Latest research in football - week 18 - 2018

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 a lighter, smaller football on acute match injuries in adolescent female football: a pilot cluster-randomized controlled trial
Reference: J Sports Med Phys Fitness. 2018 May;58(5):644-650. doi: 10.23736/S0022-4707.17.07903-8.
Authors: Zebis MK, Thorborg K, Andersen LL, Moller M, Christensen KB, Clausen MB, Holmich P, Wedderkopp N, Andersen TB, Krustrup P
Summary: The high injury incidence during match-play in female adolescent football is a major concern. In football, males and females play matches with the same football size. No studies have investigated the effect of football size on injury incidence in female adolescent football. Thus, the aim of the present study was to investigate the effects of introducing a lighter, smaller football on the injury pattern in female adolescent football. We conducted a pilot cluster randomized controlled trial including 26 football teams representing 346 adolescent female football players (age 15-18 years). The teams were randomized to a new lighter, smaller football (INT, N.=12 teams) or a traditional FIFA size 5 football (CON, N.=14 teams) during a full match-season. Acute time-loss injuries and football-exposure during match-play were reported weekly by text-message questions and verified subsequently by telephone interview. In total, 46 acute time-loss injuries were registered (5 severe injuries), yielding an incidence rate of 15.2 injuries per 1000 hours of match-play (95% CI: 8.5-27.2) in INT and 18.6 injuries per 1000 hours of match-play (95% CI: 14.0-24.8) in CON. The estimated 22% greater injury incidence rate risk (IRR: 1.22 [95% CI: 0.64-2.35]) in the CON group was not significant. With an IRR of 1.22, a future RCT main study would need to observe 793 acute time-loss injuries during match-play, in order to have a power of 80%. A large-scaled RCT is required to definitively test for beneficial or harmful effects of a lighter, smaller football in adolescent female football.

#2 Football training improves metabolic and cardiovascular health status in 55- to 70-year-old women and men with prediabetes
Reference: Scand J Med Sci Sports. 2018 May 2. doi: 10.1111/sms.13081. [Epub ahead of print]
Authors: Skoradal MB, Weihe P, Patursson P, Mortensen J, Connolly L, Krustrup P, Mohr M
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Summary: We examined the effects of 16 weeks of football training and dietary advice on blood glucose control and health status in 55- to 70-year-old women and men with prediabetes. Fifty participants with prediabetes (age; 61 ± 6 years, BMI; 29.6 ± 4.7; VO2max 22.3 ± 5.7 mL·min-1 ·kg-1 ) were randomized into a football and dietary advice group (F+D; n = 27) and a dietary advice group (D; n = 23). F+D performed football training (twice weekly 30- to 60-minutes sessions) and received dietary advice, while D only received dietary advice. An oral glucose tolerance test (OGTT) was completed pre and post the 16-week period. Body composition, blood pressure, and maximal oxygen uptake (VO2max ) were additionally measured. Both groups demonstrated a decrement (P < .05) in fasting blood glucose (-0.4 ± 0.5 mmol·L-1 ) and lowered blood glucose throughout OGTT. F+D displayed lower values than D (P < .05) after 60 minutes (9.0 ± 2.7 vs 10.6 ± 2.9 mmol·L-1 ) and 120 minutes (5.7 ± 1.6 vs 7.5 ± 2.4 mmol·L-1 ). VO2max increased by 14% in F+D, with a higher (P < .05) change score than in D (2%). Mean arterial pressure declined more (P < .05) in F+D than in D (-8 ± 9 vs -4 ± 11 mm Hg). Fat loss was greater (P < .05) in F+D than in D (-3.4 ± 2.8 vs -1.2 ± 2.0 kg), and the increase in lean body mass was also greater (P < .05) in F+D than in D (0.7 ± 1.5 vs -0.3 ± 1.6 kg). In conclusion, football training combined with dietary advice has broad-spectrum effects on metabolic and cardiovascular health profile with greater overall effects than professional dietary advice per se for 55- to 70-year-old women and men with prediabetes.

