Latest research in football - week 11 - 2019

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 A Preventive Model For Hamstring Injuries in Professional Soccer: Learning Algorithms
Reference: Int J Sports Med. 2019 Mar 14. doi: 10.1055/a-0826-1955. [Epub ahead of print]
Authors: Ayala F, López-Valenciano A, Gámez Martín JA, De Ste Croix M, Vera-Garcia FJ, García-Vaquero MDP, Ruiz-Pérez I, Myer GD
Summary: Hamstring strain injury (HSI) is one of the most prevalent and severe injury in professional soccer. The purpose was to analyze and compare the predictive ability of a range of machine learning techniques to select the best performing injury risk factor model to identify professional soccer players at high risk of HSIs. A total of 96 male professional soccer players underwent a pre-season screening evaluation that included a large number of individual, psychological and neuromuscular measurements. Injury surveillance was prospectively employed to capture all the HSI occurring in the 2013/2014 season. There were 18 HSIs. Injury distribution was 55.6% dominant leg and 44.4% non-dominant leg. The model generated by the SmooteBoostM1 technique with a cost-sensitive ADTree as the base classifier reported the best evaluation criteria (area under the receiver operating characteristic curve score=0.837, true positive rate=77.8%, true negative rate=83.8%) and hence was considered the best for predicting HSI. The prediction model showed moderate to high accuracy for identifying professional soccer players at risk of HSI during pre-season screenings. Therefore, the model developed might help coaches, physical trainers and medical practitioners in the decision-making process for injury prevention.

#2 Effects of Small-Sided Games vs. Conventional Endurance Training on Endurance Performance in Male Youth Soccer Players: A Meta-Analytical Comparison
Reference: Sports Med. 2019 Mar 13. doi: 10.1007/s40279-019-01086-w. [Epub ahead of print]
Authors: Moran J, Blagrove RC, Drury B, Fernandes JFT, Paxton K, Chaabene H, Ramirez-Campillo R
Summary: Small-sided games have been suggested as a viable alternative to conventional endurance training to enhance endurance performance in youth soccer players. This has important implications for long-term athlete development because it suggests that players can increase aerobic endurance through activities that closely resemble their sport of choice. The objectives of this meta-analysis were to compare male youth soccer players' adaptability to small-sided games vs. conventional endurance training and to establish exercise prescription guidelines for this population. The data sources utilised were Google Scholar, PubMed and Microsoft Academic. Studies were eligible for inclusion if interventions were carried out in male soccer players (aged < 18 years) and compared the effects of small-sided games and conventional endurance training on aerobic endurance performance. We defined small-sided games as "modified [soccer] games played on reduced pitch areas, often using adapted rules and involving a smaller number of players than traditional games". We defined conventional endurance training as continuous running or extensive interval training consisting of work durations > 3 min. The inverse-variance random-effects model for meta-analyses was used because it allocates a proportionate weight to trials based on the size of their individual standard errors and facilitates analysis whilst accounting for heterogeneity across studies. Effect sizes were represented by the standardised mean difference and presented alongside 95% confidence intervals. Seven studies were included in this meta-analysis. Both modes of training were effective in increasing endurance performance. Within-mode effect sizes were both of moderate magnitude [small-sided games: 0.82 (95% confidence interval 0.05, 1.60), Z = 2.07 (p = 0.04); conventional endurance training: 0.89 (95% confidence interval 0.06, 1.72), Z = 2.10 (p = 0.04)]. There were only trivial differences [0.04 (95% confidence interval - 0.36, 0.43), Z = 0.18 (p = 0.86)] between the effects on aerobic endurance performance of small-sided games and conventional endurance training. Subgroup analyses showed mostly trivial differences between the training methods across key programming variables such as set duration (≥ or < 4 min) and recovery period between sets (≥ or < 3 min). Programmes that were longer than 8 weeks favoured small-sided games [effect size = 0.45 (95% confidence interval - 0.12, 1.02), Z = 1.54 (p = 0.12)], with the opposite being true for conventional endurance training [effect size = - 0.33 (95% confidence interval - 0.79, 0.14), Z = 1.39 (p = 0.16)]. Programmes with more than 4 sets per session favoured small-sided games [effect size = 0.53 (95% confidence interval - 0.52, 1.58), Z = 0.98 (p = 0.33)] with only a trivial difference between those with 4, or fewer, sets [effect size = - 0.13 (95% confidence interval - 0.52, 0.26), Z = 0.65 (p = 0.52)]. Small-sided games are as effective as conventional endurance training for increasing aerobic endurance performance in male youth soccer players. This is important for practitioners as it means that small-sided games can allow both endurance and skills training to be carried out simultaneously, thus providing a more efficient training stimulus. Small-sided games offer the same benefits as conventional endurance training with two sessions per week, with ≥ 4 sets of 4 min of activity, interspersed with recovery periods of 3 min, recommended in this population.

