Latest research in football - week 21 - 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 The influence of relative age on the composition of professional soccer squads
Authors: Ostapczuk M, Musch J.
Reference: EJSS (Champaign). 2013 May;13(3):249-55. doi: 10.1080/17461391.2011.606841. Epub 2011 Nov 1.
Summary: Abstract Children born shortly after the cut-off date applying for age grouping in minor sports profit from being able to remain for almost an additional year in their respective age group compared to those born later in the same year. A shift of the cut-off date in German youth soccer in 1997 allowed us to investigate the effect of a favourable relative age as well as the effect of a change of the cut-off date on the birth-date distribution of soccer players in the 1st Bundesliga, the highest professional soccer league in Germany. Both the cut-off date and the change of the cut-off date exerted a significant influence on the composition of professional senior squads. In the 1997/98 season, there was an overrepresentation of players profiting from the old cut-off date of 1 August. In the 2007/08 season, 10 years after the change of the cut-off date, there was an overrepresentation of players born shortly after the new cut-off date of 1 January. This pattern of results shows that owing to the cut-off dates applying in youth soccer, the date of birth of young players systematically influences their later professional success and career.

#2 Analysis of entries into the penalty area as a performance indicator in soccer
Authors: Ruiz-Ruiz C, Fradua L, Fernández-García A, Zubillaga A.
Reference: EJSS (Champaign). 2013 May;13(3):241-8. doi: 10.1080/17461391.2011.606834. Epub 2011 Oct 21.
Summary: This study examines entries into the penalty area as a performance indicator that distinguishes between winning, drawing and losing soccer teams. It assesses whether entries into the penalty area are influenced by match status, a player's dismissal and the respective quality of the competing teams. Two observers analysed the relation between defensive and offensive strategies and their scoring consequences for all 64 matches played in the 2006 World Cup. Kappa values ranged between 0.93 and 0.98 for intra-reliability and between 0.88 and 0.98 for inter-reliability. It was found that winning teams received significantly fewer entries into their own penalty area (mean=41.42, s=11.86) than drawing (mean=50.07, s=14.75) and losing teams (mean=47.23, s=12.14). Teams that received more entries into their own penalty area than the opposing team were significantly more likely to concede a goal. Teams losing by one (mean=0.41, s=0.21), two (mean=0.42, s=0.26) or more than two goals (mean=0.34, s=0.13) received significantly fewer entries into the penalty area per minute than teams winning by one (mean=0.55, s=0.27) or two goals (mean=0.59, s=0.39). Teams with fewer players on the pitch received significantly more entries into the penalty area per minute than teams with more (mean=0.22, s=0.07) or the same number (mean=0.14, s=0.05) of players. Based on these results, it is suggested that teams should enter the opposing team's penalty area but should not allow their opponents to do the same. These results also highlight the significance of the dismissal of a player.

#3 Soccer Training Improves Cardiac Function in Men with Type 2 Diabetes
Authors: Friis Schmidt J, Rostgaard Andersen T, Horton J, Brix J, Tarnow L, Krustrup P, Juel Andersen L, Bangsbo J, Riis Hansen P.
Reference: Med Sci Sports Exerc. 2013 May 10. [Epub ahead of print]
Summary: Patients with type 2 diabetes (T2DM) have an increased risk of cardiovascular disease which is worsened by physical inactivity. Subclinical myocardial dysfunction is associated with increased risk of heart failure and impaired prognosis in T2DM; however, it is not clear if exercise training can counteract the early signs of diabetic heart disease. To evaluate the effects of soccer training on cardiac function, exercise capacity and blood pressure in middle-aged men with T2DM. Twenty-one men aged 49.8 (±1.7) yrs with T2DM and no history of cardiovascular disease, participated in a soccer training group (STG; N=12) that trained one h twice a week or a control group (CG; N=9) with no change in lifestyle. Examinations included comprehensive transthoracic echocardiography, measurements of blood pressure, maximal oxygen consumption (VO2max) and intermittent endurance capacity before and after 12 and 24 wks. Two-way repeated-measures ANOVA was applied. After 24 wks of soccer training, left ventricular (LV) end-diastolic diameter and volume were increased significantly compared to baseline. LV longitudinal systolic displacement was augmented significantly by 23% and global longitudinal 2D strain increased significantly by 10%. LV diastolic function, determined by mitral inflow (E/A-ratio) and peak diastolic velocity E´ were increased significantly by 18% and 29%, respectively while LV filling pressure E/E´ was reduced significantly by 15%. Systolic, diastolic and mean arterial pressures were all reduced by 8 mmHg. VO2max and intermittent endurance capacity was 12% and 42% significantly higher, respectively. No changes in any of the measured parameters were observed in CG. Regular soccer training improves cardiac function, increases exercise capacity and lowers blood pressure in men with T2DM.

