Lesser Extent Whole Body Vibration Exercise Induce Acute Changes in Markers of Bone Turnover
Reference: Biomed Res Int. 2016;2016:3574258. doi: 10.1155/2016/3574258. Epub 2016 Nov 29.
Authors: Bowtell JL, Jackman SR, Scott S, Connolly LJ, Mohr M, Ermidis G, Julian R, Yousefian F, Helge EW, Jorgensen NR, Fulford J, Knapp KM, Krustrup P
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Summary: We aimed to study whether short-duration vibration exercise or football sessions of two different durations acutely changed plasma markers of bone turnover and muscle strain. Inactive premenopausal women (n = 56) were randomized to complete a single bout of short (FG15) or long duration (FG60) small sided football or low magnitude whole body vibration training (VIB). Procollagen type 1 amino-terminal propeptide (P1NP) was increased during exercise for FG15 (51.6 ± 23.0 to 56.5 ± 22.5 μg·L-1, mean ± SD, P < 0.05) and FG60 (42.6 ± 11.8 to 50.2 ± 12.8 μg·L-1, P < 0.05) but not for VIB (38.8 ± 15.1 to 36.6 ± 14.7 μg·L-1, P > 0.05). An increase in osteocalcin was observed 48 h after exercise (P < 0.05), which did not differ between exercise groups. C-terminal telopeptide of type 1 collagen was not affected by exercise. Blood lactate concentration increased during exercise for FG15 (0.6 ± 0.2 to 3.4 ± 1.2 mM) and FG60 (0.6 ± 0.2 to 3.3 ± 2.0 mM), but not for VIB (0.6 ± 0.2 to 0.8 ± 0.4 mM) (P < 0.05). Plasma creatine kinase increased by 55 ± 63% and 137 ± 119% 48 h after FG15 and FG60 (P < 0.05), but not after VIB (26 ± 54%, NS). In contrast to the minor elevation in osteocalcin in response to a single session of vibration exercise, both short and longer durations of small sided football acutely increased plasma P1NP, osteocalcin, and creatine kinase. This may contribute to favorable effects of chronic training on musculoskeletal health.

#8 Examining the relationships between challenge and threat cognitive appraisals and coaching behaviours in football coaches
Reference: J Sports Sci. 2016 Dec 26:1-7. doi: 10.1080/02640414.2016.1273538. [Epub ahead of print]
Authors: Dixon M, Turner MJ, Gillman J
Summary: Previous research demonstrates that sports coaching is a stressful activity. This article investigates coaches' challenge and threat cognitive appraisals of stressful situations and their impact on coaching behaviour, using Blascovich and Mendes' (2000) biopsychosocial model as a theoretical framework. A cross-sectional correlational design was utilised to examine the relationships between irrational beliefs (Shortened general attitude and belief scale), challenge and threat appraisals (Appraisal of life events scale), and coaching behaviours (Leadership scale for sports) of 105 professional football academy coaches. Findings reveal significant positive associations between challenge appraisals and social support, and between threat appraisals and autocratic behaviour, and a significant negative association between threat appraisals and positive feedback. Results also show that higher irrational beliefs are associated with greater threat, and lesser challenge cognitive appraisals. However, no associations were revealed between irrational beliefs and challenge cognitive appraisals. Additionally, findings demonstrate a positive relationship between age and training and instruction. Results suggest that practitioners should help coaches to appraise stressful situations as a challenge to promote positive coaching behaviours.