#3 Longitudinal motor performance development in early adolescence and its relationship to adult success: An 8-year prospective study of highly talented soccer players
Reference: PLoS One. 2018 May 3;13(5):e0196324. doi: 10.1371/journal.pone.0196324. eCollection 2018.
Authors: Leyhr D, Kelava A, Raabe J, Honer O
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Summary: Several talent identification and development (TID) programs in soccer have implemented diagnostics to measure players' motor performance. Yet, there is a lack of research investigating the relationship between motor development in adolescence and future, adult performance. This longitudinal study analyzed the three-year development of highly talented young soccer players' speed abilities and technical skills and examined the relevance of this development to their adult success. The current research sample consisted of N = 1,134 players born between 1993 and 1995 who were selected for the German Soccer Association's TID program and participated in nationwide motor diagnostics (sprinting, agility, dribbling, ball control, shooting) four times between the Under 12 (U12) and Under 15 (U15) age class. Relative age (RA) was assessed for all players, and a total motor score was calculated based on performances in the individual tests. In order to investigate players' future success, participants were divided into two groups according to their adult performance level (APL) in the 2014/2015 season: Elite (1st-5th German division; N = 145, 12.8%) and non-elite players (lower divisions; N = 989, 87.2%). Using multilevel regression analyses each motor performance was predicted by Time, Time2 (level-1 predictors), APL, and RA (level-2 covariates) with simultaneous consideration for interaction effects between the respective variables. Time and Time2 were significant predictors for each test performance. A predictive value for RA was confirmed for sprinting and the total motor score. A significant relationship between APL and the motor score as well as between APL and agility, dribbling, ball control, and shooting emerged. Interaction effects distinctly failed to reach significance. The study found a non-linear improvement in players' performance for all considered motor performance factors over a three-year period from early to middle adolescence. While their predictive value for future success was confirmed by a significant relationship between APL and most of the considered factors, there was no significant interaction between APL and Time. These findings indicate that future elite players had already been better at the beginning of the TID program and maintained this high level throughout their promotion from U12 to U15.

#4 Heading Frequency Is More Strongly Related to Cognitive Performance Than Unintentional Head Impacts in Amateur Soccer Players
Reference: Front Neurol. 2018 Apr 24;9:240. doi: 10.3389/fneur.2018.00240. eCollection 2018.
Authors: Stewart WF, Kim N, Ifrah C, Sliwinski M, Zimmerman ME, Kim M, Lipton RB, Lipton ML
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Summary: Compared to heading, unintentional head impacts (e.g., elbow to head, head to head, head to goalpost) in soccer are more strongly related to risk of moderate to very severe Central Nervous System (CNS) symptoms. But, most head impacts associated with CNS symptoms that occur in soccer are mild and are more strongly related to heading. We tested for a differential relation of heading and unintentional head impacts with neuropsychological (NP) test performance. Active adult amateur soccer players were recruited in New York City and the surrounding areas for this repeated measures longitudinal study of individuals who were enrolled if they had 5+ years of soccer play and were active playing soccer 6+ months/year. All participants completed a baseline validated questionnaire ("HeadCount-2w"), reporting 2-week recall of soccer activity, heading and unintentional head impacts. In addition, participants also completed NP tests of verbal learning, verbal memory, psychomotor speed, attention, and working memory. Most participants also completed one or more identical follow-up protocols (i.e., HeadCount-2w and NP tests) at 3- to 6-month intervals over a 2-year period. Repeated measures General Estimating Equations (GEE) linear models were used to determine if variation in NP tests at each visit was related to variation in either heading or unintentional head impacts in the 2-week period before testing. 308 players (78% male) completed 741 HeadCount-2w. Mean (median) heading/2-weeks was 50 (17) for men and 26 (7) for women. Heading was significantly associated with poorer performance on psychomotor speed (p < 0.001) and attention (p = 0.02) tasks and was borderline significant with poorer performance on the working memory (p  = 0.06) task. Unintentional head impacts were not significantly associated with any NP test. Results did not differ after excluding 22 HeadCount-2w with reported concussive or borderline concussive symptoms. Poorer NP test performance was consistently related to frequent heading during soccer practice and competition in the 2 weeks before testing. In contrast, unintentional head impacts incurred during soccer were not related to cognitive performance.

