Latest research in football - week 29 - 2013

#1 Relationship between field performance in high-level soccer players
Authors: Ingebrigtsen J, Brochmann M, Castagna C, Bradley P, Ade J, Krustrup P, Holtermann A.
Reference: J Strength Cond Res. 2013 Jul 8. [Epub ahead of print]
Summary: In order to reduce athlete testing time, the aim of this study was to investigate the relationship between the Yo-Yo intermittent recovery test level 1 (IR1) and 2 (IR2) test performances, maximal sprinting speed (10, 20 and 35 m), repeated sprint ability (RSA) (7x35 m), and sub-maximal heart rates after two and four minutes of the Yo-Yo IR tests by testing 57 high-level soccer players. All players played regularly in one of the three highest levels of Norwegian soccer and were tested during three sessions on three consecutive days. Large correlations were observed between Yo-Yo IR1 and IR2 test performances (r=0.753 p≤0.05). Small and moderate correlations were found between 20 and 35 m sprinting speed and Yo-Yo IR1 performance (r=-0.289 and -0.321, respectively, p≤0.05), while 35 m sprinting speed correlated moderately to Yo-Yo IR2 performance (r=-0.371, p≤0.05). RSA at 10, 20 and 35 m all showed moderate to large correlations to Yo-Yo IR1 performance (r=-0.337 to -0.573, p≤0.05). RSA at 20 m (r = -0.348, p≤0.05) and 35 m (r=-0.552, p≤0.01) correlated moderately and largely to Yo-Yo IR2 performance. Also, moderate and large correlations were found between sub-maximal Yo-Yo IR1 heart rates after 2 (r=-0.483, p≤0.01) and 4 min (r=-0.655, p≤0.01) and Yo-Yo IR1 performance, and 2 min Yo-Yo IR2 heart rate and Yo-Yo IR2 performance (r=-0.530, p≤0.01). ICC measures of sub-maximal HR after 2 and 4 min of Yo-Yo IR1 test, and after 2 min of the Yo-Yo IR2 were 0.92 (CV=4.1%, n=33), 0.93 (CV=3.8%, n=33) and 0.72 (CV=2.9%, n=10). Adjusted ordinary least square (OLS) regressions revealed associations (p≤0.05) between sprint speed at 20 m and 35 m and Yo-Yo IR1 test performance, but only between 35 m and IR2 test performance (p≤0.05). Further, OLS showed that RSA at 35 m was related to both levels of the Yo-Yo IR test (p≤0.01), and that sub-maximal heart rates after 2 and 4 min were independently associated to Yo-Yo IR1 and IR2 performances (p≤0.01). In conclusion, Yo-Yo IR1 and 2 test performances, as well as sprint and RSA performances, correlated very largely, and it may therefore be considered using only one of the Yo-Yo tests and a RSA test, in a general soccer-specific field test protocol. The sub-maximal heart rate measures during Yo-Yo tests are reproducible and may be utilized for frequent, time-efficient and non-exhaustive testing of intermittent exercise capacity of high-level soccer players.


#2 Relative age effect and soccer refereeing: A 'Strategic Adaptation' of relatively younger children?
Authors: Delorme N, Radel R, Raspaud M.
Reference: Eur J Sport Sci. 2013 Jul;13(4):400-6. doi: 10.1080/17461391.2011.635703. Epub 2011 Dec 5.
Summary: Previous research suggested that the relative age effect (RAE) has a psychological influence on children and their decision to engage in a particular sport. Relatively younger children seem to have lower self-esteem. Indeed, because of the disadvantages of being younger, it is assumed that these players experience more situations of failure and inferiority. Because of these negative performance cues, it is likely that these young players feel less competent, which eventually leads to a higher dropout rate. These children can also decide to participate in sports in which physical attributes are less important. This shift from one sport to another can be interpreted as a 'strategic adaptation'. The purpose of this study was thus to investigate whether refereeing could be another form of 'strategic adaptation'. If a child chooses a specific sport but then does not feel competent enough to be a player, refereeing might be an alternate path followed to stay in the environment of a sport they like. Given the minimal age limits for refereeing, two hypotheses were formulated: (1) 'reversed' RAE would be observed in district referees younger than 18 years old and (2) no RAE would be observed in district referees older than 18 years old, regional referees and national referees. The birthdates of all official male soccer referees (n=13,952) were collected from the federation database. Results show that the distribution of all district referees was significantly unbalanced (χ(2)=18.73, df=3, P<0.001) with an over-representation of individuals who were born in the second half of the competitive year. As expected, this imbalance was exclusively located in district referees of 18 years old and less (χ(2)=8.03, df=3, P<0.05), while the distribution was uniform for adults (χ(2)=5.17, df=3, P<0.16). Concerning regional referees (χ(2)=2.09, df=3, P<0.554) and national referees (χ(2)=3.75, df=3, P<0.290), the results also provide support for our initial hypothesis as uniform distributions were found for both groups. This study brings to light new elements in the potential relationship between relative age and refereeing. Qualitative and/or longitudinal research is needed to confirm our quantitative data.


