Latest research in football - week 19 Part II - 2014

Latest research in football

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 Effects and sustainability of a 13-day high-intensity shock microcycle in soccer
Reference: J Sports Sci Med. 2014 May 1;13(2):259-65. eCollection 2014.
Authors: Wahl P, Güldner M, Mester J.
Summary: The preseason in soccer is a short period of 6-8 weeks where conditional abilities, technical and tactical elements need to be trained. Therefore, time is lacking to perform long term preparation periods for different abilities, especially endurance training. There is evidence that the implementation of high-intensity shock microcycles in preseason training could be one way to improve physical performance in a short period of time. Therefore, the purpose of the present study was to examine the effects and the sustainability of a high-intensity shock microcycle on soccer specific performance. Over 2 weeks, 12 male soccer players (26.1 ± 4.5 years) performed 12 high-intensity training (HIT) sessions in addition to their usual training. Before (pre), 6 days (6d) and 25 days (25d) after training, subjects performed Counter Movement Jump (CMJ), Repeated-Sprint Ability (RSA) test and Yo-Yo Intermittent Recovery Test Level 2 (YYIR2). Mean sprint time (RSAMean) (cohen's d = -1.15), percentage decrement score (RSAIndex) (cohen's d = -1.99) and YYIR2 (cohen's d = +1.92) improved significantly from pre to 6d. 25d after, values showed a significant reduction for YYIR2 (cohen's d = -0.81) and small to moderate but not significant increase for RSAMean (cohen's d = +0.37) and RSAIndex (cohen's d = +0.7) compared to 6d values. Small but no significant increases were found for CMJ (cohen's d = +0.33) and no significant and substantial changes were found for RSABest (cohen's d = -0.07) from pre to 6d. For competitive soccer players, block periodization of HIT offers a promising way to largely improve RSA and YYIR2 in a short period of time. Despite moderate to large decreases in RSAIndex and YYIR2 performance in the 19 day period without HIT, values still remained significantly higher 25d after the last HIT session compared to pre-values. However, it might be necessary to include isolated high-intensity sessions after a HIT training block in order to maintain the higher level of YYIR2 and RSAIndex performance. Key pointsHIT shock microcycle increases performance in semi-professional soccer players in a short period of time.Despite moderate to large decreases in performance in the 19 day period without HIT, values still remained significantly higher 25d after the last HIT session compared to pre-values.This kind of training block increases YYIR2 performance and the ability to repeated sprints, based on the RSAIndex.

#2 Effect of Anticipation on Lower Extremity Biomechanics During Side- and Cross-Cutting Maneuvers in Young Soccer Players
Reference: Am J Sports Med. 2014 Apr 30. [Epub ahead of print]
Authors: Kim JH, Lee KK, Kong SJ, An KO, Jeong JH, Lee YS.
Summary: Less mature athletes exhibit biomechanical parameters during cutting maneuvers that may place these athletes at greater risk for injury than their more mature counterparts, especially if the maneuvers are unanticipated. However, most studies on risk factors for anterior cruciate ligament (ACL) injury have focused on neuromuscular and knee kinematic differences between the sexes, not on the biomechanical parameters between specific sporting maneuvers. Two hypothesis were given. 1) Anticipation will have a greater effect than the type of cutting maneuver (side- vs cross-cutting) in terms of the biomechanical risk factors for ACL injuries, and 2) the biomechanical risk factors will be different between the 2 types of maneuvers. Thirty-seven young, male middle school soccer players participated in this study. Three-dimensional motion analysis featuring ground-reaction force and electromyography of the right leg was used. Kinematics, kinetics, and electromyography data for each athlete were analyzed during anticipated and unanticipated side- and cross-cutting maneuvers. The differences between anticipated and unanticipated states as well as between side- and cross-cutting maneuvers were calculated and compared. After unanticipated side-cutting, the time to peak ground-reaction force was longer and peak values were smaller compared with anticipated side-cutting. Flexion, valgus, and internal rotations in the knee joint were larger, and greater flexion and valgus moments were observed. The vastus lateralis and vastus medialis showed lower activity, and the lateral gastrocnemius showed higher activity after unanticipated side-cutting maneuvers. With unanticipated cross-cutting, the time to peak ground-reaction force was longer and peak values were smaller compared with anticipated cross-cutting, and the lateral gastrocnemius showed higher activity. Differences in the peak values of the mediolateral and vertical forces were smaller in the cross-cutting maneuver than in side-cutting. Changes in flexion and adduction of the hip joint, flexion of the knee joint, and inversion of the ankle joint were larger during side-cutting. Although there were some interactions between direction and anticipation, anticipating a cutting maneuver generally had a greater effect than the type of maneuver when there was no significant interaction. Increases in the valgus angle and moment of the knee joint and higher lateral gastrocnemius activity during the late period showed an association with ACL injury risk factors during side-cutting, and higher lateral gastrocnemius activity during the early period showed an association with injury risk factors during cross-cutting.

