Latest research in football - week 1 - 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 Optimization of Game Formats in U-10 Soccer Using Logistic Regression Analysis
Reference: J Hum Kinet. 2016 Dec 15;54:163-171. doi: 10.1515/hukin-2016-0047. eCollection 2016.
Authors: Amatria M, Lapresa D, Arana J, Anguera MT, Garzon B
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Summary: Small-sided games provide young soccer players with better opportunities to develop their skills and progress as individual and team players. There is, however, little evidence on the effectiveness of different game formats in different age groups, and furthermore, these formats can vary between and even within countries. The Royal Spanish Soccer Association replaced the traditional grassroots 7-a-side format (F-7) with the 8-a-side format (F-8) in the 2011-12 season and the country's regional federations gradually followed suit. The aim of this observational methodology study was to investigate which of these formats best suited the learning needs of U-10 players transitioning from 5-aside futsal. We built a multiple logistic regression model to predict the success of offensive moves depending on the game format and the area of the pitch in which the move was initiated. Success was defined as a shot at the goal. We also built two simple logistic regression models to evaluate how the game format influenced the acquisition of technicaltactical skills. It was found that the probability of a shot at the goal was higher in F-7 than in F-8 for moves initiated in the Creation Sector-Own Half (0.08 vs 0.07) and the Creation Sector-Opponent's Half (0.18 vs 0.16). The probability was the same (0.04) in the Safety Sector. Children also had more opportunities to control the ball and pass or take a shot in the F-7 format (0.24 vs 0.20), and these were also more likely to be successful in this format (0.28 vs 0.19).

#2 Nonverbal Communication of Confidence in Soccer Referees: An Experimental Test of Darwin's Leakage Hypothesis
Reference: J Sport Exerc Psychol. 2016 Dec 29:1-24. doi: 10.1123/jsep.2016-0192. [Epub ahead of print]
Authors: Furley P, Schweizer G
Summary: The goal of the present paper was to investigate whether soccer referees' nonverbal behavior (NVB) differed based on the difficulty of their decisions and whether perceivers could detect these systematic variations. On the one hand, communicating confidence via NVB is emphasized in referee training. On the other hand, it seems feasible from a theoretical point of view that particularly following relatively difficult decisions referees have problems controlling their NVB. We conducted three experiments in order to investigate into this question. Experiment 1 (N = 40) and Experiment 2 (N = 60) provided evidence that perceivers regard referees' NVB as less confident following ambiguous decisions as compared to following unambigous decisions. Experiment 3 (N = 58) suggested that perceivers were more likely to debate with the referee when referees nonverbally communicated less confidence. We discuss consequences for referee training.

#3 Etiology and Recovery of Neuromuscular Fatigue following Simulated Soccer Match-Play
Reference: Med Sci Sports Exerc. 2017 Jan 3. doi: 10.1249/MSS.0000000000001196. [Epub ahead of print]
Authors: Thomas K, Dent J, Howatson G, Goodall S
Summary: We profiled the etiology and recovery of neuromuscular fatigue post-simulated-soccer-match-play. Fifteen semi-professional players completed a 90 min simulated soccer match. Pre-, immediately-post and at 24, 48 and 72 h participants completed a battery of neuromuscular, physical and perceptual tests. Perceived fatigue and muscle soreness were assessed via visual analogue scales. Maximum voluntary contraction (MVC) and twitch responses to electrical (femoral nerve) and magnetic (motor cortex) stimulation during isometric knee-extensor contractions and at rest were measured to assess central (voluntary activation, VA) and peripheral (quadriceps potentiated twitch force, Qtw,pot) fatigue, and responses to single and paired-magnetic stimuli were assessed to quantify corticospinal excitability and short-intracortical inhibition (SICI), respectively. Countermovement jump, reactive strength index and sprint performance were assessed to profile the recovery of physical function. Simulated match-play elicited decrements in MVC that remained unresolved at 72 h (P = 0.01). Central fatigue was prominent immediately post-exercise (-9% reduction in VA) and remained depressed at 48 h (-2%, P = 0.03). Qtw,pot declined by 14% post-exercise, remained similarly depressed at 24 h and had not fully recovered by 72 h post (-5%, P = 0.01). Corticospinal excitability was reduced at 24 h (P = 0.047) only, and no change in SICI was observed. Measures of jump performance and self-reported fatigue followed a similar time-course recovery to neuromuscular fatigue. Central processes contribute significantly to the neuromuscular fatigue experienced in the days post-soccer-match-play, but the magnitude and slower recovery of peripheral fatigue indicates that it is the resolution of muscle function that primarily explains the recovery of neuromuscular fatigue post- soccer match-play.