#5 Soccer Injury Movement Screen (SIMS) Composite Score Is Not Associated With Injury Among Semi-Professional Soccer Players
Reference: J Orthop Sports Phys Ther. 2018 May 8:1-29. doi: 10.2519/jospt.2018.8037. [Epub ahead of print]
Authors: McCunn R, Funten KA, Whalan M, Sampson JA, Meyer T
Summary: The association between movement quality and injury is equivocal. No soccer-specific movement assessment has been prospectively investigated in relation to injury risk. The aim was to investigate the association between a soccer-specific movement quality assessment and injury risk among semi-professional soccer players. Semi-professional soccer players (n=306) from 12 clubs completed the Soccer Injury Movement Screen (SIMS) during the pre-season period. Individual training/match exposure and non-contact time loss injuries were recorded prospectively for the entirety of the 2016 season. Relative risks (RR) were calculated, and presented with 90% confidence intervals (CI), for the SIMS composite and individual sub-test scores from generalized linear models with Poisson distribution offset for exposure. When considering non-contact time loss lower extremity injuries (primary level of analysis), there was a most likely trivial association with the SIMS composite score. Similarly, SIMS composite score demonstrated most likely to likely trivial associations to all injury categories included in the secondary level of analysis (non-contact time loss hip/groin, thigh, knee and ankle injuries). When considering hamstring strains and ankle sprains specifically (tertiary level of analysis) the SIMS composite score, again, demonstrated very likely trivial associations. A total of 262 non-contact time loss injuries were recorded. The overall (training and match exposure combined) incidence of non-contact time loss injury was 12/1000 hours. The SIMS composite score demonstrated no association to any of the investigated categories of soccer-related injury. The SIMS composite score should not be used to group players into 'high' or 'low' risk groups.

#6 Accuracy of Anthropometric Equations for Estimating Body Fat in Professional Male Soccer Players Compared with DXA
Reference: J Sports Med (Hindawi Publ Corp). 2018 Mar 14;2018:6843792. doi: 10.1155/2018/6843792. eCollection 2018.
Authors: Lopez-Taylor JR1, Gonzalez-Mendoza RG1, Gaytan-Gonzalez A, Jimenez-Alvarado JA, Villegas-Balcazar M, Jauregui-Ulloa EE, Torres-Naranjo F
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Summary: There are several published anthropometric equations to estimate body fat percentage (BF%), and this may prompt uncertainty about their application. The purpose was to analyze the accuracy of several anthropometric equations (developed in athletic [AT] and nonathletic [NAT] populations) that estimate BF% comparing them with DXA. We evaluated 131 professional male soccer players (body mass: 73.2 ± 8.0 kg; height: 177.5 ± 5.8 cm; DXA BF% [median, 25th-75th percentile]: 14.0, 11.9-16.4%) aged 18 to 37 years. All subjects were evaluated with anthropometric measurements and a whole body DXA scan. BF% was estimated through 14 AT and 17 NAT anthropometric equations and compared with the measured DXA BF%. Mean differences and 95% limits of agreement were calculated for those anthropometric equations without significant differences with DXA. Five AT and seven NAT anthropometric equations did not differ significantly with DXA. From these, Oliver's and Civar's (AT) and Ball's and Wilmore's (NAT) equations showed the highest agreement with DXA. Their 95% limits of agreement ranged from -3.9 to 2.3%, -4.8 to 1.8%, -3.4 to 3.1%, and -3.9 to 3.0%, respectively.Oliver's, Ball's, Civar's, and Wilmore's equations were the best to estimate BF% accurately compared with DXA in professional male soccer players.

#7 Planning Training Workload in Football Using Small-Sided Games' Density
Reference: J Strength Cond Res. 2018 May 8. doi: 10.1519/JSC.0000000000002598. [Epub ahead of print]
Authors: Sangnier S, Cotte T, Brachet O, Coquart J, Tourny C
Summary: To develop the physical qualities, the small-sided games' (SSGs) density may be essential in soccer. Small-sided games are games in which the pitch size, players' number, and rules are different to those for traditional soccer matches. The purpose was to assess the relation between training workload and SSGs' density. The 33 densities data (41 practice games and 3 full games) were analyzed through global positioning system (GPS) data collected from 25 professional soccer players (80.7 ± 7.0 kg; 1.83 ± 0.05 m; 26.4 ± 4.9 years). From total distance, distance metabolic power, sprint distance, and acceleration distance, the data GPS were divided into 4 categories: endurance, power, speed, and strength. Statistical analysis compared the relation between GPS values and SSGs' densities, and 3 methods were applied to assess models (R-squared, root-mean-square error, and Akaike information criterion). The results suggest that all the GPS data match the player's essential athletic skills. They were all correlated with the game's density. Acceleration distance, deceleration distance, metabolic power, and total distance followed a logarithmic regression model, whereas distance and number of sprints follow a linear regression model. The research reveals options to monitor the training workload. Coaches could anticipate the load resulting from the SSGs and adjust the field size to the players' number. Taking into account the field size during SSGs enables coaches to target the most favorable density for developing expected physical qualities. Calibrating intensity during SSGs would allow coaches to assess each athletic skill in the same conditions of intensity as in the competition.