#3 Management succession and success in a professional soccer team
Reference: PLoS One. 2019 Mar 13;14(3):e0212634. doi: 10.1371/journal.pone.0212634. eCollection 2019.
Authors: Kattuman P, Loch C, Kurchian C
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Summary: Research into sports team performance has shown that across many sports and league competitions, teams that change their coaches after a decline in performance do rebound, but fare no better on average than teams that have not changed their coach in a similar situation. A similar lack of succession benefits has been reported in studies of manager and CEO succession: it has not been established that changing a team's leader improves a declining team's performance. We study the effect of a change of coach on the performance of a professional soccer team. Based on rarely obtained access to a whole season (one year) of daily close observation of the team and coaching staff in practice and matches, this study uses quantitative and qualitative data to go beyond the "average" pattern reported in the literature. We document in detail how, in a single team case study over an entire season, the processes in leadership behavior changed with a change of coach, the effect this had on the state of mind of the team, how the match behaviors of the players changed, and how these changes translated into improved performance. The process effects of a leadership change on the performance of a sports team may hold insights for leader succession in management: in addition to the aggregate organizational and experience fit of the new team leader, the specific leadership processes introduced by the new leader are critical for performance effects.

#4 Prevalence and severity of traumatic dental injuries among young amateur soccer players: a screening investigation
Reference: Dent Traumatol. 2019 Mar 13. doi: 10.1111/edt.12470. [Epub ahead of print]
Authors: Qudeimat MA, AlHasan AA, AlHasan MA, Al-Khayat K, Andersson L
Summary: Traumatic dental injuries (TDI) are prevalent among soccer players. In Kuwait, no studies of TDI among soccer players have been carried out. The aim of this study was to investigate the prevalence, type, and causes of soccer-related traumatic dental injuries among 7-18-year-old amateur soccer players. All amateur soccer players who were registered in the 14 sports clubs in the country were invited to participate in this screening study. Players who were present in the club on the assigned examination day were included. The players were examined by two trained and calibrated paediatric dentists for signs of injury to the oral tissues. Injury diagnosis was made according to the Andreasen (2007) epidemiological dental injury classification. The history of any dental injury present at the time of examination was recorded. The timing and nature of any dental advice or treatment sought was also noted. Six hundred sixty-seven (48% inclusion rate) male players were included (mean age of 13.4 ± 2.6 years). In total, 213 injured teeth were observed among 169 (25%) players. The prevalence of soccer-related injuries was 11% and a greater number of injuries were observed in older players. Maxillary central incisors were the most frequently injured teeth (91%), and enamel-only fractures represented 60% of all injured teeth. Slightly more TDIs were soccer-related (44%) compared to non-soccer-related injuries (39%) and a large number of TDIs (39%) occurred inside the sports clubs. The prevalence of reported soft tissue injuries was 18%. The majority of the players (75%) did not receive dental care for their injuries. A significant number of young Kuwaiti amateur soccer players suffered TDIs. In addition, a high percentage of traumatic injuries were not treated, and there was a lack of the use of protective mouthguards.

