Latest research in football - week 50 - 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 Current Soccer Footwear, Its Role in Injuries and Potential for Improvement
Reference: Sports Med Int Open. 2018 May 25;2(2):E52-E61. doi: 10.1055/a-0608-4229. eCollection 2018 Apr.
Authors: Blanchard S, Palestri J, Guer JL, Behr M
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Summary: Soccer is the most popular sport in the world and generates great financial revenue. It is also a sport whose practice has evolved considerably in terms of intensity and commitment, and in which the intrinsic risk of injury (not directly related to an interaction with the environment) is particularly high. In this context, the cleated shoe as a major component of soccer equipment may play a key role in the overexposure to injury. Soccer shoe evolution is all the more challenging, because design and mechanical structure differ in many points compared to other modern shoes developed for sports such as running, tennis and basketball. This critical review aims to elucidate the characteristics of modern soccer footwear and their possible link to soccer-specific injuries, focusing on the following areas: (1) ergonomics, comfort and proprioception; (2) shoe mechanical characteristics; (3) field surfaces and shoe design.

#2 Does a bounding exercise program prevent hamstring injuries in adult male soccer players? - A cluster -RCT
Reference: Scand J Med Sci Sports. 2018 Dec 9. doi: 10.1111/sms.13353. [Epub ahead of print]
Authors: van de Hoef PAS, Brink MSM, Huisstede BMAB, van Smeden MM, de Vries NN, Goedhart EAE, Gouttebarge VV, Backx FJGF
Summary: Although the Nordic Hamstring Exercise (NHE) prevents hamstring injury in soccer players effectively, the annual incidence of these injuries still increases. This may be because of poor long-term compliance with the program. Furthermore, the timing and amplitude of gluteal and core muscle activation seem to play an important role in hamstring injury prevention, the NHE program was not designed to improve activation of these muscles. Therefore, we propose plyometric training as an alternative to reduce hamstring injuries soccer players. The purpose was to determine the preventive effect of the Bounding Exercise Program (BEP) on hamstring injury incidence and severity in adult male amateur soccer players. Thirty-two soccer teams competing in the first-class amateur league were cluster-randomized into the intervention or control group. Both groups were instructed to perform their regular training program, and the intervention group additionally performed BEP. Information about player characteristics was gathered at baseline and exposure, hamstring injuries and BEP compliance were weekly registered during one season (2016-2017). The data of 400 players were analyzed. In total, 57 players sustained 65 hamstring injuries. The injury incidence was 1.12/1000 hours in the intervention group and 1.39/1000 hours in the control group. There were no statistically significant differences in hamstring injury incidence (OR=0.89, 95% CI 0.46-1.75) or severity between the groups (p>0.48). In this large cluster-randomized controlled trial, no evidence was found for plyometric training in its current form to reduce hamstring injuries in amateur soccer players.

#3 Professional Soccer Players' Return to Play and Performance After Operative Repair of Achilles Tendon Rupture
Reference: Orthop J Sports Med. 2018 Nov 28;6(11):2325967118810772. doi: 10.1177/2325967118810772. eCollection 2018 Nov.
Authors: Trofa DP, Noback PC, Caldwell JE, Miller JC, Greisberg JK, Ahmad CS, Vosseller JT
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Summary: The majority of Achilles tendon ruptures are sports related; however, no investigation has examined the impact of surgical repair for complete ruptures on professional soccer players. The purpose was to examine the return to play, playing time, and performance of professional soccer players following Achilles tendon repair. Union of European Football Associations (UEFA) and Major League Soccer (MLS) athletes who sustained a primary complete Achilles tendon rupture and were treated surgically between 1988 and 2014 were identified via public injury reports. Demographic information and performance-related statistics for the identified athletes were recorded for the season before surgery and 2 seasons after surgery and were compared with information for matched controls. Statistical analyses were used to assess differences in recorded metrics. A total of 24 athletes with Achilles ruptures met inclusion criteria, 17 (70.8%) of whom were able to return to play. On average, players had 8.3 years of professional-level experience prior to sustaining an Achilles rupture. Among athletes who returned to play, no differences were found in the number of games played or started, minutes played, or goals scored 1 year postoperatively compared with the year prior to injury. However, 2 years postoperatively, these athletes played 28.3% (P = .028) fewer minutes compared with their preoperative season, despite starting and playing in an equivalent number of games. Matched controls had baseline playing time and performance statistics similar to those of players. However, controls played and started in significantly more games and played more minutes at 1 and 2 years compared with players (P < .05). No differences were found in goals scored at any time point. This is the first investigation examining the effect of an Achilles repair on the career of professional soccer players. This is a difficult injury that most commonly occurs in veteran players and prevents 29.2% of players from returning to play despite surgical management. Additionally, athletes able to return to play were found to play fewer minutes 2 years postoperatively compared with their baseline as well as playing less at 1 and 2 years postoperatively compared with uninjured matched controls. The reduction in playing time following an Achilles repair has significant implications for professional players and teams.

