Latest research in football - week 48 - 2017

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 Movement pattern and physiological response in recreational small-sided football - effect of number of players with a fixed pitch size
Reference: J Sports Sci. 2017 Nov 13:1-8. doi: 10.1080/02640414.2017.1402552. [Epub ahead of print]
Authors: Randers MB, Orntoft C, Hagman M, Nielsen JJ, Krustrup P
Summary: Recreational soccer is an effective health-promoting activity, but it is unclear how different game formats influence internal and external load. Thus, to be able to advise how to maximise the outcome of recreational football, we examined movement pattern and physiological response in 11 untrained men (32.6 ± 6.7 yrs, 23.3 ± 4.9 fat%, 43.4 ± 5.3 ml·min-1·kg-1) during three football sessions comprising 4 × 12 min of 3v3, 5v5 or 7v7 with a constant pitch size of 20 × 40 m. Movement pattern, heart rate (HR), blood lactate and RPE were measured during and after the 12-min periods. Greater (P < 0.05) total distance and high-speed distance was covered during 3v3 than 5v5 (14 and 30%) and 7v7 (15 and 75%). Mean HR was higher in 3v3 (85.7 ± 5.7%HRmax) and 5v5 (84.2 ± 5.1%HRmax) than in 7v7 (80.7 ± 4.6%HRmax, P < 0.05) and percentage time >90%HR was higher in 3v3 (43 ± 18%, P < 0.05) than in 5v5 (28 ± 21%) and 7v7 (18 ± 14%). Blood lactate was higher in 3v3 (7.4 ± 2.7 mmol·l-1) than in 7v7 (4.5 ± 2.2 mmol·l-1, P < 0.001) but not in 5v5 (6.1 ± 2.1 mmol·l-1, P = 0.061). RPE was higher in 3v3 (6.7 ± 2.3, P < 0.01) than in 5v5 (5.2 ± 2.2) and 7v7 (4.3 ± 2.3). In conclusion, higher external and internal load was found with fewer players, when the pitch size is fixed.

#2 Body fat percentage comparisons between four methods in young football players: are they comparable?
Reference: Nutr Hosp. 2017 Oct 24;34(5):1119-1124. doi: 10.20960/nh.760.
Authors: Lozano Berges G, Matute Llorente A, Gomez Bruton A, Gonzalez Aguero A, Vicente Rodriguez G, Casajus JA
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Summary: Dual X-ray absorptiometry (DXA), air displacement plethysmography (ADP), bioelectrical impedance analysis (BIA) and anthropometry are four body composition methods that have been frequently used for the assessment of body fat percentage (%BF) in athletes. However, the agreement between these methods has not been studied yet in adolescent football players. The aim of this study was to compare %BF calculated by DXA, ADP, BIA and anthropometry in 92 participants. Sixty-four males (13.4 ± 0.6 years of age) and 28 females (13.4 ± 0.6 years) participated in this study. %BF was measured with four methods: DXA, ADP, BIA, and anthropometry. ADP %BF was calculated by using Siri's equation. The equation proposed by Slaughter et al. was used to calculate %BF by anthropometry. Paired t-test was used to compare %BF means. The heteroscedasticity was calculated by Bland-Altman analyses. Both in males and females, DXA, ADP, BIA and Slaughter et al. equation demonstrated significant %BF differences when compared to each other (p < 0.05); 95% limits of agreements ranged from 5.13 to 15.09% points. Only BIA showed heteroscedasticity compared to the other methods in both genders (p < 0.05). Although DXA, ADP, BIA, and anthropometry have been used in the scientific literature in order to assess %BF in adolescent football players, these results demonstrate that these body composition methods are not interchangeable in this population.