#5 Effects of morning and nocturnal soccer matches on levels of some trace elements in young trained males
Reference: Cell Mol Biol (Noisy-le-grand). 2019 Feb 28;65(2):32-36.
Authors: Algul S, Bengu AS, Baltaci SB, Ozcelik O
Summary: The aim of this study was to comparatively evaluate effect of morning and nocturnal soccer matches induced metabolic stress on plasma levels of iron (Fe), copper (Cu) and zinc (Zn). Twenty male footballers performed two soccer matches in morning and at night on different days. Blood samples were taken before and after match. The levels of Fe, Zn and Cu were measured through an atomic absorption spectrophotometry. Metabolic stress was evaluated by altered malondialdehyde (MDA) levels that measured using High Performance Liquid Chromatography. In morning and at nocturnal soccer matches, levels of MDA (36% and 27%), Fe (37.4% and 38.9%) and Cu (34.8% and 26.8%) were all increased in all subjects, respectively. However, Zn level decreased -4.5 % in morning (n=10 subjects) and -9.4% at nocturnal (n=12 subjects) soccer matches. In addition, Cu/Zn ratio increased significantly 46.6% in morning and 36.6% at nocturnal soccer matches. Soccer match has significant effects on levels of MDA, Fe and Cu but not Zn levels. The results of this study showed that morning soccer match significantly alters levels of MDA and Cu and Cu/Zn ratio compared to nocturnal soccer match.

#6 A Comparison of Three Different Unilateral Strength Training Strategies to Enhance Jumping Performance and Decrease Inter-Limb Asymmetries in Soccer Players
Reference: Int J Sports Physiol Perform. 2019 Mar 12:1-26. doi: 10.1123/ijspp.2018-0920. [Epub ahead of print]
Authors: Gonzalo-Skok O, Moreno-Azze A, Arjol-Serrano JL, Tous-Fajardo J, Bishop C
Summary: This study compared the effects of performing different unilateral strength training interventions on unilateral and bilateral jumping performance and their related asymmetries in young soccer players. Forty-five male young (U-17) soccer players were randomly assigned to three eccentric overload training programs: The first group executed the same volume with both legs starting with the weaker leg (SVW, n=15), the second group carried out the double volume with the weaker leg and also starting with the weaker leg (DVW, n=15), and the third group performed the same volume with both legs starting with the stronger leg (SVS, n=15). Jumping performance assessment included a single-leg horizontal jump test, a triple single-leg horizontal jump test, a bilateral countermovement (CMJ) jump test and unilateral countermovement jump test. Asymmetries were also analyzed in the unilateral jumping tests. CMJ was improved (effect size [ES]: 0.27-0.48) and CMJ asymmetry was possibly reduced (ES: 0.08-0.24) in all groups. Substantial improvements were found in triple hop (ES: 0.52-0.71) in SVW and DVW, and triple hop asymmetry was substantially decreased (ES: 0.88) in DVW. Between-group analysis showed a substantial better performance in triple hop and horizontal hop with right leg in SVW and DVW compared to SVS. Unilateral strength training programs were shown to substantially improve bilateral jumping performance, while unilateral jumping was substantially enhanced in those groups that started the training session with the weaker leg. Finally, between-limbs asymmetries in the triple hop were mainly reduced through performing the double volume with the weaker leg.

#7 The Effects of Long Sprint Ability Oriented Small-Sided Games Using Different Players-to-Pitch Area on Internal and External Load in Soccer Players
Reference: Int J Sports Physiol Perform. 2019 Mar 12:1-23. doi: 10.1123/ijspp.2018-0645. [Epub ahead of print]
Authors: Castagna C, D'Ottavio S, Cappelli S, Póvoas SCA
Summary: The aim of this study was to examine the internal and external load imposed by Long Sprint Ability (LSA) oriented small-sided games (SSG) using different players-to-pitch area ratio (densities) in soccer players. Nineteen professional soccer players from the same soccer club (age 17.1±0.3 years, height 1.76±0.69 m, body mass 69.7±9.4 kg) participated in this study. Players performed 4x30s (150s recovery) all-out 1v1 SSG considering 300, 200 and 100 m2 per player (48h apart). Players' external-load was tracked with GPS technology (20Hz). Heart rate, blood lactate concentration (BLc) and rating of perceived exertion characterized players' internal-load. Peak BLc was assessed with a 30s all-out test on a non-motorized treadmill (NMT). SSG300 produced higher BLc than SSG200 (moderate) and SSG100 (large). The SSG300, SSG200 and SSG100 BLc were 97.8±34.8 (trivial), 74.7±24.9 (moderate) and 43.4±15.7% (large) of the NMT30s peak BLc, respectively. Players covered more distance at high-intensity during the SSG300 than in other SSG conditions (huge to very-large differences).. High-intensity deceleration distance was largely lower in SSG200 than in SSG300. SSG100 elicit very-large to huge and large to very-large lower external load values than SSG300 and SSG200, respectively. The main finding of this study showed an inverse association between ball-drill density and internal/external loads in LSA oriented SSG. The SSG300 attested to provide BLc closer to individual maximal, and thus, satisfying the all-out construct assumed for LSA development. Further studies using the SSG300 as training intervention and/or investigating other different SSG formats using the same density are warranted.

