Latest research in football - week 20 - 2013

Latest research of the week

As previous literature updates, we have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.


Following studies were retrieved for this week:

#1 Interpreting Physical Performance in Professional Soccer Match-Play: Should We be More Pragmatic in Our Approach?
Author: Carling C.
Reference: Sports Med. 2013 May 11. [Epub ahead of print]
Summary: Academic and practitioner interest in the physical performance of male professional soccer players in the competition setting determined via time-motion analyses has grown substantially over the last four decades leading to a substantial body of published research and aiding development of a more systematic evidence-based framework for physical conditioning. Findings have forcibly shaped contemporary opinions in the sport with researchers and practitioners frequently emphasising the important role that physical performance plays in match outcomes. Time-motion analyses have also influenced practice as player conditioning programmes can be tailored according to the different physical demands identified across individual playing positions. Yet despite a more systematic approach to physical conditioning, data indicate that even at the very highest standards of competition, the contemporary player is still susceptible to transient and end-game fatigue. Over the course of this article, the author suggests that a more pragmatic approach to interpreting the current body of time-motion analysis data and its application in the practical setting is nevertheless required. Examples of this are addressed using findings in the literature to examine (a) the association between competitive physical performance and 'success' in professional soccer, (b) current approaches to interpreting differences in time-motion analysis data across playing positions, and (c) whether data can realistically be used to demonstrate the occurrence of fatigue in match-play. Gaps in the current literature and directions for future research are also identified.

#2 Neuromuscular function, hormonal and redox status and muscle damage of professional soccer players after a high-level competitive match
Authors: Silva JR, Ascensão A, Marques F, Seabra A, Rebelo A, Magalhães J.
Reference: Eur J Appl Physiol. 2013 May 10. [Epub ahead of print]
Summary: The main aim was to analyse the impact of an official match on hormonal and redox status, muscle damage and inflammation and neuromuscular function. Seven high-level male soccer players from the same team performed an official match and data were collected 72 h before, 24, 48 and 72 h post-match. Plasma testosterone/cortisol ratio (T/C), creatine kinase (CK), superoxide dismutase (SOD), glutathione peroxidase (GPX) and reductase (GR) activities, myoglobin (Mb), C-reactive protein (CRP), uric acid (UA), protein sulfhydryls (-SH), malondialdehyde (MDA) concentrations and total antioxidant status (TAS) were measured. Sprint, jump and change of direction performance, and maximal isokinetic knee extension and flexion were obtained as neuromuscular functional parameters. Cortisol increased and T/C decreased until 48 h recovery (P < 0.05). Mb, CRP and -SH (P < 0.05) increased at 24 h and CK, TAS, SOD and MDA (P < 0.05) increased up to 48 h recovery. GR increased and GPX decreased at 24 h recovery (P < 0.05). Jump performance decreased 24 h post-match (P < 0.05), but no significant alterations in sprint, change of direction and muscle strength were observed. In conclusion, an official match resulted in changes in plasma biomarkers until 48 h of recovery period, without major impact on performance.

#3 World soccer cup as a trigger of cardiovascular events
Authors: Borges DG, Monteiro RA, Schmidt A, Pazin-Filho A.
Reference: Arq Bras Cardiol. 2013 May 14. pii: S0066-782X2013005000035. [Epub ahead of print]
Summary: Acute coronary syndromes are the major cause of death in Brazil and in the world. External stimuli, known also as triggers, such as emotional state and activity, may generate physiopathological changes that can trigger acute coronary syndromes. Among the studied triggers, the impact of stressful events, such as soccer championships, are controversial in literature and there is no effective data on the Brazilian population. To evaluate the acute effects of environmental stress induced by soccer games of the World Soccer Cup on increased incidence of cardiovascular diseases in Brazil. Public data were obtained from the Unified Health System (Sistema Único de Saúde), regarding hospital admissions that had the International Code Disease of acute coronary syndromes from May to August, in 1998, 2002, 2006 and 2010 (155,992 admissions). Analysis was restricted to patients older than 35 years and admitted by clinical specialties. The incidence of myocardial infarction, angina and mortality were compared among days without World Cup soccer games (Group I: 144,166; 61.7 ± 12.3; 59.4% males); on days when there were no Brazil's soccer team matches (Group II: 9,768; 61.8±12.3; 60.0% males); and days when there were Brazil's soccer team matches (Group III; 2,058; 61.6±12.6; 57.8% males). Logistic regression was used to adjust to age, gender, population density and number of medical assistance units. The incidence of myocardial infarction increased during the period of World Cup soccer games (1.09; 95%CI = 1.05-1.15) and days when there were Brazil's matches (1.16; 95%CI = 1.06-1.27). There was no impact on mortality during the Cup (1.00; CI95% = 0.93-1.08) and Brazil's matches (1.04; 95%CI = 0.93-1.22). World Cup soccer games and, specially, Brazil's matches have an impact on the incidence of myocardial infarction, but not on in-hospital mortality.

