Latest research in football - week 41 - 2015

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 Comparative Study of Bronchial Hyperresponsiveness Between Football and Judo Groups in Prepubertal Boys
Reference: Asian J Sports Med. 2015 Jun;6(2):e24043. doi: 10.5812/asjsm.6(2)2015.24043. Epub 2015 Jun 20.
Authors: Triki M, Rebai H, Aouichaoui C, Shamssain M, Masmoudi K, Fellmann N, Zouari H, Zouari N, Tabka Z
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Summary: Exercise induced bronchospasm (EIB) commonly occurs during exercise. The comparative effects of different sports on airway responsiveness among prepubertal boys remain to be determined. To assess differences in post exercise spirometry between footballers, judokas and a control group in prepubertal boys. A total of ninety six prepubertal boys were studied. Bronchial hyper responsiveness (BHR) to exercise challenge test was defined by a diagnosis of baseline spirometry, followed by an incremental exercise test. To date, the best test to confirm EIB may simply be standard pulmonary function testing before and after high-intensity exercise. A 10% or greater post-challenge fall in forced expiratory volume in FEV1 is used as a diagnostic criterion. There was no significant difference in baseline spirometry between all groups (P > 0.05). The post exercise spirometry test revealed the presence of EIB in 16 of 32 (50%) footballers against 9 out of 32 (28.12%) in both judokas and control subjects at 5 min after the exercise. Also, there was a significantly higher decrease (P < 0.05) in mean FEV1 at 5 minuts in footballers (-9.60 ± 6.18) compared to judokas (-5.41 ± 5.85). The footballers have more BHR than judokas, especially at 5min after the exercise. This may be due to prolonged hyperventilation, atopy and increased exposure to inhaled allergens and pollutants during training and competition.

#2 T-lymphocyte populations following a period of high volume training in female soccer players
Reference: Physiol Behav. 2015 Sep 30;152(Pt A):175-181. doi: 10.1016/j.physbeh.2015.09.027. [Epub ahead of print]
Authors: Brown FF, Bigley AB, Ross JC, LaVoy EC, Simpson RJ, Galloway SD
Summary: The purpose of the study was to investigate the T-lymphocyte response to a period of increased training volume in trained females compared to habitual activity in female controls. Thirteen trained female (19.8±1.9yrs) soccer players were monitored during a two-week long high volume training period (increased by 39%) and thirteen female untrained (20.5±2.2yrs) controls were monitored during two-weeks of habitual activity. Blood lymphocytes, collected at rest, were isolated before and after the two-week period. Isolated lymphocytes were assessed for the cell surface expression of the co-receptor CD28, a marker of T-lymphocyte naivety, and CD57 a marker used to identify highly-differentiated T-lymphocytes. Co-expression of these markers was identified on helper CD4+ and cytotoxic CD8+ T-lymphocytes. In addition a further population of γδ+ T-lymphocytes were identified. Plasma was used to determine Cytomegalovirus (CMV) serostatus. No difference was observed in the T-lymphocyte populations following the two-week period of increased volume training. At baseline the number of total CD3+, cytotoxic CD8+, naïve (CD8+ CD28+ CD57-), intermediate (CD8+ CD28+ CD57+) T-lymphocytes and the number and proportion of γδ+ T-lymphocytes were greater in the trained compared to the untrained females (p<0.05). The proportion of CD4+T-lymphocytes was greater in the untrained compared to the trained (p<0.05), in turn the CD4+:CD8+ ratio was also greater in the untrained females (p<0.05). Inclusion of percentage body fat as a covariate removed the main effect of training status in all T-lymphocyte sub-populations, with the exception of the γδ+ T-lymphocyte population. 8% of the untrained group was defined as positive for CMV whereas 23% of the trained group was positive for CMV. However, CMV was not a significant covariate in the analysis of T-lymphocyte proportions. The period of high volume training had no effect on T-lymphocyte populations in trained females. However, baseline training status differences were evident between groups. This indicates that long-term exercise training, as opposed to short-term changes in exercise volume, appears to elicit discernible changes in the composition of the blood T-lymphocyte pool.

