Latest research in football - week 19 - 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 Bone geometry in young male and female football players: a peripheral quantitative computed tomography (pQCT) study
Reference: Arch Osteoporos. 2018 May 8;13(1):57. doi: 10.1007/s11657-018-0472-2.
Authors: Lozano-Berges G, Matute-Llorente ÁA, Gomez-Bruton A, Gonzalez-Aguero A, Vicente-Rodriguez G, Casajus JA
Summary: The present study shows that football practice during growth may improve bone geometry in male and female football players. However, only females had better bone strength in comparison with controls. The aim of this study was to compare bone geometry in adolescent football players and controls. A total of 107 football players (71 males/36 females; mean age 12.7 ± 0.6/12.7 ± 0.6 years) and 42 controls (20 males/22 females; mean age 13.1 ± 1.4/12.7 ± 1.3 years) participated in this study. Total and trabecular volumetric bone mineral content (Tt.BMC/Tb.BMC), cross-sectional area (Tt.Ar/Tb.Ar), and bone strength index (BSI) were measured at 4% site of the non-dominant tibia by peripheral quantitative computed tomography (pQCT). Moreover, Tt.BMC, cortical BMC (Ct.BMC), Tt.Ar, cortical Ar (Ct.Ar), cortical thickness (Ct.Th), periosteal circumference (PC), endosteal circumference (EC), fracture load in X-axis, and polar strength strain index (SSIp) were measured at 38% site of the tibia. Multivariate analyses of covariance were used to compare bone pQCT variables between football players and controls using the tibia length and maturity offset as covariates. Female football players demonstrated 13.8-16.4% higher BSI, Ct.Th, fracture load in X-axis, and SSIp than controls (p < .0036). Males showed no significant differences in bone strength when compared to controls (p > .0036). In relation to bone mineral content and area, male football players showed 8.8% higher Tt.Ar and Tb.Ar at the 4% site of the tibia when compared to controls; whereas 13.8-15.8% higher Tt.BMC, Ct.BMC, and Ct.Ar at the 38% site of the tibia were found in female football players than controls (p < .0036). In this study, female adolescent football players presented better bone geometry and strength values than controls. In contrast, only bone geometry was higher in male football players than controls.

#2 Physical preparation of the football player with an intramuscular hamstring tendon tear: clinical perspective with video demonstrations
Reference: Br J Sports Med. 2018 May 3. pii: bjsports-2017-098817. doi: 10.1136/bjsports-2017-098817. [Epub ahead of print]
Authors: Taberner M, Cohen DD
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#3 "What is the score?" A review of football-based public mental health interventions
Reference: J Public Ment Health. 2017;16(4):144-158. doi: 10.1108/JPMH-03-2017-0011. Epub 2017 Dec 18.
Authors: Friedrich B, Mason OJ
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Summary: Football exercise as an intervention for people with severe mental health problems has seen an increasing interest in the past years. To date, there is, however, no comprehensive review of the empirical evidence regarding the effectiveness of these interventions. In this review, the authors have comprised the research findings from the peer-review literature as well as the theoretical approaches to football exercise as an adjunct treatment. This overview will be informative to everybody who is planning to develop a football intervention for this population as well as to the people who are preparing evaluation studies that measure the effectiveness of such interventions. The paper aims to discuss these issues. The authors identified research papers in the peer-review literature that feature empirical findings on "football interventions" that aim at improving mental and/or physical well-being in participants with mental health problems. The authors are using the term "football intervention" here in the sense that the participants actively took part in football exercise, so the authors excluded studies in which the participants only watched football or used football as a metaphor to discuss mental health problems. In a table, the authors indicate the definition of the target group, targeted outcomes, measured outcomes, form and frequency of the intervention as well as the research method(s). The authors identified 16 studies on 15 projects. The majority of studies were qualitative and had positive findings in which the participants reported increased well-being and connectedness, elevation of symptoms and improved physical well-being. The outcomes of the quantitative studies, however, were mixed with some results suggesting that not all intended goals were achieved. There seems to be a need for more quantitative studies to triangulate the qualitative findings. Interestingly, most interventions take place in the UK. Many studies fail to give detailed methodological information and often the aims of the interventions are vague or not stated at all. Due to the heterogeneity of the studies and relative scarcity of evaluation projects on football interventions for people with mental health problems, the authors could not conduct an in-depth systematic review. Furthermore, the information on methods was often unsatisfying and despite efforts to get more detailed input from the authors of cited papers, those gaps could not always be filled. Instead of coming up with a crystal-clear summary of whether and how football interventions work for everybody, topics were identified that need to be addressed in the planning of interventions, in evaluation studies, in implementation efforts and in the theoretical discourse. This paper constitutes a helpful overview for everybody who is interested in the theoretical background of football interventions for people with mental health problems, for people who are planning to develop respective interventions, for researchers who engage in evaluation projects that look into the effectiveness of football interventions (or similar exercise interventions) as well as for the people who are interested in how football interventions can be implemented. This paper is likely to make a contribution to the advancement of alternative exercise interventions that aim at improving mental, physical and social health in people with mental health problems. This paper will help putting the topic of football interventions (and similar, alternative exercise interventions) further up on the public health agenda by providing an overview of the empirical evidence at hand and by specifying advantages of the approach as well as pointing out actions that need to be taken to make football a recognised, evidence based and viable option for adjunct mental health treatment that is attractive to potential participants as well as funders as well as to the potential participants. There is no comprehensive summary to date that provides a (reasonably) systematic overview of empirical findings for football interventions for people with MH problems. Furthermore, the literature on the theoretical background of these interventions has been somewhat patchy and heterogonous. This paper aims at filling both these gaps and identifies the issues that need to be covered in the planning of respective interventions and evaluations. This paper will be useful to everybody who is developing football interventions (or similar alternative adjunct exercise interventions), who is conducting evaluation research in this area and who is interested in the implementation of football interventions.