#4 Effectiveness of ultrasound-guided percutaneous electrolysis intratendon (epi) in the treatment of insertional patellar tendinopathy in soccer players
Authors:  Sánchez-Ibáñez JM, Alves R, Polidori F, Valera F, Minaya F, Valles-Martí S, Baños L.
Reference: Br J Sports Med. 2013 Jun;47(9):e2. doi: 10.1136/bjsports-2013-092459.24.
Summary: Patellar tendinopathy or 'jumper's knee' is considered more of a degenerative (tendinosis) than a non-inflammatory process (tendinitis). Recent histopathological studies have shown the absence of inflammatory cells in this type of pathology and demonstrated the presence of myxoid degeneration, disruption of the collagen fibres and signs of hypoxia in tenocytes and resident macrophages. Percutaneous electrolysis intratendon (EPI) is a non-thermal electrochemical ablation through a cathodic flow in the region or clinical focus of the degenerated tendon. EPI produces the dissociation of water, salts and amino acids of the extracellular matrix creating new molecules through ionic instability. The aim of this research is to prove the effectiveness of EPI in the treatment of patellar tendinopathy and to observe the healing time in 23 football players. A prospective study was performed between January and December 2011 involving 23 patients, all soccer players diagnosed with patellar tendinopathy and referred to the Physiotherapy Service of the Sports Recovery Center, CEREDE, in Barcelona. All 23 patients were male football players. In the total study population the clinical location corresponded to the osteotendinous junction of the lower pole of the patella, leading to the diagnosis of enthesopathy of the proximal patella. Based on the first observation and according to their score on the questionnaire, Victorian Institute of Sport Assessment-Patellar Tendon (VISA-P), we classified the patients into two groups: Group-1 (worse prognosis, N=12) who scored a VISA-P≤50 (52.2%) and Group-2 (better prognosis, N=11) with VISA-P score>50 (47.8%). All patients underwent EPI technique that was applied with an intensity of 3 mA during a period of 4 s, using the approved electro stimulator EPI (Epimedical scp, Barcelona 08017, Spain). The intervention was performed under ultrasound guidance with a portable ultrasound (General Electric LogicE). Regarding the VISA-P score, Group 1 (n=12) in the first examination had a mean VISA-P score of 33.67 (SD±12.27, 95% CI 25.87 to 41.6) and in the last observation an average of 83.17 (SD±15.36, 95% CI 73.41 to 92.93), showing a statistically significant improvement in the results of the VISA-P questionnaire. Group 2 (N=11) in the first observation had a mean VISA-P of 68.09 (SD±10.50, 95% CI 61.04 to 75.15) and in the last one, an average of 85.27 (SD±6.15, 95% CI 81.14 to 89.40) with statistically significant differences between the scores of the first and last observation. In Group 1 (N=12), the average healing time was 4.66 weeks (95% CI 3.25 to 6.08) while in the group with the better prognosis (Group 2, N=11) it was 2.18 weeks (95% CI 2.57 to 4.39), both with statistically significant differences. Regarding the estimation of the number of interventions with EPI needed to achieve healing, in the group with the worse prognosis (Group 1; N=12) the average number was 5.0 EPI sessions (95% 3.59 to 6.40) while in the group with better prognosis (Group 2; N=11), the mean number of sessions needed to achieve healing was 2.45 EPI sessions. The ultrasound guided percutaneous electrolysis technique (EPI) has proved to be highly effective in the treatment of proximal patellar enthesopathy in a population of soccer players, with a significant improvement in 91.7% of the total sample (N=22), as measured by the Victorian Institute of Sport Assessment-Patellar Tendon (VISA-P) questionnaire. An analysis of Kaplan-Meier survival allowed us to estimate the time and number of sessions of EPI technique needed to achieve cure for both the group with worse prognosis (Group 1) and for the group with better prognosis (Group 2), independent of the stadium of the patient according to Blazina's Classification. EPI technology has proven to be very effective and therefore should not be a criterion for surgical intervention patients that, at first observation, are in stage III of Blazina's Classification. EPI technology has also proven to be effective in curing insertional patellar tendinopathy in soccer players regardless of duration and evolution of the clinical symptoms.