#4 Changes in Echocardiographic Parameters among Beninese Soccer Referees during the Division 1 Championship in 2016
Reference: J Sports Med (Hindawi Publ Corp). 2018 Nov 7;2018:6024574. doi: 10.1155/2018/6024574. eCollection 2018.
Authors: Coffi Q, Arnaud S, Polycarpe G, Hyacinthe A, Folly M, Basile N, Murielle H, Martin HD
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Summary: The goal of this study was to describe the echocardiographic parameters of soccer referees and to examine the changes in these parameters after a period of intensive physical exercise. We conducted a prospective study that included Beninese soccer referees. The study of the geometry and function of the left ventricle (LV) was made at the beginning and end of the national Division 1 championship, which was held during the course of 10 weeks. There were 37 referees included in this study; 20 at the national level (G1: 27.8 ± 6.6 years) and 17 at the international level (G2: 32.1 ± 6.4 years). Dimensions of the LV were normal for all the referees. At the beginning of the championship, 51.3% of the referees had a normal LV geometry, 37.8% had concentric remodelling, 2.7% had concentric hypertrophy, and 8.1% had eccentric hypertrophy. In the group of referees with normal LV geometry, a modification in concentric remodelling at the end of the championship was seen in 30% of the referees in G1, 33.3% of the referees in G2, and 31.6% of the whole sample. In the group of subjects who presented concentric LV remodelling, a modification in the normal geometry was observed in 37.5% of those in G1, in 0% of those in G2, and in 21.4% of the whole sample. The cases of LV hypertrophy showed no change regardless of the group considered. An LV ejection fraction of more than 50% and an E/E' ratio less than 8 were found in all referees. All the referees studied had normal cardiac morphology and function. The intensity of the physical load was insufficient to impact this morphology.

#5 In-season training load quantification of one-, two- and three-game week schedules in a top European professional soccer team
Reference: Physiol Behav. 2018 Dec 6. pii: S0031-9384(18)30585-7. doi: 10.1016/j.physbeh.2018.11.036. [Epub ahead of print]
Authors: Oliveira R, Brito J, Martins A, Mendes B, Calvete F, Carriço S, Ferraz R, Marques M
Summary: Top European soccer teams that play in UEFA competitions often participate in one, two- or three-games per week. Therefore, it is necessary to understand the variations in training load (TL) according to each team's competitive schedule. The aim of this study was to quantify internal and external TLs within five microcycles: M4 and M5 - one-game weeks; M1 and M3 - two-game weeks; M2 - three-game week). The sample consisted of thirteen elite soccer players. A global positioning system (GPS) was used to measure the total distance covered and distances of different exercise training zones (1-5), the session ratings of perceived exertion (s-RPE) scores and the amount of creatine kinase (CK) created during daily training sessions for the 2015-2016 in-season period. The data were analysed with respect to the number of days prior to a given match. The main results indicate that there was a significant difference in training intensity for zone 1 between M5 and M3 (4010.2 ± 103.5 and 4507.6 ± 133.0 m, respectively); a significant difference in training intensity for zone 3 between M4 and M2 (686.1 ± 42.8 and 801.2 ± 61.2 m, respectively); a significant difference in the duration of the training sessions and matches between M5 and M2 (69.2 ± 2.1 and 79.6 ± 2.3) and M1 and M2 (69.7 ± 1.0 and 79.6 ± 2.3); and finally, there was a significant difference in CK between M1 and M5 (325.5 ± 155.0 and 194.4 ± 48.9). Moreover, there was a significant decrease in TL in the last day prior to a match, for all microcycles and all variables. There was no significant difference with respect to s-RPE. This study provides the first report of daily external and internal TLs and weekly accumulated load (training sessions and match demands) during one, two, and three-game week schedules in a group of elite soccer players. Expected significant differences are found in daily and accumulated loads for within- and between-game schedules. A similar pattern is exhibited for one- and two-game week microcycles regarding the day before the match, which exhibits a decrease in all variables.