#4 Reliability and stability of anthropometric and performance measures in highly-trained young soccer players: effect of age and maturation
Authors: Buchheit M, Mendez-Villanueva A.
Reference: J Sports Sci. 2013 May 8. [Epub ahead of print]
Summary: The purpose of this study was to assess both short-term reliability and long-term stability of anthropometric and physical performance measures in highly-trained young soccer players in relation to age and maturation. Data were collected on 80 players from an academy (U13-U18, pre- (n = 14), circum- (n = 32) and post- (n = 34) estimated peak height velocity, PHV). For the reliability analysis, anthropometric and performance tests were repeated twice within a month. For the stability analysis, these tests were repeated 12 times over a 4-year period in 10 players. Absolute reliability was assessed with the typical error of measurement, expressed as a coefficient of variation (CV). Relative reliability and long-term stability were assessed using the intraclass correlation coefficient (ICC). There was no clear age or maturation effect on either the CVs or ICCs: e.g., Post-PHV vs. Pre-PHV: effect size = -0.37 (90% confidence limits (CL):-1.6;0.9), with chances of greater/similar/lower values of 20/20/60%. For the long-term stability analysis, ICCs varied from 0.66 (0.50;0.80) to 0.96 (0.93;0.98) for 10-m sprint time and body mass, respectively. The short-term reliability of anthropometry and physical performance measures is unlikely to be affected by age or maturation. However, some of these measures are unstable throughout adolescence, which questions their usefulness in a talent identification perspective.

#5 Incidence of decreased hip range of motion in youth soccer players and response to a stretching program: a randomized clinical trial
Authors: de Castro JV, Machado KC, Scaramussa K, Gomes J LE.
Reference: J Sport Rehabil. 2013 May;22(2):100-7.
Summary: After years of focusing on the management of anterior cruciate ligament (ACL) injuries, the most common soccer-related injuries, the orthopedic community has concluded that soccer players have a wide range of variation in joint biomechanics and has thus started to focus research efforts on the morphological factors that might contribute to ACL trauma. One such factor is decreased hip-rotation range of motion (ROM), which may be due to compensatory musculoskeletal changes occurring in response to longstanding soccer practice since childhood. Objective: This study sought to assess decreased hip rotation and the influence of stretching exercises on the behavior of the hip joint in players of the youth soccer categories of a Brazilian soccer team. Design: Randomized clinical trial. Setting: University hospital. Patients: 262 male soccer players. Interventions: Subjects were randomly allocated into 2 groups-control or a stretching program. Main Outcome Measures: Subjects were reassessed after 12 wk. Results: The findings suggest that hip-rotation ROM decreases over the years in soccer players. In the study sample, adherence to a stretching program improved only external hip-rotation ROM in the nondominant limb. Conclusion: Playing soccer can restrict rotation ROM of the hip, and adherence to stretching exercises may decrease the harmful effects on the hip joints.

#6 Evolution of World Cup soccer final games 1966-2010: Game structure, speed and play patterns
Authors: Wallace JL, Norton KI.
Reference: J Sci Med Sport. 2013 May 2. pii: S1440-2440(13)00083-2. doi: 10.1016/j.jsams.2013.03.016.
Summary: There are relatively few performance analysis studies on field sports investigating how they evolve from a structural or tactical viewpoint. Field sports like soccer involve complex, non-linear dynamical systems yet consistent patterns of play are recognisable over time and among different sports. This study on soccer trends helps build a framework of potential causative mechanisms for these patterns. Broadcast footage of World Cup finals between 1966 and 2010 was used to assess patterns of play and stop periods, type and duration of game stoppages, ball speed, player density (congestion) and passing rates. This involved computer-based ball tracking and other notational analyses. These results were analysed using linear regression to track changes across time. Almost every variable assessed changed significantly over time. Play duration decreased while stoppage duration increased, both affecting the work: recovery ratios. Ball (game) speed increased by 15% over the 44-year period. Play structure changed towards a higher player density with a 35% greater passing rate. Increases in soccer ball speed and player density show similarities with other field sports and suggest common evolutionary pressures may be driving play structures. The increased intensity of play is paralleled by longer stoppage breaks which allow greater player recovery and subsequently more intense play. Defensive strategies dominate over time as demonstrated by increased player density and congestion. The long-term pattern formations demonstrate successful coordinated states within team structures are predictable and may have universal causative mechanisms.