#3 Adoption and use of an injury prevention exercise programme in female football: a qualitative study among coaches
Reference: Scand J Med Sci Sports. 2017 Nov 11. doi: 10.1111/sms.13012. [Epub ahead of print]
Authors: Lindblom H, Carlfjord S, Hagglund M
Summary: This study focuses on an injury prevention exercise programme (IPEP), Knee Control, which has been shown to reduce the incidence of acute knee injury in female adolescent football players. The aim was to explore the factors influencing coaches' adoption and use of Knee Control within female football in Sweden. This was a qualitative study involving interviews with 20 strategically selected coaches for female football teams, predominantly adolescent teams. The semi-structured interview guide was influenced by the Health Belief Model, and an ecological perspective was adopted during the interviews. Interviews were analysed with qualitative content analysis. The results illustrate the different influences that interact on adoption and use of Knee Control by coaches. The coaches described themselves as crucial for Knee Control adoption and use, but external facilitators and barriers such as resources for training, social support from other coaches, clubs and football associations and player buy-in were also described as important. Knee Control characteristics, such as how well the programme fit the team, also influenced use of Knee Control. Many coaches modified the programme to improve player buy-in and Knee Control fit. Such modifications may risk compromising the preventive effect but may increase feasibility, i.e. the ease of using Knee Control, and thereby long-term use. These findings may guide the design and delivery of future IPEPs, and improve use of Knee Control, for example by expanding the programme to fit different target groups and supporting coaches and players in the use of Knee Control.

#4 Measurement properties and feasibility of the Loughborough soccer passing test: A systematic review
Reference: J Sports Sci. 2017 Nov 24:1-13. doi: 10.1080/02640414.2017.1409611. [Epub ahead of print]
Authors: Wen D, Robertson S, Hu G, Song B, Chen H
Summary: The purpose of this paper was to systematically review the literature and examine the research methodological quality, measurement properties and feasibility of the Loughborough Soccer Passing Test (LSPT). Databases were searched up to June 2017. Twenty five studies fulfilled the eligibility criteria. The main methodological limitations of the studies were the small sample size and the lack of information on participants and eligibility criteria. Results showed that test-retest reliability of the LSPT was moderate to excellent. Good discriminative validity was found between playing levels and ages. The LSPT was positively correlated with sprint, dribbling, and agility test; however, a weak correlation was established with in-game performance. Test responsiveness (an ability to detect change over time) to some external interventions was observed in studies. Adjusted Cronbach's alpha (α = 0.67), smallest worthwhile change (SWC = 0.8-3.8) and minimal detectable change (MDC50 = 1.9-11.3) were calculated based on available data. The findings indicate that the LSPT has acceptable test-retest reliability and discriminative validity. However, it may not be a feasible and effective way to interpret the intra-individual change of skill performance in practice. Future work should be undertaken to establish additional measurement properties of the LSPT, and to improve its practical feasibility.

#5 Neural bases of ingroup altruistic motivation in soccer fans
Reference: Sci Rep. 2017 Nov 23;7(1):16122. doi: 10.1038/s41598-017-15385-7.
Authors: Bortolini T, Bado P, Hoefle S, Engel A, Zahn R, de Oliveira Souza R, Dreher JC, Moll J
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Summary: Humans have a strong need to belong to social groups and a natural inclination to benefit ingroup members. Although the psychological mechanisms behind human prosociality have extensively been studied, the specific neural systems bridging group belongingness and altruistic motivation remain to be identified. Here, we used soccer fandom as an ecological framing of group membership to investigate the neural mechanisms underlying ingroup altruistic behaviour in male fans using event-related functional magnetic resonance. We designed an effort measure based on handgrip strength to assess the motivation to earn money (i) for oneself, (ii) for anonymous ingroup fans, or (iii) for a neutral group of anonymous non-fans. While overlapping valuation signals in the medial orbitofrontal cortex (mOFC) were observed for the three conditions, the subgenual cingulate cortex (SCC) exhibited increased functional connectivity with the mOFC as well as stronger hemodynamic responses for ingroup versus outgroup decisions. These findings indicate a key role for the SCC, a region previously implicated in altruistic decisions and group affiliation, in dovetailing altruistic motivations with neural valuation systems in real-life ingroup behaviour.