#8 Physical performance tests - a relationship of risk factors for muscle injuries in elite level male football players
Reference: J Exerc Rehabil. 2018 Apr 26;14(2):282-288. doi: 10.12965/jer.1836028.014. eCollection 2018 Apr.
Authors: Svensson K, Alricsson M, Olausson M, Werner S
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Summary: The purpose of the present study was to investigate whether there is a relationship between the outcome of preseason physical performance tests and the risk of sustaining lower extremity muscle injuries within the same season, in male football players at elite level. This is a cohort study of a male football team (63 players) from the first league in Sweden. The football players are prospectively followed, in terms of muscle injuries of the lower extremity during five seasons between 2010 and 2014. All muscle injuries were evaluated and diagnosed with ultraso-nography. The following physical performance tests were included: squats, chin-ups, YoYo intermittent recovery level 2, counter movement jump, squat jump, standing long jump, sprint, one leg squat test, and a functional movement screen. A total of 86 muscle injuries occurred during the study period. No significant correlation was found between the results of the physical performance tests and muscle injuries of the lower extremity. None of the evaluated tests predicted the risk of sus-taining muscle injuries of the lower extremity. We conclude that muscle injury risk factors are more complex than solely related to the results of the preseason physical performance tests.

#9 Perceived motivational factors for female football players during rehabilitation after sports injury - a qualitative interview study
Reference: J Exerc Rehabil. 2018 Apr 26;14(2):199-206. doi: 10.12965/jer.1836030.015. eCollection 2018 Apr.
Authors: Hildingsson M, Fitzgerald UT, Alricsson M
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Summary: Compliance with a rehabilitation program is significant among athletes following a sports injury. It is also one of the main factors that influence the rehabilitation process; moreover, the outcome is also influenced by the athlete's motivation. It is primarily an autonomous motivation, resulting in rehabilitation adherence. The aim of this study was to investigate the perceived motivation of female football players during rehabilitation after a sports injury and the extent to which these motivating factors were autonomous. Qualitative interviews, based on a semistructured interview guide with injured female football players undergoing rehabilitation, were analyzed using content analysis. The motivational factors that were described were their set goals, social support as well as external and internal pressures during rehabilitation. The perceived autonomy varied somewhat but overall, they experienced external motivation; therefore, the behavior was not entirely self-determined. Results are expected to provide a better understanding of women football players' motivation in relation to their rehabilitation; hence, physiotherapists and coaches who are part of the rehabilitation process can contribute by increasing the autonomous motivation, thus, improving the compliance and outcome of the rehabilitation.

#10 Sub-Elite Football Players With Hip-Related Groin Pain and Positive Flexion Adduction Internal Rotation Test Exhibit Distinct Biomechanical Differences Compared With the Asymptomatic Side
Reference: J Orthop Sports Phys Ther. 2018 May 8:1-26. doi: 10.2519/jospt.2018.7910. [Epub ahead of print]
Authors: King MG, Semciw AI, Hart HF, Schache AG, Middleton KJ, Heerey JJ, Agricola R, Crossley KM
Summary: Study Design Observational cross-sectional study. Background Hip-related groin pain is common in sub-elite football players and may be associated with altered hip biomechanics. Objectives To compare the hip biomechanics, bony hip morphology associated with femoroacetabular impingement (FAI) syndrome, and hip strength and range of motion between the symptomatic and asymptomatic limb of sub-elite football players with unilateral hip-related groin pain and a positive flexion adduction internal rotation test. Methods Fifteen sub-elite football (soccer) players with unilateral hip-related groin pain and a positive flexion adduction internal rotation test were recruited. Three-dimensional motion analysis and ground reaction force data were recorded for walking and a single leg drop jump (SLDJ) task. Participants also underwent a standard anterior-posterior hip radiograph and hip strength and range of movement assessment. Between-limb differences were assessed using paired t-tests or Wilcoxon sign-rank tests. Results The symptomatic limb displayed a smaller peak hip extension angle (P=.01) and a lower peak hip adduction moment (P=.03) compared with the asymptomatic limb during the stance phase of walking. Additionally, during the SLDJ, the symptomatic limb demonstrated less total sagittal plane range of motion (P=.04). The symptomatic limb also demonstrated less external rotation range of motion (P=.03) however, no differences were found between limbs for bony hip morphology associated with FAI syndrome or hip strength. Conclusion This study found between limb asymmetries in low- and high-impact functional tasks such as walking and a SLDJ in football players with unilateral hip-related groin pain. Despite unilateral pain, bony morphology associated with FAI syndrome did not differ between limbs

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