#8 Application of a Preventive Training Program Implementation Framework to Youth Soccer and Basketball Organizations
Reference: J Athl Train. 2019 Mar 11. doi: 10.4085/1062-6050-375-17. [Epub ahead of print]
Authors: Root HJ, Frank BS, Denegar CR, Casa DJ, Gregorio DI, Mazerolle SM, DiStefano LJ
Summary: Preventive training programs (PTPs) can reduce injury rates and improve neuromuscular control and sport performance. However, PTPs must be implemented correctly and consistently over time for athletes to benefit. Coaches represent the best long-term option for implementing PTPs. Youth athletes are at the optimal age for developing good habits before maturation. Although frameworks have been proposed to guide implementation efforts, little is known regarding the feasibility and real-world context of PTP implementation at the youth sport level. The aim was to evaluate the application of the 7-Step framework for promoting implementation of a preseason PTP workshop. Youth soccer and basketball organizations were utilized for this study. Organizations with at least 1 team of athletes aged 8 to 14 years were invited to participate in a free preseason coaches' education workshop on PTP implementation. The 7-Step framework was used to guide PTP education and implementation for each organization. Personnel at organizations that agreed to participate attended a single preseason workshop for coaches. Research staff were available as a resource throughout the season but did not actively implement or monitor the PTPs. Retrospective evaluation of each organization's completion of steps 1 through 5 of the 7-Step framework were used as main outcome measures.  A total of 62 youth soccer (n = 40) and basketball (n = 22) organizations were invited to participate. Twelve organizations completed steps 1 through 4 and steps 5a through 5d. The highest drop-off rate occurred during step 1, "Establishing Administrative Support". No organization completed all components of steps 1 through 5. To better understand how to successfully promote PTP adoption, we must identify the implementation steps that may present the most challenges. Because the highest drop-off rate was seen during the initial step, establishing administrative support and strengthening initial engagement are necessary to improve PTP implementation.

#9 Dissociation between changes in sprinting performance and Nordic hamstring strength in professional male football players
Reference:  PLoS One. 2019 Mar 14;14(3):e0213375. doi: 10.1371/journal.pone.0213375. eCollection 2019.
Authors: Suarez-Arrones L, Lara-Lopez P, Rodriguez-Sanchez P, Lazaro-Ramirez JL, Di Salvo V, Guitart M, Fuentes-Nieto C, Rodas G, Mendez-Villanueva A
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Summary: The aim of the present study was to evaluate the consequence of implementing a Nordic Hamstring exercise (NHE) protocol during the first 15 to 17 weeks of the season to assess the effect on sprinting and NHE strength (NHEs) in professional football players. The study examined 50 healthy male professional football players (age 18.8±0.8yr; height 176.8±6.9cm; weight 71.3±5.7kg) belonging to 3 of the reserve squads of three Spanish La-Liga clubs divided in 2 intervention teams [Nordic-Group1 (NG-1) and Nordic-Group2 (NG-2, extensive experience in NHE)] and 1 team as a control-group (CG). NHEs and linear sprint (T5, T10, T20-m) were evaluated at the beginning of the season and at the end of an intervention period of conditioning and football training, supplemented with a NHE protocol (24 sessions for NG-1 and 22 sessions for NG-2) or without using the NHE at all (CG). Sprint times were substantially improved in all groups (ES from -2.24±0.75 to -0.60±0.37). NHEs was enhanced absolute and relative to body-mass only in NG-1 after the training period (ES from 0.84±0.32 to 0.74±0.26), while in the NG-2 there were only improvements in average NHEs relative to body-mass (ES = 0.39±0.36). The improvements in T20-m were substantially greater in NG-2 vs. NG-1, and there were no differences in sprint performance changes between NG-1 and CG. Changes in sprinting performance and NHEs were unrelated. NHEs was largely correlated with the body-mass of the players. Results indicate that the improvements in sprint are not dependent on the NHEs changes, with no relationships between NHEs and sprint performance, and between sprint changes and changes in NHEs.