#4 Laterality related to the successive selection of Dutch national youth soccer players
Reference: J Sports Sci. 2017 Jan 6:1-5. doi: 10.1080/02640414.2016.1262544. [Epub ahead of print]
Authors: Verbeek J, Elferink-Gemser MT, Jonker L, Huijgen BC, Visscher C
Summary: In the general population, estimates of left-foot preference are around 20%. In soccer, specific tasks create positional demands, requiring 40% of the players to be left-footed. Whether and how this is related to the selection of players is unknown. To examine the successive selection of soccer players for Dutch national youth teams in relation to foot preference, 280 youth players (age = 16.2 ± 1.08 years) were monitored from the U16 through the U19 teams over the last 5 years. No difference in successive selection between left- and right-footed players was found (p < 0.05). Regardless of foot preference, more than 50% of the selected players were deselected out of a national youth team after 2 years. On average, 31% of the national youth players were left-footed, which is higher than expected, based on population estimates (χ2 (1) = 37.49, p < 0.001, w = 0.27). However, there was an under-representation of left-footed players, based on expected positional demands (i.e., attack, midfield, defence) (χ2 (1) = 16.83, p < 0.001, w = 0.18). The conclusion is that left-foot preference increases the probability of selection in Dutch national youth soccer teams.

#5 Energy Intake and Expenditure of Professional Soccer Players of the English Premier League: Evidence of Carbohydrate Periodization
Reference: Int J Sport Nutr Exerc Metab. 2017 Jan 4:1-25. doi: 10.1123/ijsnem.2016-0259. [Epub ahead of print]
Authors: Anderson L, Orme P, Naughton RJ, Close GL, Milsom J, Rydings D, O'Boyle A, Di Michele R, Louis J, Hambley C, Speakman JR, Morgans R, Drust B, Morton JP
Summary: In an attempt to better identify and inform the energy requirements of elite soccer players, we quantified the energy expenditure (EE) of players from the English Premier League (n=6) via the doubly labeled water method (DLW) over a 7-day in-season period. Energy intake (EI) was also assessed using food diaries, supported by the remote food photographic method and 24 h recalls. The 7-day period consisted of 5 training days (TD) and 2 match days (MD). Although mean daily EI (3186 ± 367 kcals) was not different from (P>0.05) daily EE (3566 ± 585 kcals), EI was greater (P<0.05) on MD (3789 ± 532 kcal; 61.1 ± 11.4 LBM) compared with TD (2956 ± 374 kcal; 45.2 ± 9.3 LBM, respectively). Differences in EI were reflective of greater (P<0.05) daily CHO intake on MD (6.4 ± 2.2 compared with TD (4.2 ± 1.4 Exogenous CHO intake was also different (P<0.01) during training sessions (3.1 ± 4.4 g.h-1) versus matches (32.3 ± 21.9 g.h-1). In contrast, daily protein (205 ± 30, P=0.29) and fat intake (101 ± 20, P=0.16) did not display any evidence of daily periodization. Although players readily achieve current guidelines for daily protein and fat intake, data suggest that CHO intake on the day prior to and in recovery from match play was not in accordance with guidelines to promote muscle glycogen storage.