#6 Novel mathematical model to estimate ball impact force in soccer
Reference: Sports Biomech. 2017 Nov 22:1-17. doi: 10.1080/14763141.2017.1364415. [Epub ahead of print]
Authors: Iga T, Nunome H, Sano S, Sato N, Ikegami Y
Summary: The purpose was to assess ball impact force during soccer kicking is important to quantify from both performance and chronic injury prevention perspectives. We aimed to verify the appropriateness of previous models used to estimate ball impact force and to propose an improved model to better capture the time history of ball impact force. A soccer ball was fired directly onto a force platform (10 kHz) at five realistic kicking ball velocities and ball behaviour was captured by a high-speed camera (5,000 Hz). The time history of ball impact force was estimated using three existing models and two new models. A new mathematical model that took into account a rapid change in ball surface area and heterogeneous ball deformation showed a distinctive advantage to estimate the peak forces and its occurrence times and to reproduce time history of ball impact forces more precisely, thereby reinforcing the possible mechanics of 'footballer's ankle'. Ball impact time was also systematically shortened when ball velocity increases in contrast to practical understanding for producing faster ball velocity, however, the aspect of ball contact time must be considered carefully from practical point of view.

#7 Somatotrope Pituitary Function in Professional Soccer Players
Reference: Exp Clin Endocrinol Diabetes. 2017 Nov 17. doi: 10.1055/s-0043-119876. [Epub ahead of print]
Authors: Roser P, Wehrhahn T, Krogmann H, Riedel N, Marshall RP, Gille J, Flitsch J, Aberle J
Summary: Soccer is associated with repetitive head trauma, which, as it is known from sports like football and boxing, can result in hypopituitarism. Gonadotropins and GH are the most common pituitary hormones to become deficient. GH deficiency is associated with an increased risk of cardiovascular mortality and has negative influence on body mass index, visceral fat mass, insulin resistance and sensitivity, bone mineral density and inflammatory markers. Therefore the aim of this study was to evaluate the somatotrope pituitary function in professional soccer players. This clinical study included 15 male, professional soccer players with at least 10 years of professional training. Basal hormonal parameters of the pituitary axis were obtained from the participants. To assess GH-IGF-I axis, glucagon stimulation tests were used. Rise in growth hormone during glucagon test was analyzed and the prevalence of newly diagnosed hormone deficiencies was evaluated. Mean age of all participants was 31±10 years. None of the 15 soccer players had GH deficiency. Mean rising factor of GH after stimulation with glucagon was 100 in all participants. We did not find signs of ACTH, TSH or LH/FSH deficiency in any player. In this small collective of soccer players we did not find playing soccer to be a risk factor for the development of GH-deficiency. According to our data screening for somatotrope deficiency is not necessary. Further investigations in larger cohorts are needed.

#8 Correction to: Tanner-Whitehouse Skeletal Ages in Male Youth Soccer Players: TW2 or TW3?
Reference: Sports Med. 2017 Nov 21. doi: 10.1007/s40279-017-0827-7. [Epub ahead of print]
Authors: Malina RM, Coelho-E-Silva MJ, Figueiredo AJ, Philippaerts RM, Hirose N, Reyes MEP, Gilli G, Benso A, Vaeyens R, Deprez D, Guglielmo LGA, Buranarugsa R
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Summary: An Online First version of this article was made available online at on 29 October 2017. Errors were subsequently identified in the article, and the following corrections should be noted.

#9 The functional movement screen (FMSTM) in elite young soccer players between 14 and 20 years: Composite score, individual test scores and asymmetries
Reference: Int J Sports Phys Ther. 2017 Nov;12(6):977-985.
Authors: Marques VB, Medeiros TM, de Souza Stigger F, Nakamura FY, Baroni BM
Summary: The Functional Movement Screen (FMS™) is a widely used seven-test battery used by practitioners working in sport medicine. The FMS™ composite score (sum of seven tests) in soccer athletes from different competitive levels has been well explored in literature, but the specific movement deficits presented by young high competitive level players remains unclear. The aim of the present study was to provide a detailed description of the performance of elite young soccer players (age 14-20 years) on the FMS™ testing battery. One-hundred and three young soccer players (14-20 years) from a premier league club were assessed by two experienced raters using the FMS™ testing battery. FMS™ composite score, individual-test scores and asymmetries were considered for analysis, and comparisons between age categories were performed. FMS™ composite scores ranged from 9 to 16 points (median=13 points). 82% of the athletes had a composite score ≤14 points, and 91% were classified into the "Fail" group (score 0 or 1 in at least one test). Almost half of athletes (48%) had poor performance (i.e., individual score < 2) in "deep squat" test. Most of athletes in the younger categories (under-15 and under-16) had poor performance in the "trunk stability push-up" test (70%) and in the "rotary stability" test (74%). Asymmetry in at least one of five unilateral FMS™ tests was found in 65% of athletes. High-performance young soccer players have important functional deficits, especially in tasks involving deep squat and trunk stability, as well as high prevalence of asymmetry between right and left body side.