#6 Estimating fat-free mass in elite youth male soccer players: cross-validation of different field methods and development of prediction equation
Reference: J Sports Sci. 2018 Dec 11:1-8. doi: 10.1080/02640414.2018.1551045. [Epub ahead of print]
Authors: Munguía-Izquierdo D, Suárez-Arrones L, Di Salvo V, Paredes-Hernández V, Ara I, Mendez-Villanueva A
Summary: This study determined the most effective field method for quantifying fat-free mass (FFM) in elite youth male soccer players compared to dual X-ray absorptiometry (DXA) values and to develop prediction equations for FFM based on anthropometric variables. Forty-one male elite-standard youth soccer players, ages 16.2-18.0 years, undertook FFM assessments including bioelectrical impedance analysis, and different skinfold-based prediction equations. DXA provided a criterion measure of FFM. Correlation coefficients, bias, limits of agreement, and differences were used as validity measures, and regression analyses to develop soccer-specific prediction equations. Slaughter et al (1988), Durnin and Wormersley (1974), and Sarria et al (1998) equations showed the lowest biases, and no significant, standardized, and substantial differences against DXA. The new youth soccer-specific anthropometric equation explained 91% of the DXA-derived FFM variance using three circumferences, eight skinfolds, and one bone breadth. All field methods compared in this study may not be adequate for estimating FFM in elite youth male soccer players, except the equations of Slaughter et al (1988), Durnin and Wormersley (1974), and Sarria et al (1998). We recommend the use of the new soccer-specific equation proposed in this study as a valid alternative to DXA to quantify FFM among elite youth male players.

#7 Dynamic and Static Assessment of Single Leg Postural Control in Female Soccer Players
Reference: J Sport Rehabil. 2018 Dec 11:1-19. doi: 10.1123/jsr.2018-0072. [Epub ahead of print]
Authors: Meiners KM, Loudon JK
Summary: Various methods are available for assessment of static and dynamic postural stability. The purpose of this study was to investigate the relationship between dynamic postural stability as measured by the Star Excursion Balance Test (SEBT) and static postural sway assessment as measured by the Technobody™ Prokin in female soccer players. A secondary purpose was to determine side-to-side symmetry in this cohort. 18 female soccer players completed testing on the SEBT and TechnobodyTM Prokin balance device. Outcome measures were: anterior, posterior medial, and posterior lateral reaches from the SEBT and Center of Pressure (COP) in the X and Y axis and Standard Deviation of movement in the forward-backward and medial-lateral directions from the force plate on left and right legs. Bivariate correlations were determined between the 8 measures. Additionally, paired Wilcoxon Signed Ranks were performed to determine similarity between limb scores. All measures on both the SEBT and postural sway assessment were significantly correlated when comparing dominant to non-dominant lower extremities with exception of SD of movement in both X and Y axis. When correlating results of the SEBT with postural sway assessment, a significant correlation was found between SEBT right lower extremity posterior lateral reach (r=.567, p<.05) and summed SEBT (r=.486, p<.05) and the COP in the Y axis. A significant correlation was also found on the left lower extremity, with Standard Deviation of movement forward-backward and SEBT posterior medial reach (r=-.511, p<.05). Dynamic postural tests and static postural tests provide different information to the overall assessment of balance in the female soccer player. Relationship between variables differed based on the subject's lower extremity dominance.