#6 Anterior Inferior Iliac Spine Morphology and Outcomes of Hip Arthroscopy in Soccer Athletes: A Comparison to Nonkicking Athletes
Reference: Arthroscopy. 2016 Dec 31. pii: S0749-8063(16)30891-X. doi: 10.1016/j.arthro.2016.10.019. [Epub ahead of print]
Authors: Nawabi DH, Degen RM, Fields KG, Wentzel CS, Adeoye O, Kelly BT
Summary: The aim of the study was to describe the anterior inferior iliac spine (AIIS) morphology and clinical outcomes following arthroscopic surgical decompression in a group of high-level soccer athletes presenting with symptomatic hip impingement when compared with a control group of nonkicking athletes. From 2009 to 2012, we retrospectively reviewed our prospective hip registry for soccer athletes who underwent arthroscopic treatment for femoroacetabular impingement (FAI) with 2-year follow-up, comparing with a control group of nonkicking athletes. Demographics were collected and radiographic studies (plain radiograph and computed tomographic scan) reviewed for several parameters, including AIIS morphology. Patient-reported outcome scores, including modified Harris Hip Score (mHHS), Hip Outcome Score-Activities of Daily Living (HOS-ADL) and Sport-Specific Subscale (HOS-SSS), and International Hip Outcome Tool-33 (iHOT-33), were administered preoperatively, at 6 months, and at 1, 2, and 3 years postoperatively. Twenty-six soccer players (34 hips) and 87 nonkicking athletes (115) hips were identified. Demographics, including age (19.2 ± 4.1 vs 20.1 ± 3.8 years) and gender distribution (53.8% vs 51.7% male), were similar between the soccer and nonkicking athletes (P = .288, .849). Eighty-four percent of soccer players demonstrated some abnormality of the AIIS extending to (type II, 52%) or below the anterior acetabular rim (type III, 32%), compared with 52% nonkicking athletes (P < .001). At a mean follow-up of 35 months (range, 24-57 months) there was significant improvement in all outcome scores in both groups from pre- to postoperation (P < .001). There was no evidence of differences in outcome scores between groups (mHSS: 89 ± 14.6 vs 88.2 ± 14.4, P = .804; HOS-ADL: 94.1 ± 9.1 vs 92.2 ± 11.1, P = .431; HOS-SSS: 86 ± 17.1 vs 81.3 ± 24.3, P = .362) with the exception of iHOT-33 (81.7 ± 19 vs 70.3 ± 23.6, P = .027). High-level soccer players have a significantly higher rate of subspine impingement compared with nonkicking athletes. There should be a high index of suspicion when treating soccer players for FAI, where appropriate recognition and treatment of subspine impingement can yield excellent clinical results.

#7 Acute Effects of Three Neuromuscular Warm-Up Strategies on Several Physical Performance Measures in Football Players
Reference: PLoS One. 2017 Jan 6;12(1):e0169660. doi: 10.1371/journal.pone.0169660. eCollection 2017.
Authors: Ayala F, Calderon-Lopez A, Delgado-Gosalbez JC, Parra-Sanchez S, Pomares-Noguera C, Hernandez-Sanchez S, Lopez-Valenciano A, De Ste Croix M
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Summary: No studies have analysed the acute effects of the FIFA 11+ and Harmoknee warm-up programmes on major physical performance measures. The aim of this study was to analyse the acute (post-exercise) effects of the FIFA 11+, Harmoknee and dynamic warm-up routines on several physical performance measures in amateur football players. A randomized, crossover and counterbalanced study design was used to address the purpose of this study. A total of sixteen amateur football players completed the following protocols in a randomized order on separate days: a) FIFA 11+; b) Harmoknee; and c) dynamic warm-up (DWU). In each experimental session, 19 physical performance measures (joint range of motion, hamstring to quadriceps [H/Q] strength ratios, dynamic postural control, 10 and 20 m sprint times, jump height and reactive strength index) were assessed. Measures were compared via a magnitude-based inference analysis. The results of this study showed no main effects between paired comparisons (FIFA 11+ vs. DWU, Harmoknee vs. DWU and Harmoknee vs. FIFA 11+) for joint range of motions, dynamic postural control, H/Q ratios, jumping height and reactive strength index measures. However, significant main effects (likely effects with a probability of >75-99%) were found for 10 (1.7%) and 20 (2.4%) m sprint times, demonstrating that both the FIFA 11+ and Harmoknee resulted in slower sprint times in comparison with the DWU. Therefore, neither the FIFA 11+ nor the Harmoknee routines appear to be preferable to dynamic warm-up routines currently performed by most football players prior to training sessions and matches.