#10 Vision in high-level football officials
Reference: PLoS One. 2017 Nov 21;12(11):e0188463. doi: 10.1371/journal.pone.0188463. eCollection 2017.
Authors: Baptista AMG, Serra PM, McAlinden C, Barrett BT
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Summary: Officiating in football depends, at least to some extent, upon adequate visual function. However, there is no vision standard for football officiating and the nature of the relationship between officiating performance and level of vision is unknown. As a first step in characterising this relationship, we report on the clinically-measured vision and on the perceived level of vision in elite-level, Portuguese football officials. Seventy-one referees (R) and assistant referees (AR) participated in the study, representing 92% of the total population of elite level football officials in Portugal in the 2013/2014 season. Nine of the 22 Rs (40.9%) and ten of the 49 ARs (20.4%) were international-level. Information about visual history was also gathered. Perceived vision was assessed using the preference-values-assigned-to-global-visual-status (PVVS) and the Quality-of-Vision (QoV) questionnaire. Standard clinical vision measures (including visual acuity, contrast sensitivity and stereopsis) were gathered in a subset (n = 44, 62%) of the participants. Data were analysed according to the type (R/AR) and level (international/national) of official, and Bonferroni corrections were applied to reduce the risk of type I errors. Adopting criterion for statistical significance of p<0.01, PVVS scores did not differ between R and AR (p = 0.88), or between national- and international-level officials (p = 0.66). Similarly, QoV scores did not differ between R and AR in frequency (p = 0.50), severity (p = 0.71) or bothersomeness (p = 0.81) of symptoms, or between international-level vs national-level officials for frequency (p = 0.03) or bothersomeness (p = 0.07) of symptoms. However, international-level officials reported less severe symptoms than their national-level counterparts (p<0.01). Overall, 18.3% of officials had either never had an eye examination or if they had, it was more than 3 years previously. Regarding refractive correction, 4.2% had undergone refractive surgery and 23.9% wear contact lenses when officiating. Clinical vision measures in the football officials were similar to published normative values for young, adult populations and similar between R and AR. Clinically-measured vision did not differ according to officiating level. Visual acuity measured with and without a pinhole disc indicated that around one quarter of participants may be capable of better vision when officiating, as evidenced by better acuity (≥1 line of letters) using the pinhole. Amongst the clinical visual tests we used, we did not find evidence for above-average performance in elite-level football officials. Although the impact of uncorrected mild to moderate refractive error upon officiating performance is unknown, with a greater uptake of eye examinations, visual acuity may be improved in around a quarter of officials.

#11 Monitoring the effect of football match congestion on hamstring strength and lower limb flexibility: Potential for secondary injury prevention?
Reference: Phys Ther Sport. 2017 Sep 15;29:14-18. doi: 10.1016/j.ptsp.2017.09.001. [Epub ahead of print]
Authors: Wollin M, Thorborg K, Pizzari T
Summary: The purpose was to investigate the effect of competitive football match congestion on hamstring strength and lower limb flexibility. Fifteen male elite youth football players from the national football association centre of excellence were included (age = 15.81 ±0.65 years, height = 171.95 ±6.89 cm, weight = 65.93 ±7.53 kg). Hamstring strength and pain, ankle dorsiflexion, hip extension, knee extension and flexion range of motion were used as main outcome measures. Hamstring strength was highest at baseline and significantly reduced at 24 (p = 0.001, mean difference -0.19 Nm/Kg, CI95 -0.28, -0.1) and 48 h post-match 1 (p = 0.002, mean difference -0.16 Nm/Kg, CI95 -0.25, -0.07). Strength recovered by match day 2 before significantly reducing again 24 h post-match 2 (p = 0.012, mean difference -0.17 Nm/Kg, CI95 -0.29, -0.04). Pain was lowest at baseline and increased in the post-match periods (p < 0.05) with standardised effect sizes ranging from 0.07 to 0.42. Passive knee flexion range decreased post-match (p < 0.01) with mean differences of 1.5°-2.7°. The other flexibility measures remained unaffected by match play. Isometric hamstring strength and pain can be considered for inclusion in-season to monitor player's post-match hamstring recovery characteristics during congested match fixtures.