#8 Validation study of the Functional Assessment Scale for Acute Hamstring injuries in Spanish professional soccer players
Reference: Clin Rehabil. 2018 Dec 10:269215518815540. doi: 10.1177/0269215518815540. [Epub ahead of print]
Authors: Hernández-Sanchez S, Korakakis V, Malliaropoulos N, Moreno-Perez V
Summary: The purpose of the study was to cross-culturally adapt and validate the Functional Assessment Scale for acute hamstring injury for professional Spanish-speaking soccer players. Clinical measurement study. Cross-cultural adaptation was conducted following international recommendations. Indicators of validity, reliability and responsiveness are provided. The Spanish version of the Functional Assessment Scale for acute hamstring injury scale was administered to 165 participants: 45 professional soccer players with acute hamstring muscle injury diagnosis, 40 healthy subjects, 40 individuals at-risk for a hamstring muscle injury and 40 patients with injuries of the lower limb other than hamstring muscle injury. The Functional Assessment Scale for acute hamstring injury were main outcome measures. Spanish version of the Quality of Life Short-Form 36 questionnaire (SF-36) and the Lower Limb Functional Index (LLFI) were used as the reference measures. Cronbach's alpha (internal consistency) for the Spanish version of the Functional Assessment Scale for acute hamstring injury scale was >0.8. The intraclass correlation coefficient using the two-way random model (ICC2,1) (test-retest) was 0.993 (95% confidence interval (CI): 0.991-0.995; P < 0.05). In the exploratory factor analysis, a one-factor solution explained 85% of the variance. Subjects with hamstring muscle injury scored significantly lower than the other groups in the Spanish version of the Functional Assessment Scale for acute hamstring injury scale ( P < 0.001). The Spanish version of the Functional Assessment Scale for acute hamstring injury scale score within the hamstring muscle injury group showed moderate and significant correlations with SF-36 physical components (Spearman's rs > 0.6; P < 0.001), and LLFI score at baseline ( rs = 0.42; P < 0.01). The standard error of measurement (SEM) and minimum detectable change threshold (MDC95%) were 2.6 and 7.2 points, respectively. The responsiveness indicators have an effect size of 3.62, and the standardized response mean is 3.24. The Spanish version of the Functional Assessment Scale for acute hamstring injury scale showed satisfactory psychometric properties. It can be considered a reliable and valid instrument to assess the functional impact of acute hamstring muscle injury in professional Spanish-speaking football players.

#9 Effective But Not Adhered to: How Can We Improve Adherence to Evidence-Based Hamstring Injury Prevention in Amateur Football?
Reference: Clin J Sport Med. 2018 Dec 13. doi: 10.1097/JSM.0000000000000710. [Epub ahead of print]
Authors: van der Horst N, Hoef SV, Otterloo PV, Klein M, Brink M, Backx F
Summary: The purpose was to investigate adherence to a Nordic hamstring exercise (NHE) program in a real-world context of male amateur football, and the perceptions of end users (players) and intervention deliverers (coaches and medical staff) about adherence to this proven effective program.
Dutch amateur football. Two hundred sixty-four players, 23 coaches, and 29 medical staff from Dutch amateur football teams that participated in a national randomized controlled trial 2 years earlier. Nordic hamstring exercise program were used as the independent variable. Main outcome measures were the Nordic hamstring exercise program adherence during 2014 and 2015. Intervention or control group allocation during the trial, transfers, and personal perception about adherence to the program were also examined. Of all players, 69% reported never, 16% sometimes, 6% frequently, 5% often, and 4% always performing exercises of the NHE program. Adherence to the NHE program was higher among players who had been in the NHE arm of the previous trial and among players who had not been transferred to another club compared with players who had been transferred. Key factors in stimulating players to adhere to the NHE program were knowledge of the NHE and personal motivation. Coaches and medical staff members also mentioned personal motivation and consensus with team staff as key factors to encourage NHE adherence. Among high-level male amateur football players, adherence to an evidence-based hamstring injury-prevention program was very low. It is essential to recognize factors that stimulate or limit adherence to injury-prevention programs for effective programs to actually lead to a reduction in hamstring injuries in a real-world context.