#5 Mechanical properties of the triceps surae: Differences between football and non-football players
Authors: Faria A, Gabriel R, Abrantes J, Wood P, Moreira H.
Reference: J Sports Sci. 2013 May 15. [Epub ahead of print]
Summary: We investigated the mechanical properties of the triceps surae between professional, junior, and non-football players. Fifty-nine men participated in this study. The mechanical properties of the right legs' triceps surae were measured in vivo using a free oscillation technique; no significant differences existed between the groups. The mean results for musculo-articular stiffness, damping coefficient, and damping ratio were as follows: professional football players (21523 N/m, 330.8 N · s/m, and 0.201); junior football players (21063 N/m, 274.4 N · s/m, and 0.173); and non-players (19457 N/m, 281.5 N · s/m, and 0.184). When analysed according to position, the results were as follows: defender (21447 N/m, 308.6 N · s/m, and 0.189); midfielder (20762 N/m, 250.7 N · s/m, and 0.157); winger (21322 N/m, 335.1 N · s/m, and 0.212); forward (22085 N/m, 416.2 N · s/m, and 0.254); and non-players (19457 N/m, 281.5 N · s/m, and 0.184). Thus, football training, football games, and the position played had no effect on triceps surae mechanical properties. These results may be attributed to opposing adaptations between different types of training that are usually implemented in football. Alternatively, the minimum strain amplitude and/or frequency threshold of the triceps surae required to trigger adaptations of mechanical properties might not be achieved by football players with football training and matches.

#6 Incidence and characteristics of injuries during the 2011 West Africa Football Union (WAFU) Nations' Cup
Authors: Akodu AK, Owoeye OB, Ajenifuja M, Akinbo SR, Olatona F, Ogunkunle O.
Reference: Afr J Med Med Sci. 2012 Dec;41(4):423-8.
Summary: Prospective studies on football injuries and their risk factors in the African setting are sparse. Such studies are needed to understand the peculiarities of injuries and hence proffer appropriate intervention for injury prevention in the region. To evaluate the incidence and characteristics of match injuries during the 2011 West Africa Football Union (WAFU) cup. Team physiotherapists from the participating teams documented all newly incurred injuries on standardised injury report forms using the Federation of International Football Association's (FIFA) Medical Assessment and Research Centre protocols. An overall of 89 injuries were sustained during the tournament, resulting in 9.9 injuries per match or 289 injuries per 1000 player hours. Seventeen (19.1%) of these injuries resulted in loss of competition activity (time-loss), equivalent to 1.9 injuries per match or 55.2 injuries per 1000 player hours. Over three quarters (73; 82%) of injuries were incurred through contact with another player. The lower leg accounted for almost a quarter of all injuries (21; 23.6%) while the knee recorded the highest number of time-loss injuries (5; 29.4%). The most frequent types of injury were contusion (61; 68.5%) and strain (13; 14.6%). The overall incidence of injuries during the WAFU cup was much higher than those of other tournaments ever documented but the characteristics of injuries were similar. In order to fully define the nature of injuries and more reliably identify the risk of injury for the establishment of injury prevention strategies that will be appropriate for this region of the world, it is imperative that further systematic injury recording and analysis in African players are carried out.

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