#4 The effects of short term detraining and retraining on physical fitness in elite soccer players
Reference: PLoS One. 2018 May 10;13(5):e0196212. doi: 10.1371/journal.pone.0196212. eCollection 2018.
Authors: Joo CH
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Summary: The aim of this study was to examine the effects of aerobic high-intensity training with reduced volume and training cessation on body composition and physical fitness after the end of season and the time required to recapture physical fitness with intensified retraining following two weeks of detraining in elite soccer players. Twenty male semi-professional soccer players participated in this study. The soccer players were assigned to either a group that completed high-intensity aerobic training (HAT, n = 10) or to a detraining and retraining group (DHAT, n = 10) for a 5-week period immediately after the end of the season. The first 2 weeks of the period, members of the HAT group performed high-intensity aerobic exercise (80-90% of HRmax, 12 min × 3, three times per week), whereas members of the DHAT group abstained from any physical activity. During the subsequent 3 weeks, members of both the HAT and DHAT groups completed high-intensity aerobic exercise. Exercise performance testing and body composition analysis were performed before; after 2 weeks of detraining; and at 1, 2 and 3 weeks of retraining. Intensified high-intensity training for 5 weeks maintained the performance in the Yo-Yo Intermittent Recovery level 2 test (Yo-Yo IR2) and repeated sprints at any time point (P > 0.05). However 2 weeks of detraining resulted in significant decreases in the performance on the Yo-Yo IR2 (P < 0.01) and repeated sprints test (P < 0.05). Performance on the Yo-Yo IR2 enhanced after 2 weeks of retraining and was maintained up to 3 weeks after retraining, with no significant differences between conditions (P > 0.05). In addition, repeated sprint performance markedly decreased after the detraining period (P < 0.05) and was continuously lower compared to the baseline at 2 weeks after retraining (P < 0.05). Furthermore, this value reached baseline level at the end of the experimental period (P > 0.05). There were no significant differences between conditions in body composition, performance of agility, or sprint ability throughout the 5-week experimental period (P > 0.05). The present data suggest that short-term detraining after the competitive season can markedly decrease performances in the Yo-Yo IR2 test and repeated sprints. To return to a previous level of ability on the Yo-Yo IR2 and/or sprint test with retraining through high-intensity aerobic training after a period of detraining, a similar or longer period of retraining is required. However, the high-intensity training with reduced amount of training after competitive season can prevent reductions in physical fitness.