#3 Assessment of Energy Intake and Energy Expenditure of Male Adolescent Academy-Level Soccer Players during a Competitive Week
Reference: Nutrients. 2015 Oct 2;7(10):8392-401. doi: 10.3390/nu7105400.
Authors: Briggs MA, Cockburn E, Rumbold PL, Rae G, Stevenson EJ, Russell M
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Summary: This study investigated the energy intake and expenditure of professional adolescent academy-level soccer players during a competitive week. Over a seven day period that included four training days, two rest days and a match day, energy intake (self-reported weighed food diary and 24-h recall) and expenditure (tri-axial accelerometry) were recorded in 10 male players from a professional English Premier League club. The mean macronutrient composition of the dietary intake was 318 ± 24 g·day(-1) (5.6 ± 0.4 g·kg(-1) BM) carbohydrate, 86 ± 10 g·day(-1) (1.5 ± 0.2 g·kg(-1) BM) protein and 70 ± 7 g·day(-1) (1.2 ± 0.1 g·kg(-1) BM) fats, representing 55% ± 3%, 16% ± 1%, and 29% ± 2% of mean daily energy intake respectively. A mean daily energy deficit of -1302 ± 1662 kJ (p = 0.035) was observed between energy intake (9395 ± 1344 kJ) and energy expenditure (10679 ± 1026 kJ). Match days (-2278 ± 2307 kJ, p = 0.012) and heavy training days (-2114 ± 2257 kJ, p = 0.016) elicited the greatest deficits between intake and expenditure. In conclusion, the mean daily energy intake of professional adolescent academy-level soccer players was lower than the energy expended during a competitive week. The magnitudes of these deficits were greatest on match and heavy training days. These findings may have both short and long term implications on the performance and physical development of adolescent soccer players.

#4 Sports injuries profile of a first division Brazilian soccer team: a descriptive cohort study
Reference: Braz J Phys Ther. 2015 Oct 6. pii: S1413-35552015005040120. [Epub ahead of print]
Authors: Reis GF, Santos TR, Lasmar RC, Oliveira Júnior O, Lopes RF, Fonseca ST
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Summary: The purpose of the study was to establish the injury profile of soccer players from a first division Brazilian soccer team. In addition, we investigated the association between the characteristics of the injuries and the player's age and position. Forty-eight players from a Brazilian first division soccer team were followed during one season. Descriptive statistics were used to characterize the injury profile. Spearman's tests were used to verify the association between the number and severity of injuries and the player's age. Chi-square test was used to verify the association between type of injury and player's position. Fisher's exact test was used to verify the association between the severity of injuries and player's position. The incidence of injuries was 42.84/1000 hours in matches and 2.40/1000 hours in training. The injury severity was 19.5±34.4 days off competition or training. Lower limb was the most common location of injury and most injuries were muscular/tendinous, overuse, non-recurrent, and non-contact injuries. Player's age correlated with the amount and severity of muscle and tendon injuries. Defenders had more minimal injuries (1-3 days lost), while forwards had more moderate (8-28 days lost) and severe injuries (>28 days lost). Furthermore, wingbacks had more muscle and tendon injuries, while midfielders had more joint and ligament injuries. The injury profile of the Brazilian players investigated in this study reflected regional differences in soccer practices. Results confirm the influence of the player's age and position on the soccer injuries profile.

#5 Visualization of air flow around soccer ball using a particle image velocimetry
Reference: Sci Rep. 2015 Oct 8;5:15108. doi: 10.1038/srep15108.
Authors: Hong S, Asai T, Seo K
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Summary: A traditional soccer ball is constructed using 32 pentagonal and hexagonal panels. In recent years, however, the likes of the Teamgeist and Jabulani balls, constructed from 14 and 8 panels, respectively, have entered the field, marking a significant departure from conventionality in terms of shape and design. Moreover, the recently introduced Brazuca ball features a new 6-panel design and has already been adopted by many soccer leagues. However, the shapes of the constituent panels of these balls differ substantially from those of conventional balls. Therefore, this study set out to investigate the flight and aerodynamic characteristics of different orientations of the soccer ball, which is constructed from panels of different shapes. A wind tunnel test showed substantial differences in the aerodynamic forces acting on the ball, depending on its orientation. Substantial differences were also observed in the aerodynamic forces acting on the ball in different directions, corresponding to its orientation and rotation. Moreover, two-dimensional particle image velocimetry (2D-PIV) measurements showed that the boundary separation varies depending on the orientation of the ball. Based on these results, we can conclude that the shape of the panels of a soccer ball substantially affects its flight trajectory.