#10 Does Night-Training Load Affect Sleep Patterns and Nocturnal Cardiac Autonomic Activity in High-Level Female Soccer Players?
Reference: Int J Sports Physiol Perform. 2018 Dec 20:1-26. doi: 10.1123/ijspp.2018-0652. [Epub ahead of print]
Authors: Costa JA, Brito J, Nakamura FY, Oliveira EM, Costa OP, Rebelo AN
Summary: The purpose was to analyse whether exercise training conducted at night disturbs sleep and affects nocturnal cardiac autonomic control in high-level female athletes. Eighteen high-level female soccer players (mean±SD; age: 20.4±2.1 years) wore actigraphs and heart rate (HR) monitors during night-sleep throughout night-training days (n=8) and resting days (n=8), for 3 consecutive weeks. This was a longitudinal study that measured internal training load, sleep, nocturnal cardiac autonomic activity, and well-being ratings prior to training sessions. Training load varied across training days (e.g., training impulse range; mean±SD; ES [95% confidence interval]: 72.9±18.8 to 138.4±29.6 a.u.; F(4,62)=32.331; ηp2=0.673 [0.001-0.16], large effect; p<0.001). However, no differences in subjective well-being ratings were observed, although ES was large. Total sleep time (training days vs. resting days: 7:17±0:47 hours vs. 7:51±0:42 hours; ES=0.742 [0.59-0.92], p=0.005; moderate effect) and sleep onset time (00:58±0:19 vs. 00:44±0:16 hours; ES=0.802 [0.68-0.94], p=0.001; moderate effect) were negatively affected after night-training. In addition, small effects were detected for wake up time, time in bed, and sleep latency (p>0.05). No differences were detected in HR variability (HRV) during sleep (range of lnRMSSD: 4.3±0.4 to 4.5±0.4 ln[ms] vs. 4.6±0.3 to 4.5±0.4 ln[ms]; F(3,52)=2.148; p>0.05; ηp2=0.112 [0.01-0.25], medium effect), but the HR during sleep was significantly higher after training days (range of HR: 56±4 to 63±7 vs. 54±4 to 57±6 b.p.m; F(2,32) = 15.956; p<0.001 ηp2=0.484 [0.20-0.63], large effect). Overall, the results indicate that exercise training conducted at night may disturb sleep and affect HR, whereas limited effects can be expected in HRV assessed during sleep in high-level female soccer players.

#11 Modelling the Prediction of the Session Rate of Perceived Exertion in Soccer: Unravelling the Puzzle of Predictive Indicators
Reference: Int J Sports Physiol Perform. 2018 Dec 20:1-22. doi: 10.1123/ijspp.2018-0698. [Epub ahead of print]
Authors: Geurkink Y, Vandewiele G, Lievens M, de Turck F, Ongenae F, Matthys SPJ, Boone J, Bourgois JG
Summary: This study aimed to predict the session Rate of Perceived Exertion (sRPE) in soccer and determine the main predictive indicators of the sRPE. A total of 70 External Load Indicators (ELIs), Internal Load Indicators (ILIs), Individual Characteristics (ICs) and Supplementary Variables (SVs) were used to build a predictive model. The analysis using Gradient Boosting Machines showed a mean absolute error (MAE) of 0.67 ± 0.09 AU and a Root Mean Squared Error (RMSE) of 0.93 ± 0.16 AU. ELIs were found to be the strongest predictors of the sRPE, accounting for 61.5% of the total normalized importance (NI), with total distance as the strongest predictor. The included ILIs and ICs accounted only for respectively 1.0% and 4.5% of the total NI. Predictive accuracy improved when including SVs such as group-based sRPE-predictions (10.5% of NI), individual deviation variables (5.8% of NI) and individual player markers (17.0% of NI). The results showed that the sRPE can be predicted quite accurately, using only a relatively limited number of training observations. ELIs are the strongest predictors of the sRPE. It is however useful to include a broad range of variables, other than ELIs, because the accumulated importance of these variables account for a reasonable component of the total normalized importance. Applications resulting from predictive modelling of the sRPE can help the coaching staff to plan, monitor and evaluate both the external and internal training load.