#5 Angle-Specific Isokinetic Metrics Highlight Strength Training Needs of Elite Youth Soccer Players
Reference: J Strength Cond Res. 2018 May 2. doi: 10.1519/JSC.0000000000002612. [Epub ahead of print]
Authors: Eustace SJ, Page RM, Greig M
Summary: The purpose of this study was to assess traditional and angle-specific isokinetic strength of eccentric knee flexors (eccKFs) and concentric knee extensors (conKEs) between senior professional and youth soccer players. Thirty-four male soccer players (17 senior and 17 youth) were recruited for bilateral assessments at 180, 270, and 60°·s. Peak torque (PT), dynamic control ratio (DCR), angle of peak torque (APT), functional range (FR), angle-specific torque (AST), and angle-specific DCR (DCRAST) were compared. The eccentric knee flexor (eccKF) and conKE PT (p = 0.782) and DCR (p = 0.508) were not different between groups across all angular velocities. Significant differences were identified for eccKF APT (p = 0.018) and FR (p = 0.006), DCRAST at 270°·s (p = 0.031), and in AST data recorded across angular velocities for eccKF and conKE (p = 0.003). Traditional strength measures were not sensitive to playing age, with implications for misinterpretation in training prescription. By contrast, AST data did differentiate between ages. Strength deficits that highlight the muscle contraction type, angular velocity, and joint angle can be manipulated within an individualized training intervention. Given the relevance to injury etiology, this study highlights potential implications for improved assessment strategies to inform training prescription for performance and injury prevention. Given the high number of injuries in adolescent soccer players, and in line with previous recommendations, practitioners should consider using more informed and specific strength and conditioning practices at younger ages.

#6 Dose-Response Relationship between Training Load and Changes in Aerobic Fitness in Professional Youth Soccer Players
Reference: Int J Sports Physiol Perform. 2018 May 10:1-22. doi: 10.1123/ijspp.2017-0843. [Epub ahead of print]
Authors: Fitzpatrick JF, Hicks KM, Hayes PR
Summary: The aim of this study was to compare the dose-response relationship between, traditional arbitrary speed thresholds versus an individualised approach, with changes in aerobic fitness in professional youth soccer players. Fourteen youth soccer players, completed a 1500 metre time trial to estimate maximal aerobic speed (km.h-1, (MAS)) at the start and the end of a six week period. Training load was monitored on a daily basis during this study. External load measures were; total distance covered (TD), total acceleration and deceleration distance > 2m.s-2 (A/D Load). Arbitrary high speed running measures were; metres covered and time spent > 17 km.h-1 (m>HSD, t>HSD) and 21 km.h-1 (m>VHSD, t>VHSD). Individualised high speed running measures were; metres covered and time spent > MAS km.h-1 (m>MAS, t>MAS) and 30% anaerobic speed reserve (m>30ASR, t>30ASR). In addition, internal load measures were also collected; heart rate exertion (HRE) and rating of perceived exertion (RPE). Linear regression analysis was used to establish the dose-response relationship between mean weekly training load and changes in aerobic fitness. Substantial very large associations were found between t>MAS and changes in aerobic fitness (R2 = 0.59). Substantial large associations were found for t>30ASR (R2 = 0.38) and m>MAS (R2 = 0.25). Unsubstantial associations were found for all other variables. An individualised approach to monitoring training load, in particular t>MAS, may be a more appropriate method than using traditional arbitrary speed thresholds when monitoring the dose-response relationship between training load and changes in aerobic fitness.