#9 Somatic, Endurance Performance and Heart Rate Variability Profiles of Professional Soccer Players Grouped According to Age
Reference: J Hum Kinet. 2016 Dec 15;54:65-74. doi: 10.1515/hukin-2016-0035. eCollection 2016.
Authors: Botek M, Krejcj J, McKune AJ, Klimesova
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Summary: This cross-sectional study compared somatic, endurance performance determinants and heart rate variability (HRV) profiles of professional soccer players divided into different age groups: GI (17-19.9 years; n = 23), GII (20-24.9 years; n = 45), GIII (25-29.9 years; n = 30), and GIV (30-39 years; n = 26). Players underwent somatic and HRV assessment and maximal exercise testing. HRV was analyzed by spectral analysis of HRV, and high (HF) and low (LF) frequency power was transformed by a natural logarithm (Ln). Players in GIV (83 ± 7 kg) were heavier (p < 0.05) compared to both GI (73 ± 6 kg), and GII (78 ± 6 kg). Significantly lower maximal oxygen uptake (VO2max, ml•kg-1•min-1) was observed for GIV (56.6 ± 3.8) compared to GI (59.6 ± 3.9), GII (59.4 ± 4.2) and GIV (59.7 ± 4.1). All agegroups, except for GII, demonstrated comparable relative maximal power output (Pmax). For supine HRV, significantly lower Ln HF (ms2) was identified in both GIII (7.1 ± 0.8) and GIV (6.9 ± 1.0) compared to GI (7.9 ± 0.6) and GII (7.7 ± 0.9). In conclusion, soccer players aged >25 years showed negligible differences in Pmax unlike the age group differences demonstrated in VO2max. A shift towards relative sympathetic dominance, particularly due to reduced vagal activity, was apparent after approximately 8 years of competing at the professional level.

#10 Developing Talented Soccer Players: An Analysis of Socio-Spatial Factors as Possible Key Constraints
Reference: J Hum Kinet. 2016 Dec 15;54:227-236. doi: 10.1515/hukin-2016-0050. eCollection 2016.
Authors: Serra-Olivares J, Pastor-Vicedo JC, Gonzalez-Víllora S, Teoldo da Costa I
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Summary: Most studies on the identification and development of soccer talent have been one-dimensional in nature. Although some multi-dimensional analyses have been conducted, few research studies have assessed in any depth the socio-spatial factors influencing talent development. The aim of this particular study was to analyse variations in the international representation of clubs (n = 821) and countries (n = 59) in the development of players who took part in the 2014 FIFA Soccer World Cup. Clubs and countries were ranked and divided into quartiles according to the number of players developed between the ages of 15 and 21 (clubs and countries that developed players for at least three years between these ages) and the number of official league matches played by these players up to the age of 23. Significant variations were observed between clubs in terms of the number of developed players who took part in the World Cup and the number of official league matches played by these players up to the age of 23 (p < .05), and also between countries (p < .05). The findings reveal the need to carry out more in-depth studies into the type of training and competition engaged in by elite players in the period of development between the ages of 15 and 21. It may be the case that these factors are potentially decisive socio-spatial constraints in the development of soccer talent.

#11 Soccer Players Cultural Capital and Its Impact on Migration
Reference: J Hum Kinet. 2016 Dec 15;54:195-206. doi: 10.1515/hukin-2016-0052. eCollection 2016.
Authors: Krizaj J, Leskosek B, Vodicar J, Topic MD
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Summary: The purpose of this study was to identify factors that constituted the cultural capital among soccer players. We assumed that in the increasingly globalized world of professional soccer, a player's success would often depend on migrating and adjusting to life in other countries. Willingness to migrate and successful adjustment are tied to player's previous attitudes and/or behaviours (habitus), significant support from others, including family members, and previous experiences and success in sports and education. Our hypothesised model of the cultural capital was based on the Pierre Bourdieu's theoretical framework. It consisted of 26 variables related to three sets of factors: soccer experiences, a family context and support, and educational achievements of the players and their parents. The model was tested using a sample of 79 current soccer coaches who also had been players at the elite level. A factor analysis was used to empirically verify the content of the hypothetical model of the soccer players' cultural capital. Nine latent factors were extracted and together, they accounted for 55.01% of the total model variance. Individual factors obtained showed a sufficient level of substantial connection. The Cronbach's alpha value of 0.77 confirmed the internal consistency of the operationalised variables in the hypothetical model. In addition, the impact of these aforementioned life dimensions on the migration of soccer players was studied. The results of the binary logistic regression analysis showed that the first factor of the hypothetical model (F1) had 2.2 times and the second factor (F8) had 3.9 times higher odds for migration abroad. Sociocultural findings using this new assessment approach could help create better "success conditions" in the talent development of young players.

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