#12 Data-Driven Visual Performance Analysis in Soccer: An Exploratory Prototype
Reference: Front Psychol. 2018 Dec 5;9:2416. doi: 10.3389/fpsyg.2018.02416. eCollection 2018.
Authors: Benito Santos A, Theron R, Losada A, Sampaio JE, Lago-Peñas C
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Summary: In soccer, understanding of collective tactical behavior has become an integral part in sports analysis at elite levels. Evolution of technology allows collection of increasingly larger and more specific data sets related to sport activities in cost-effective and accessible manner. All this information is minutely scrutinized by thousands of analysts around the globe in search of answers that can in the long-term help increase the performance of individuals or teams in their respective competitions. As the volume of data increases in size, so does the complexity of the problem and the need for suitable tools that leverage the cognitive load involved in the investigation. It is proven that visualization and computer-vision techniques, correctly applied to the context of a problem, help data analysts focus on the relevant information at each stage of the process, and generally lead to a better understanding of the facts that lie behind the data. In the current study, we presented a software prototype capable of assisting researchers and performance analysts in their duty of studying group collective behavior in soccer games and trainings. We used geospatial data acquired from a professional match to demonstrate its capabilities in two different case studies. Furthermore, we successfully proved the efficiency of the different visualization techniques implemented in the prototype and demonstrated how visual analysis can effectively improve some of the basic tasks employed by sports experts on their daily work, complementing more traditional approaches.

#13 When Something Is at Stake: Differences in Soccer Performance in 11 vs. 11 During Official Matches and Training Games
Reference: J Strength Cond Res. 2019 Jan;33(1):167-173. doi: 10.1519/JSC.0000000000002936.
Authors: Olthof SBH, Frencken WGP, Lemmink KAPM
Summary: Training games are used to mimic the official match, but differ in playing duration and a consequence of winning or losing. Anxiety levels, crowd pressure, and the intention to win are examples of constraints present in the match, but absent or less prevalent in training. The aim is, therefore, to compare soccer performance in official matches with 11 vs. 11 training games. Six elite youth soccer teams played 5 official matches and 15 training games. Soccer performance, defined as a combination of game characteristics (game duration, transitions, and ball possession duration) and physical (distance covered, high-intensity distance, and sprints), technical (passing), and team tactical performance (inter-team and intra-team distances) and corresponding interaction patterns, was determined with video footage and positional data (local position measurement system). Soccer performance in official matches differed from similar training games, in a way that players covered more distance, sprinted more often, but game pace was lower and players made more mistakes. In addition, team width was smaller and length-per-width ratio larger and teams were tighter coupled in official matches. 11 vs. 11 training games can be used to mimic the match, in particular the team tactical performance. Coaches could increase physical and technical representativeness of training games by raising the stakes and increasing the consequence of winning or losing.

#14 The influence of short-term fixture congestion on position specific match running performance and external loading patterns in English professional soccer
Reference: J Sports Sci. 2018 Dec 18:1-9. doi: 10.1080/02640414.2018.1558563. [Epub ahead of print]
Authors: Jones RN, Greig M, Mawéné Y, Barrow J, Page RM
Summary: The aim of the current study was to investigate positional specific physical performance and external load responses to short term fixture congestion in English professional soccer. A total of 515 match observations were categorised as G1: the first game in a week with >4 days following a previous game, G2: the second game in a week played <4 days since G1, and G3: the third game in a week played with <4 days between each of the previous games. Global positioning system and accelerometer-based metrics were partitioned into fifteen-minute epochs. These data were then analysed using a linear mixed model to assess both the within and between game positional differences. Total, low-intensity (<4.0 m·s-1), medium-intensity (MID; 4.0-5.5 m·s-1), and sprint distance (>7.0 m·s-1) were significantly different across games. No between game positional differences were identified; however, within match position specific differences were observed for measures of MID and HID. No significant differences were evident for accelerometer derived metrics between games or across positions. The current data suggests that the use of fifteen minute within game epochs enables the detection of alterations in physical output during congested schedules. The observed within game positional differences has implications for player specific conditioning and squad rotation strategies.

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