#3 Effects of age, maturity and body dimensions on match running performance in highly trained under-15 soccer players
Reference: J Sports Sci. 2014 May 1:1-8. [Epub ahead of print]
Authors: Buchheit M, Mendez-Villanueva A.
Summary: The aim of the present study was to compare, in 36 highly trained under-15 soccer players, the respective effects of age, maturity and body dimensions on match running performance. Maximal sprinting (MSS) and aerobic speeds were estimated. Match running performance was analysed with GPS (GPSport, 1 Hz) during 19 international friendly games (n = 115 player-files). Total distance and distance covered >16 km h-1 (D > 16 km h-1) were collected. Players advanced in age and/or maturation, or having larger body dimensions presented greater locomotor (Cohen's d for MSS: 0.5-1.0, likely to almost certain) and match running performances (D > 16 km h-1: 0.2-0.5, possibly to likely) than their younger, less mature and/or smaller teammates. These age-, maturation- and body size-related differences were of larger magnitude for field test measures versus match running performance. Compared with age and body size (unclear to likely), maturation (likely to almost certainly for all match variables) had the greatest impact on match running performance. The magnitude of the relationships between age, maturation and body dimensions and match running performance were position-dependent. Within a single age-group in the present player sample, maturation had a substantial impact on match running performance, especially in attacking players. Coaches may need to consider players' maturity status when assessing their on-field playing performance.

#4 Movement profiles of elite women soccer players during international matches and the effect of opposition's team ranking
Reference: J Sports Sci. 2014 May 1:1-7. [Epub ahead of print]
Authors: Hewitt A, Norton K, Lyons K.
Summary: Movement patterns in elite men's soccer have been reported in depth, but less research exists for women's soccer. Aims of the study were to identify the movement profiles of elite women soccer players in international competition and examine the effect the level of opposition, based on Federation Internationale de Football Association (FIFA) rankings, had on the physical demands of the game. MinimaxX athlete tracking devices were used by 15 players during 13 international matches against opponent teams of varying ability. Total distance covered averaged 9292 ± 175 m. There was a decrease in high-intensity running (HIR) in the 60- to 75-min and 75- to 90-min periods compared to the 0- to 15-min period of 22.4% and 26.1%, respectively (P = 0.022, P = 0.004) although sprint distances remained unchanged across game periods. HIR distances covered were significantly greater for midfielders versus defenders, while defenders had lower sprinting compared to both midfielders and attackers. Stronger opponents elicited less HIR and greater low-speed activity (LSA) compared to playing teams of similar or lower ranking. These results are important to coaches to prepare players for international competition and show the differing demands required depending on the ability of the opponents.

#5 Exercise performance and cardiovascular health variables in 70-year-old male soccer players compared to endurance-trained, strength-trained and untrained age-matched men
Reference: J Sports Sci. 2014 May 1:1-9. [Epub ahead of print]
Authors: Randers MB, Andersen JL, Petersen J, Sundstrup E, Jakobsen MD, Bangsbo J, Saltin B, Krustrup P.
Summary: The aim was to investigate performance variables and indicators of cardiovascular health profile in elderly soccer players (SP, n = 11) compared to endurance-trained (ET, n = 8), strength-trained (ST, n = 7) and untrained (UT, n = 7) age-matched men. The 33 men aged 65-85 years underwent a testing protocol including measurements of cycle performance, maximal oxygen uptake (VO2max) and body composition, and muscle fibre types and capillarisation were determined from m. vastus lateralis biopsy. In SP, time to exhaustion was longer (16.3 ± 2.0 min; P < 0.01) than in UT (+48%) and ST (+41%), but similar to ET (+1%). Fat percentage was lower (P < 0.05) in SP (-6.5% points) than UT but not ET and ST. Heart rate reserve was higher (P < 0.05) in SP (104 ± 16 bpm) than UT (+21 bpm) and ST (+24 bpm), but similar to ET (+2 bpm), whereas VO2max was not significantly different in SP (30.2 ± 4.9 ml O2 · min-1 · kg-1) compared to UT (+14%) and ST (+9%), but lower (P < 0.05) than ET (-22%). The number of capillaries per fibre was higher (P < 0.05) in SP than UT (53%) and ST (42%) but similar to ET. SP had less type IIx fibres than UT (-12% points). In conclusion, the exercise performance and cardiovascular health profile are markedly better for lifelong trained SP than for age-matched UT controls. Incremental exercise capacity and muscle aerobic capacity of SP are also superior to lifelong ST athletes and comparable to endurance athletes.