#10 Developing a theory-driven framework for a football intervention for men with severe, moderate or enduring mental health problems: a participatory realist synthesis
Reference: J Ment Health. 2019 Mar 12:1-12. doi: 10.1080/09638237.2019.1581339. [Epub ahead of print]
Authors: Such E, Burton H, Copeland RJ, Davies R, Goyder E, Jeanes R, Kesterton S, Mackenzie K, Magee J
Summary: Physical activity interventions are an important adjunct therapy for people with severe to moderate and/or enduring mental health problems. Football is particularly popular for men in this group. Several interventions have emerged over the past decade and there is a need to clearly articulate how they are intended to work, for whom and in what circumstances. The aim was to develop a theory-driven framework for a football intervention for men with severe, moderate and/or enduring mental health problems using a participatory realist approach. A participatory literature review on playing football as a means of promoting mental health recovery with a realist synthesis. It included the accounts and input of 12 mental health service users and the contributions of other stakeholders including football coaches and occupational therapists. Fourteen papers were included in the review. Analysis revealed that interventional mechanisms were social connectedness, identity security, normalising experiences and positive affectivity. These supported mental health recovery. Outcomes were moderated by social stigma and several interventional factors such as over-competitiveness. The context mechanism outcome configuration framework for these interventions map well onto social models of mental health recovery and provide insight into how they work. This now requires testing.

#11 Adductor squeeze test and groin injuries in elite football players: A prospective study
Reference: Phys Ther Sport. 2019 Mar 2;37:54-59. doi: 10.1016/j.ptsp.2019.03.001. [Epub ahead of print]
Authors: Moreno-Pérez V, Travassos B, Calado A, Gonzalo-Skok O, Del Coso J, Mendez-Villanueva A
Summary: The aim was to examining the relationship between hip adductor strength and groin injury incidence during the competitive season of professional football teams. Seventy-one players volunteered to participate. In the pre-season, maximal hip adductor strength was measured by means of the isometric adductor squeeze test. Hip adductor strength, normalized by body mass, was compared between players who suffered a groin injury (n = 18) vs uninjured players (n = 53). Risk ratios (RR) were used to evaluate the likelihood of players to suffer this type of injury. Most of the reported groin injuries occurred during competitive matches (5.5 per 1000 match hours). Maximal isometric hip adductor strength was lower in the groin-injured group compared with their uninjured counterparts (429.8 ± 100 vs 564 ± 58.7 N, d = -1.58 and 5.40 ± 1.27 vs 7.71 ± 0.89 N/kg, d = -1.88, respectively). Results revealed that values of maximal isometric adductor strength lower than 465.33 N increased the probability to suffer a groin injury by 72%. Furthermore, values of force relative to body mass lower than 6.971 N/kg increased the probability to suffer a groin injury by 83%. The assessment of Hip adductor strength, in addition to other measurements, might help practitioners to determine the probability of suffering an overuse groin injuries in elite football players.

#12 Application of multivariant decision tree technique in high performance football: The female and male corner kick
Reference: PLoS One. 2019 Mar 11;14(3):e0212549. doi: 10.1371/journal.pone.0212549. eCollection 2019.
Authors: Maneiro R, Casal CA, Ardá A, Losada JL
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Summary: The use of multidimensional statistical technique based on decision trees is of recent application in sports science. In the case of football, this technique has not yet been sufficiently proven. The aim of the present study was to search for different success models for the corners in the FIFA World Cup 2014 and FIFA Women's World Cup 2015. For this, the statistical analysis focused on the search for classification models for the different criteria considered (shot, shot between the three posts and goal), based on the creation of different decision trees that allow the most important variables to be identified quickly and efficiently. For this, 1117 corners were collected between the two competitions, performed in 116 international matches. It has been possible to establish multivariate models for the "shot" and "shot between the three posts" criteria, allowing, in some cases, to quadruple the potential for offensive success. On the other hand, we have been able to identify significant differences in the male and female model of execution. These findings suggest the need to continue deepening the study of tactical behavior in women's soccer from a multivariate perspective, and also propose a better optimization of the management and training of this type of actions for both male and female football. In addition, it has allowed to test the decision tree statistical technique in the analysis of high performance football, with satisfactory results and of great relevance in the applied field.

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