#8 Head injuries in children's football - results from two prospective cohort studies in four European countries
Reference: Scand J Med Sci Sports. 2017 Jan 4. doi: 10.1111/sms.12839. [Epub ahead of print]
Authors: Faude O, Rossler R, Junge A, Aus der Funten K, Chomiak J, Verhagen E, Beaudouin F, Dvorak J, Feddermann-Demont N
Summary: Head injuries are considered harmful in children. We analysed head and neck injuries in organised football in 7 to 12 year old children. Data for this analysis were obtained from a prospective cohort study over two consecutive football seasons in two European countries, and a randomised intervention trial over one season in four European countries. Football exposure and injuries were documented through an online database. Detailed information regarding injury characteristics and medical follow-up was retrieved from coaches, children and parents by phone. Thirty-nine head injuries and one neck injury (5% of all 791 injuries) were documented during 9,933 player-seasons (total football exposure 688,045 h). The incidence was 0.25 [95%CI 0.15, 0.35] head/neck injuries per 1,000 match hours (N=23 match injuries) and 0.03 [95%CI 0.02, 0.03] per 1,000 training hours. Eleven concussions (27.5%), nine head contusions (22.5%), eight lacerations or abrasions (20%), two nose fractures (2.5%) and two dental injuries (2.5%) occurred. The remaining eight injuries were nose bleeding or other minor injuries. Thirty injuries (75%) resulted from contact with another player, ten injuries were due to collision with an object, falling or a hit by the ball. Whereas 70% of all head injuries (N=28) were due to frontal impacts, 73% of concussions (N=8) resulted from an impact to the occiput. The incidence and severity of head injuries in children's football is low. Coaches and parents, however, should be sensitised regarding the potential of concussions, particularly after an impact to the occiput.

#9 Physiological, Perceptual and Performance Responses Associated With Self-Selected Versus Standardized Recovery Periods During a Repeated Sprint Protocol in Elite Youth Football Players: A Preliminary Study
Reference: Pediatr Exerc Sci. 2017 Jan 4:1-20. doi: 10.1123/pes.2016-0130. [Epub ahead of print]
Authors: Gibson N, Brownstein C, Ball D, Twist C
Summary: The purpose was to examine the physiological and perceptual responses of youth footballers to a repeated sprint protocol employing standardized and self-selected recovery. Eleven male participants (13.7 ± 1.1 years) performed a repeated sprint assessment comprising 10 x 30 m efforts. Employing a randomized crossover design, repeated sprints were performed using 30 s and self-selected recovery periods. Heart rate was monitored continuously with ratings of perceived exertion (RPE) and lower body muscle power measured 2 min after the final sprint. The concentration of blood lactate was measured at 2, 5 and 7 minutes post sprinting. Magnitude of effects were reported using effect size (ES) statistics ± 90% confidence interval and percentage differences. Differences between trials were examined using paired student t-tests (p < 0.05). Self-selected recovery resulted in most likely shorter recovery times (57.7%; ES 1.55 ± 0.5; p < 0.01), a most likely increase in percentage decrement (65%; ES 0.36 ±1 0.21; p = 0.12), very likely lower heart rate recovery (-58.9%; ES -1.10 ± 0.72; p = 0.05), and likely higher blood lactate concentration (p = 0.08-0.02). Differences in lower body power and RPE were unclear (p > 0.05). Self-selected recovery periods compromise repeated sprint performance.

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