#7 Monitoring of Post-match Fatigue in Professional Soccer: Welcome to the Real World
Reference: Sports Med. 2018 May 8. doi: 10.1007/s40279-018-0935-z. [Epub ahead of print]
Authors: Carling C, Lacome M, McCall A, Dupont G, Le Gall F, Simpson B, Buchheit M
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Summary: Participation in soccer match-play leads to acute and transient subjective, biochemical, metabolic and physical disturbances in players over subsequent hours and days. Inadequate time for rest and regeneration between matches can expose players to the risk of training and competing whilst not entirely recovered. In professional soccer, contemporary competitive schedules can require teams to compete in excess of 60 matches over the course of the season with periods of fixture congestion occurring, prompting much attention from researchers and practitioners to the monitoring of fatigue and readiness to play. A comprehensive body of research has investigated post-match acute and residual fatigue responses. Yet the relevance of the research for professional soccer contexts is debatable, notably in relation to the study populations and designs employed. Monitoring can indeed be invasive, expensive, time inefficient, and difficult to perform routinely and simultaneously in a large squad of regularly competing players. Uncertainty also exists regarding the meaningfulness and interpretation of changes in fatigue response values and their functional relevance, and practical applicability in the field. The real-world need and cost-benefit of monitoring must be carefully weighed up. In relation to professional soccer contexts, this opinion paper intends to (1) debate the need for post-match fatigue monitoring; (2) critique the real-world relevance of the current research literature; (3) discuss the practical burden relating to measurement tools and protocols, and the collection, interpretation and application of data in the field; and (4) propose future research perspectives.

#8 Comparison of technical and physical activities between 8 vs. 8 and 11 vs. 11 games in young Korean soccer players
Reference: J Exerc Rehabil. 2018 Apr 26;14(2):253-258. doi: 10.12965/jer.1836034.017. eCollection 2018 Apr.
Authors: Oh SH, Joo CH
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Summary: The aims of this study were to examine the differences in technical aspects and physical demands between small-size games (SSG; 8 vs. 8) and regular-size games (RSG; 11 vs. 11) in young Korean soccer players. Seventy-nine young soccer players from 6 teams (U-12) volunteered to participate in the study. The players completed 4 games (2 SSG, 62×51 m, and 2 RSG, 80×54 m) in 2 days. Each game was filmed to evaluate technical actions. Physical demand variables were measured using global positioning system technology. SSG showed significantly greater numbers of technical plays among 17 variables when compared to RSG (P<0.05). The players covered significantly greater total distance during low-, moderate-, and high-speed running and sprinting in SSG than in RSG (P<0.05). Higher numbers of high-intensity activities (repeated high-intensity efforts, explosive efforts, decelera-tions, accelerations, and sprinting) were observed in SSG compared to RSG (P<0.05). Mean heart rate was also higher in SSG than in RSG (P<0.05). Despite the greater physical demands during SSG, the exercise intensity was similar to that reported in previous studies. Therefore, the SSG format applied in the present study can be a suitable official game format for Korean young soccer players, resulting in significantly greater exposure to technical plays without excessive physical demands.

#9 Hamstring and Ankle Flexibility Deficits Are Weak Risk Factors for Hamstring Injury in Professional Soccer Players: A Prospective Cohort Study of 438 Players Including 78 Injuries
Reference: Am J Sports Med. 2018 May 1:363546518773057. doi: 10.1177/0363546518773057. [Epub ahead of print]
Authors: van Dyk N, Farooq A, Bahr R, Witvrouw E
Summary: Hamstring injuries remain a significant injury burden in sports such as soccer that involve high-speed running. It has repeatedly been identified as the most common noncontact injury in elite male soccer, representing 12% of all injuries. As the incidence of hamstring injuries remains high, investigations are aimed at better understanding how to prevent hamstring injuries. Stretching to improve flexibility is commonly used in elite-level sports, but risk factor studies have reported contradicting results, leading to unclear conclusions regarding flexibility as a risk factor for hamstring injuries. The purpose was to investigate the association of lower limb flexibility with the risk of hamstring injuries in professional soccer players. All teams (n = 18) eligible to compete in the premier soccer league in Qatar (Qatar Stars League [QSL]) underwent a comprehensive musculoskeletal assessment during their annual periodic health evaluation at Aspetar Orthopaedic and Sports Medicine Hospital in Doha, Qatar. Variables included passive knee extension and ankle dorsiflexion range of motion. A clustered multivariate Cox regression analysis was used to identify associations with the risk of hamstring injuries. Receiver operating characteristic (ROC) curves were calculated to determine sensitivity and specificity. A total of 438 unique players (72.4% of all QSL players) competed for 601 player-seasons (148 players competed both seasons) and sustained 78 hamstring injuries. Passive knee extension range of motion (hazard ratio [HR], 0.97 [95% CI, 0.95-0.99]; P = .008) and ankle dorsiflexion range of motion (HR, 0.93 [95% CI, 0.88-0.99]; P = .02) were independently associated with the injury risk. The absolute differences between the injured and uninjured players were 1.8° and 1.4 cm, respectively, with small effect sizes ( d < 0.2). The ROC curve analyses showed an area under the curve of 0.52 for passive knee extension and 0.61 for ankle dorsiflexion, indicating failed to poor combined sensitivity and specificity of the 2 strength variables identified in the multivariate Cox regression analysis. This study identified deficits in passive hamstring and ankle dorsiflexion range of motion as weak risk factors for a hamstring injury. These findings have little clinical value in predicting the risk of future hamstring injuries, and test results must therefore be interpreted cautiously in athletic screening.