#12 Alcohol intoxication at Swedish football matches: A study using biological sampling to assess blood alcohol concentration levels among spectators
Reference: PLoS One. 2017 Nov 20;12(11):e0188284. doi: 10.1371/journal.pone.0188284. eCollection 2017.
Authors: Durbeej N, Elgan TH, Jalling C, Gripenberg J
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Summary: Alcohol use and alcohol-related problems, including accidents, vandalism and violence, at sporting events are of increased concern in Sweden and other countries. The relationship between alcohol use and violence has been established and can be explained by the level of intoxication. Given the occurrence of alcohol use and alcohol-related problems at sporting events, research has assessed intoxication levels measured through biological sampling among spectators. This cross-sectional study aimed to assess the level of alcohol intoxication among spectators at football matches in the Swedish Premier Football League. Spectators were randomly selected and invited to participate in the study. Alcohol intoxication was measured with a breath analyser for Blood Alcohol Concentration levels, and data on gender, age, and recent alcohol use were gathered through a face-to-face interview. Blood Alcohol Concentration samples from 4420 spectators were collected. Almost half (46.8%) had a positive Blood Alcohol Concentration level, with a mean value of 0.063%, while 8.9% had a Blood Alcohol Concentration level ≥ 0.1%, with a mean value of 0.135%. Factors that predicted a higher Blood Alcohol Concentration level included male gender (p = 0.005), lower age (p < 0.001), attending a local derby (p < 0.001), alcohol use prior to having entered the arena (p < 0.001), attending a weekend match (p < 0.001), and being a spectator at supporter sections (p < 0.001). About half of all spectators at football matches in the Swedish Premier Football League drink alcohol in conjunction with the match. Approximately one tenth have a high level of alcohol intoxication.

#13 Longitudinal improvement in Balance Error Scoring System scores among NCAA Division-I football athletes
Reference: J Neurotrauma. 2017 Nov 17. doi: 10.1089/neu.2017.5072. [Epub ahead of print]
Authors: Mathiasen RE, Hogrefe CP, Harland KK, Peterson A, Smoot K
Summary: The Balance Error Scoring System (BESS) is a commonly used concussion assessment tool. Recent studies have questioned the stability and reliability of baseline BESS scores. The purpose of this longitudinal prospective cohort study is to examine differences in yearly baseline BESS scores in athletes participating on an NCAA Division-I football team. NCAA Division-I freshman football athletes were videotaped performing the BESS test at matriculation and following one year of participation in the football program. Twenty-three athletes were enrolled in year one of the study, and twenty-five athletes were enrolled in year two. Those athletes enrolled in year one were again videotaped following year two of the study. The paired t-test was used to assess for change in score over time for the firm surface, foam surface, and the cumulative BESS score. Additionally, inter- and intra-rater reliability values were calculated. Cumulative errors on the BESS significantly decreased from a mean of 20.3 at baseline to 16.8 after one year of participation. The mean number of errors following the second year of participation was 15.0. Inter-rater reliability for the cumulative score ranged from 0.65 to 0.75. Intra-rater reliability was 0.81. Following one year of participation, there is a statistically and clinically significant improvement in BESS scores in an NCAA Division-I football program. While additional improvement in the BESS scores was noted following the second year of participation, it did not reach statistical significance. Football athletes should undergo baseline BESS testing at least yearly if the BESS is to optimally useful as a diagnostic test for concussion.

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