#6 Training Load and Player Monitoring in High-Level Football: Current Practice and Perceptions
Reference: Int J Sports Physiol Perform. 2015 Oct 9. [Epub ahead of print]
Authors: Akenhead R, Nassis GP
Summary: Training load (TL) is monitored with the aim of making evidence-based decisions on appropriate loading schemes to reduce injuries and enhance team performance. However little is known in detail about the variables of load and methods analysis used in high level football. Therefore the aim of this study was to provide information on the practices and perceptions of monitoring in professional clubs. Eighty two high-level football clubs from Europe, the United States and Australia were invited to answer questions relating to (1) how TL is quantified; (2) how players' responses are monitored, and (3) their perceptions of the effectiveness of monitoring. Forty one responses were received. All teams used GPS and heart rate monitors during all training sessions and 28 used RPE. The top 5 ranking TL variables were; acceleration (various thresholds), total distance, distance covered above 5.5 m·s-1, estimated metabolic power, and heart rate exertion. Players' responses to training are monitored using questionnaires (68% of clubs) and submaximal exercise protocols (41%). Differences in expected vs. actual effectiveness of monitoring were 23% and 20% for injury prevention and performance enhancement respectively (P<0.001 d=1.0 to 1.4). Of the perceived barriers to effectiveness, "limited human resources" scored highest, followed by "coach buy-in". The discrepancy between expected and actual effectiveness appears to be due to suboptimal integration with coaches, insufficient human resources and concerns over the reliability of assessment tools. Future approaches should critically evaluate the usefulness of current monitoring tools and explore methods of reducing the identified barriers to effectiveness.

#7 The epidemiology of injuries in football at the London 2012 Paralympic Games
Reference: PM R. 2015 Oct 7. pii: S1934-1482(15)01033-3. doi: 10.1016/j.pmrj.2015.09.025. [Epub ahead of print]
Authors: Webborn N, Cushman D, Blauwet CA, Emery C, Derman W, Schwellnus M, Stomphorst J, Van de Vliet P, Willick SE
Summary: The epidemiology of injury in Paralympic football has received little attention. A study of all sports at the London 2012 Paralympic Games identified football 5-a-side as the sport with the highest injury rate, meriting further detailed analysis, which may allow for future preventative strategies. The purpose was to examine the injury rates and risk factors associated with injury in Paralympic football. Secondary analysis of a prospective cohort study of injuries to football 5-a-side and football 7-a-side athletes. London 2012 Paralympic Games PARTICIPANTS: 70 football 5-a-side athletes and 96 football 7-a-side athletes. Athletes from all but one country chose to participate in this study. The Paralympic Injury and Illness Surveillance System was used to track injuries over the Games, with data entered by medical staff. The overall IR for football 5-a-side was 22.4 injuries /1000 athlete-days (95% CI; 14.1-33.8) with an IP of 31.4 injuries per 100 athletes (95% CI; 20.9-43.6). In 5-a-side competition, 62.5% of injuries were associated with foul play. The overall IR for football 7-a-side was 10.4 injuries/1000 athlete-days (95% CI; 5.4-15.5), with an IP of 14.6 injuries per 100 athletes (95% CI; 7.5-21.6). The most commonly injured body region in both sports was the lower extremity. To our knowledge, this is the first study examining IR and risk factors associated with injury in Paralympic football. Future studies are needed to determine mechanisms of injury and independent risk factors for injury, thus informing prevention strategies.

#8 Effects of strength training on squat and sprint performance in soccer players
Reference: J Strength Cond Res. 2015 Oct 13. [Epub ahead of print]
Authors: Styles WJ, Matthews MJ, Comfort P
Summary: Researchers have demonstrated that increases in strength result in increases in athletic performance, although the development of strength is still neglected in some sports. Our aim was to determine whether a simple in-season strength training program would result in increases in maximal squat strength and short sprint performance, in professional soccer players. Professional soccer players (n=17, age = 18.3 ± 1.2 years, height = 1.79 ± 0.06 m, body mass (BM) = 75.5 ± 6.1 kg) completed one repetition maximum (1RM) back squat and sprint tests (5-, 10-, 20 m) before and after a six-week (2 x week) in-season strength training (85-90% 1RM) intervention. Strength training resulted in significant improvements in absolute and relative strength (pre: 125.4 ± 13.8 kg, post 149.3 ± 16.2 kg, p < 0.001, Cohen's d = 0.62; 1RM/BM pre: 1.66 ± 0.24, post 1.96 ± 0.29, p < 0.001, Cohen's d = 0.45; respectively). Similarly, there were small yet significant improvements in sprint performance over 5 m (pre 1.11 ± 0.04 s, post 1.05 ± 0.05 s, p < 0.001, Cohen's d = 0.55) 10 m (pre 1.83 ± 0.05 s, post 1.78 ± 0.05 s, p < 0.001, Cohen's d = 0.45) and 20 m (pre 3.09 ± 0.07 s, post 3.05 ± 0.05 s, p < 0.001, Cohen's d = 0.31). Changes in maximal squat strength appear to be reflected in improvements in short sprint performance highlighting the importance of developing maximal strength to improve short sprint performance. Moreover this demonstrates that these improvements can be achieved during the competitive season in professional soccer players.

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