#3 Relative age effects in Swiss junior soccer and their relationship with playing position
Authors: Romann M, Fuchslocher J.
References: Eur J Sport Sci. 2013 Jul;13(4):356-63. doi: 10.1080/17461391.2011.635699. Epub 2011 Dec Summary: Relative age effects (RAEs) refer to age differences between children in the same selection year. The present study investigated the prevalence of RAEs and their link to playing positions in Swiss junior soccer. Swiss male junior soccer players (n=50,581) representing 11% of the age-matched population - members of extra-curricular soccer teams - were evaluated to determine the influence of RAEs on Swiss junior soccer. Subgroups were the national talent development programme (n=2880), and U-15 to U-21 national teams (n=630). While no RAEs were found for the self-selected extra-curricular soccer teams or for the U-20 teams (P>0.05), significant RAEs were found for talent development and the national U-15 to U-19 and U-21 teams (P<0.01). Additionally, defenders born early in the year were significantly overrepresented compared with goalkeepers, midfielders and strikers (P<0.05). In Switzerland, RAEs apparently have substantial influence on the talent identification process for U-15 to U-18 teams, significantly influencing the selection of players in talent development teams already at an early age, but do not influence self-selected participation in extra-curricular soccer. Additionally, the RAE bias may be a predictor of playing positions in national teams. To minimise RAEs in Swiss soccer, systematic education for all coaches regarding RAEs should be established, in addition to a slotting system with rotating calendar cut-off dates.


#4 Mental rotation performance in soccer players and gymnasts in an object-based mental rotation task
Authors: Jansen P, Lehmann J.
Reference: Adv Cogn Psychol. 2013 Jun 17;9(2):92-8. doi: 10.2478/v10053-008-0135-8. Print 2013.
Summary: In this study, the effect of motor expertise on an object-based mental rotation task was investigated. 60 males and 60 females (40 soccer players, 40 gymnasts, and 40 non-athletes, equivalent males and females in each group) solved a psychometric mental rotation task with both cube and human figures. The results revealed that all participants had a higher mental rotation accuracy for human figures compared to cubed figures, that the gender difference was reduced with human figures, and that gymnasts demonstrated a better mental rotation performance than non-athletes. The results are discussed against the background of the existing literature on motor experts, mental rotation performance as well as the importance of the testing situation and the test construction.


#5 A psychometric evaluation of the Group Environment Questionnaire in a sample of professional basketball and soccer players
Authors: Steca P, Pala AN, Greco A, Monzani D, D'Addario M.
Reference: Percept Mot Skills. 2013 Feb;116(1):262-71.
Summary: Psychometric properties of the Group Environment Questionnaire were investigated in a large sample of soccer (n = 222) and professional basketball players (n = 375). Confirmatory factor analysis was performed both on the total sample and on the two subsamples through a multi-group approach; associations between cohesion and the duration of belonging to the team were also explored. Results confirmed the four-factor structure proposed by Carron's original model even though some items with low loadings were eliminated. No significant associations were found between team cohesion and the duration of belonging to the team.


#6 Cardiovascular health profile of elite female football players compared to untrained controls before and after short-term football training
Authors: Randers MB, Andersen LJ, Orntoft C, Bendiksen M, Johansen L, Horton J, Hansen PR, Krustrup P.
Reference: J Sports Sci. 2013 Jul 8. [Epub ahead of print]
Summary:  This study examined the intermittent exercise performance and cardiovascular health profile in elite female football players in comparison to untrained young women, as well as a subgroup subjected to football training 2x1 h · week-1 for 16 weeks. Twenty-seven Danish national team players (elite trained, ET) and 28 untrained women (UT) underwent dual-energy X-ray absorptiometry-scanning (DXA), comprehensive transthoracic echocardiography, treadmill and Yo-Yo Intermittent Endurance level 2 (IE2) testing. Eight women in UT were also tested after the football training period. Maximal oxygen uptake rate (VO2max), peak ventilation and peak lactate were 40, 18 and 51% higher (P< 0.01) in ET than UT, respectively. Cardiac dimensions and function were greater in ET than UT, with left ventricular diastolic diameter, right ventricular diastolic diameter, tricuspid annular plane systolic excursion (TAPSE) and peak transmitral flow in early diastole divided by peak transmitral flow velocity in late diastole during atrial contraction (E/A-ratio) being 13, 19, 27 and 41%, respectively, greater in ET than UT (P< 0.001 to< 0.05). Yo-Yo IE2 performance was 7-fold higher in ET than UT (1772 ± 508 vs. 234 ± 66 m, P< 0.001), fat mass was 51% lower (P< 0.001) and high density lipoprotein (HDL) cholesterol levels were 20% higher (P< 0.01). Sixteen weeks of football elevated VO2max and Yo-Yo IE2 performance by 16 and 40%, respectively, and lowered fat mass by 6%. Cardiac function was markedly improved by 16 weeks of football training with 26 and 46% increases in TAPSE and E/A ratio, respectively, reaching levels comparable to ET. In summary, elite female football players have a superior cardiovascular health profile and intermittent exercise performance compared to untrained controls, but short-term football training can markedly improve the cardiovascular health status.