#7 Illness and Injuries in Elite Football Players-A Prospective Cohort Study During the FIFA Confederations Cup 2009
References: Clin J Sport Med. 2013 May 6. [Epub ahead of print]
Authors: Theron N, Schwellnus M, Derman W, Dvorak J.
Summary: The incidence of injury during elite-level football tournaments has been well documented, but the incidence of illness and medical conditions has not been well studied. The main objective was to analyze the incidence and nature of medical illnesses and injuries in football players. DESIGN:: Prospective cohort study. One hundred eighty-four soccer players (8 teams of 23 players). Incidence (per 1000 player days) of illnesses and injuries. Each team physician was requested to complete a daily report of injury (match and training) and medical illness of their players during the tournament (2070 player days). A total of 63 daily reports were obtained (70% response rate). A total of 56 injuries and 35 illness incidents were recorded, resulting in an overall rate of 16.9 illnesses per 1000 player days and 27.0 injuries (match and training) per 1000 player days. The overall injury rate was 64.4 per 1000 match hours or 2.1 per match. About 0.88 days were lost per injury, and 0.46 days were lost per illness. Thirteen (37%) illnesses were because of conditions of the ear, nose, and throat, and 7 (20%) illnesses were because of other respiratory tract symptoms. The lower limb was the most commonly injured body part, with thigh (20%) being the most frequent location, and contusion (44%) the most frequent type of injury. Illnesses are as common but less severe compared with match and training injuries during an international football tournament. Illnesses comprise an important component in the day-to-day medical care of a traveling football team. Medical illness therefore needs to be considered by the team physicians when planning for and managing the medical needs of elite football teams.

#8 Return to play after thigh muscle injury in elite football players: implementation and validation of the Munich muscle injury classification
Authors: Ekstrand J, Askling C, Magnusson H, Mithoefer K.
Reference: Br J Sports Med. 2013 May 5. [Epub ahead of print]
Summary: To prospectively implement and validate a novel muscle injury classification and to evaluate its predictive value for return to professional football. The recently described Munich muscle injury classification was prospectively evaluated in 31 European professional male football teams during the 2011/2012 season. Thigh muscle injury types were recorded by team medical staff and correlated to individual player exposure and resultant time-loss. In total, 393 thigh muscle injuries occurred. The muscle classification system was well received with a 100% response rate. Two-thirds of thigh muscle injuries were classified as structural and were associated with longer lay-off times compared to functional muscle disorders (p<0.001). Significant differences were observed between structural injury subgroups (minor partial, moderate partial and complete injuries) with increasing lay-off time associated with more severe structural injury. Median lay-off time of functional disorders was 5-8 days without significant differences between subgroups. There was no significant difference in the absence time between anterior and posterior thigh injuries. The Munich muscle classification demonstrates a positive prognostic validity for return to play after thigh muscle injury in professional male football players. Structural injuries are associated with longer average lay-off times than functional muscle disorders. Subclassification of structural injuries correlates with return to play, while subgrouping of functional disorders shows less prognostic relevance. Functional disorders are often underestimated clinically and require further systematic study.

#9 Injuries affect team performance negatively in professional football: an 11-year follow-up of the UEFA Champions League injury study
Authors: Hägglund M, Waldén M, Magnusson H, Kristenson K, Bengtsson H, Ekstrand J.
Reference: Br J Sports Med. 2013 May 3. [Epub ahead of print]
Summary: The influence of injuries on team performance in football has only been scarcely investigated. To study the association between injury rates and team performance in the domestic league play, and in European cups, in male professional football. 24 football teams from nine European countries were followed prospectively for 11 seasons (2001-2012), including 155 team-seasons. Individual training and match exposure and time-loss injuries were registered. To analyse the effect of injury rates on performance, a Generalised Estimating Equation was used to fit a linear regression on team-level data. Each team's season injury rate and performance were evaluated using its own preceding season data for comparison in the analyses. 7792 injuries were reported during 1 026 104 exposure hours. The total injury incidence was 7.7 injuries/1000 h, injury burden 130 injury days lost/1000 h and player match availability 86%. Lower injury burden (p=0.011) and higher match availability (p=0.031) were associated with higher final league ranking. Similarly, lower injury incidence (p=0.035), lower injury burden (p<0.001) and higher match availability (p<0.001) were associated with increased points per league match. Finally, lower injury burden (p=0.043) and higher match availability (p=0.048) were associated with an increase in the Union of European Football Association (UEFA) Season Club Coefficient, reflecting success in the UEFA Champions League or Europa League. Injuries had a significant influence on performance in the league play and in European cups in male professional football. The findings stress the importance of injury prevention to increase a team's chances of success.


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