#10 Maturity Status Strongly Influences the Relative Age Effect in International Elite Under-9 Soccer
Reference: J Sports Sci Med. 2018 May 14;17(2):216-222. eCollection 2018 Jun.
Authors: Muller L, Gehmaier J, Gonaus C, Raschner C, Muller E
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Summary: The aim of the study was to assess the role of the relative age effect (RAE) and to investigate the influence of the biological maturity status on the RAE in international under-9 soccer. The birth dates of 222 male participants of the U9 Eurochampionship Soccer Tournament in Vienna in 2016 were analyzed and divided into four relative age quarters (Q1-Q4) and the biological maturity status was assessed with the age at peak height velocity (APHV) method. Based on the mean±standard deviation of the APHV, the athletes were divided into three groups of maturity: early, normal and late maturing. Chi-Square-tests were used to assess the difference between the observed and the expected even relative age quarter distribution and to evaluate the difference between the observed distribution of early, normal and late maturing athletes and the expected normal distribution. A univariate analysis of variance was performed to assess differences in the APHV between the relative age quarters. A RAE was present (χ2 = 23.87; p < 0.001; ω = 0.33). A significant difference was found in APHV between the four relative age quarters (F = 9.906; p < 0.001); relatively older athletes were significantly less mature. A significant difference was found between the distribution of early, normal and late maturing athletes and the expected normal distribution for athletes of Q1 (high percentage of late maturing athletes: 27%; χ2 = 17.69; p < 0.001; ω = 0.46) and of Q4 (high percentage of early maturing soccer players: 31%; χ2 = 12.08; p = 0.002; ω = 0.58). These findings demonstrated that the selection process in international soccer, with athletes younger than 9 years, seems to be associated with the biological maturity status and the relative age. Relatively younger soccer players seem to have a better chance for selection for international tournaments, if they enter puberty at an earlier age, whereas relatively older athletes seem to have an increased likelihood for selection independent of their biological maturity status.

#11 Relation Between Iliopsoas Cross-sectional Area and Kicked Ball Speed in Soccer Players
Reference: Int J Sports Med. 2018 May 14. doi: 10.1055/a-0592-7370. [Epub ahead of print]
Authors: Wakahara T, Chiba M
Summary: This study aimed to investigate the relationship between the maximal anatomical cross-sectional area (ACSA) of the iliopsoas muscle and ball speed in side-foot and instep kicks. The ACSA of the psoas major and iliacus was measured in 29 male collegiate soccer players by using magnetic resonance imaging. They performed maximal side-foot and instep kicks to a stationary ball. The kicked ball speed was measured with a high-speed camera. Ball speed in the side-foot and instep kicks was significantly correlated with body height (side-foot kick: r=0.650, P<0.001; instep kick: r=0.583, P<0.001). After adjustment for body height, the maximal ACSA of the psoas major was significantly correlated with ball speed in the side-foot kick (r=0.441, P=0.017), but not in the instep kick. The maximal ACSA of the iliacus was not correlated with ball speed in side-foot or instep kicks, even after adjustment for body height. Our results suggest that: 1) body height is a significant determinant of the ball speed in side-foot and instep kicks, and 2) for a given body height, the maximal ACSA of the dominant psoas major is a factor that affects the ball speed in side-foot kick.

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