#7 Musculoskeletal health profile for elite female footballers versus untrained young women before and after 16 weeks of football training
Authors: Jackman SR, Scott S, Randers MB, Orntoft C, Blackwell J, Zar A, Helge EW, Mohr M, Krustrup P.
Reference: J Sports Sci. 2013 Jul 8. [Epub ahead of print]
Summary: We investigated the musculoskeletal health profile of elite female football players (ET) in comparison to untrained (UT) young women subjected to 16 weeks of football training (2 × 1 h per week). DXA scans, blood sampling, sprint testing and Flamingo postural balance testing were carried out for 27 Danish national team players and 28 untrained women, with eight women being tested after training. At baseline total BMD and BMC were 13% (1.305 ± 0.050 versus 1.159 ± 0.056 g · cm-2) and 23% (3047 ± 235 versus 2477 ± 526 g) higher (P <0.001) and leg BMD and BMC were 24 and 28% higher (P <0.01) in ET than in UT. Resting plasma osteocalcin was 45% higher in ET than in UT (28.8 ± 10.9 versus 19.9 ± 9.9 µg · L-1, P <0.05). Total lean body mass was 14% higher (50.4 ± 3.3 versus 44.3 ± 4.0 kg) in ET compared with UT, with no difference in total body mass. The number of Flamingo test falls was 56-63% less (P <0.01) and 30 m sprinting speed was 31% faster (P <0.001) in ET than UT. After 16 weeks of football training for UT, lean body mass increased by 1.4 ± 0.5 kg and the number of left leg falls decreased by 29% (P <0.05). No significant changes occurred in BMD or BMC, but plasma osteocalcin increased (P <0.05) by 37%. In summary, elite women footballers have an impressive musculoskeletal health profile compared with untrained controls, but short-term football training seems to reduce the risk of falls and increase bone formation.


#8 Cardiovascular effects of 3 months of football training in overweight children examined by comprehensive echocardiography: a pilot study
Authors: Hansen PR, Andersen LJ, Rebelo AN, Brito J, Hornstrup T, Schmidt JF, Jackman SR, Mota J, Rêgo C, Oliveira J, Seabra A, Krustrup P.
Reference: J Sports Sci. 2013 Jul 8. [Epub ahead of print]
Summary:  We examined effects of a 3-month football training programme in overweight children using comprehensive echocardiography and peripheral arterial tonometry. Twenty preadolescent overweight children (17 boys, 3 girls aged 8-12 yrs; body mass index [BMI] ≥ 85th percentile) participated in a structured 3-month football training programme, consisting of 4 weekly 60-90 min sessions with mean heart rate (HR) > 80% of HRmax (football group, FG). A parallel control group (CG) included 11 children (7 boys, 4 girls) of equivalent age from an obesity clinic. After 3 months, systolic blood pressure was unchanged in FG, but had increased in CG (112 [s 6] vs. 122 [10] mmHg, P = 0.02). FG demonstrated increased left ventricular (LV) posterior wall diameter (0.60 [0.07] vs. 0.68 [0.10] cm, P < 0.001) and an improved right ventricular systolic function determined by tricuspid annular plane systolic excursion (TAPSE, 2.01 [0.29] vs. 2.27 [0.28] cm, P = 0.003). Measures of LV systolic function showed only discrete alterations and two-dimensional (2D) global strain was not changed. After 3 months, global isovolumetric relaxation time (IVRTglobal) had increased in FG (64.0 [7.5] vs. 73.9 [9.4] ms, P < 0.001) while other examined LV diastolic function variables were not altered. No echocardiographic changes were observed in CG. Between-group differences in pre-post delta values were observed for systolic blood pressure, TAPSE, and IVRTglobal (P = 0.02-0.03). We conclude that short-term football training may have positive structural and functional effects on the cardiovascular system in overweight preadolescent children.