#6 Nutritional practices associated with low energy availability in Division I female soccer players
Reference: J Sports Sci. 2014 May 1:1-11. [Epub ahead of print]
Authors: Reed JL, De Souza MJ, Kindler JM, Williams NI.
Summary: The purpose of this study was to examine macronutrient intake, energy density and energy intake distribution that may be associated with low energy availability (EA) in Division I female soccer players. The energy intake, exercise energy expenditure and EA of 19 participants (18-21 years) was assessed during the pre-, mid- and postseasons. Repeated measures analysis of variance was performed to examine the changes across the season. Chi-square analysis was performed to examine the distribution of participants meeting the American College of Sports Medicine recommendations for carbohydrate and protein consumption. Independent t-tests were used to compare differences between groups. The proportion of athletes who did not meet the American College of Sports Medicine recommendations for carbohydrate intake (6-10 g . kg-1 BW) was significantly greater in the low (<30 kcal . kg-1 LBM) than higher (≥30 kcal . kg-1 LBM) EA group (χ2 (1) = 7.5; P = 0.006). Participants with low compared to higher EA consumed a lower energy dense dinner (0.8 ± 0.1 vs. 1.4 ± 0.1 kcal . g-1; P = 0.004) after a soccer match during midseason. No differences in the percentage (%) of kilocalories from food (84.5 ± 2.0% vs. 84.7 ± 2.6%), sports drinks (7.3 ± 1.4% vs. 6.0 ± 3.2%), other drinks (7.6 ± 1.5 % vs. 6.0 ± 1.5%) or bars/gels/beans (1.7 ± 0.6 vs. 3.0 ± 1.5) were observed in participants with low compared to higher EA (P > 0.05) during the pre- and midseasons. Identifying inadequate carbohydrate intake and the practice of consuming lower energy dense meals may be important in preventing low EA conditions and consequently the Female Athlete Triad.

#7 Influence of Instruction on Velocity and Accuracy in Soccer Kicking of Experienced Soccer Players
Reference: J Mot Behav. 2014 Apr 28:287-291. [Epub ahead of print]
Authors: van den Tillaar R1, Ulvik A.
Summary: The authors' aim was to investigate the speed-accuracy tradeoff in soccer kicking with the dominant and nondominant foot by using different types of instructions prioritizing speed or accuracy in experienced soccer players. Ten male soccer players were randomly given 1 of the 4 instructions that differed in aspects of the kick they should emphasize and what the secondary aim would be (speed or accuracy). It was found that ball velocity was affected by instruction in the expected way: emphasis on accuracy and ball velocity reduced for both kicking feet. In addition kicking accuracy increased when emphasizing this, but only with the dominant foot indicating that Fitts' law only was found in kicks with the dominant foot.

#8 Neural underpinnings of superior action prediction abilities in soccer players
Reference: Soc Cogn Affect Neurosci. 2014 Apr 24. [Epub ahead of print]
Authors: Makris S, Urgesi C.
Summary: The ability to form anticipatory representations of ongoing actions is crucial for effective interactions in dynamic environments. In sports, elite athletes exhibit greater ability than novices in predicting other players' actions, mainly based on reading their body kinematics. This superior perceptual ability has been associated with a modulation of visual and motor areas by visual and motor expertise. Here, we investigated the causative role of visual and motor action representations in experts' ability to predict the outcome of soccer actions. We asked expert soccer players (outfield players and goalkeepers) and novices to predict the direction of the ball after perceiving the initial phases of penalty kicks that contained or not incongruent body kinematics. During the task we applied repetitive transcranial magnetic stimulation (rTMS) over the superior temporal sulcus (STS) and the dorsal premotor cortex (PMd). Results showed that STS-rTMS disrupted performance in both experts and novices, especially in those with greater visual expertise (i.e., goalkeepers). Conversely, PMd-rTMS impaired performance only in expert players (i.e., outfield players and goalkeepers), who exhibit strong motor expertise into facing domain-specific actions in soccer games. These results provide causative evidence of the complimentary functional role of visual and motor action representations in experts' action prediction.

#9 Mortality on match days of the German national soccer team: a time series analysis from 1995 to 2009
Reference: J Epidemiol Community Health. 2014 May 8. doi: 10.1136/jech-2013-202844. [Epub ahead of print]
Authors: Medenwald D, Kuss O.
Summary: There is inconsistent evidence on population mortality, especially cardiovascular disease mortality, on match days of national soccer teams during particular international tournaments. This study examines the number of deaths in Germany on match days of the national soccer team during a long-term period including several tournaments. We analysed all registered daily deaths in Germany from 1995 to 2009 (11 225 966 cases) using time series analysis methods. Following the Box/Jenkins approach, we applied a seasonal autoregressive integrated moving average model. To assess the effect of match days, we performed an intervention analysis by including a transfer function model representing match days of the national team in the statistical analyses. We conducted separate analyses for all matches and for matches during international tournaments (European and World Championships) only. Time series and results were stratified in terms of sex, age (<50 years, 50-70 years, >70 years) and cause of death (cardiovascular deaths, injuries, others). We performed a further independent analysis focusing only on the effect of match results (victory, loss, draw) and kind of tournament (international championships, qualifications, friendly matches). Most of the results did not indicate a distinct effect of matches of the national team on general mortality. Moreover, all null value deviations were small when compared with the average number of daily deaths (n=2270). There is no relevant increase or decrease in mortality on match days of the German national soccer team.

#10 Genomics DNA Profiling in Elite Professional Soccer Players: A Pilot Study
Reference: Transl Med UniSa. 2014 Apr 24;9:18-22. eCollection 2014.
Authors: Kambouris M, Del Buono A, Maffulli N
Summary: Functional variants in exonic regions have been associated with development of cardiovascular disease, diabetes and cancer. Athletic performance can be considered a multi-factorial complex phenotype. Genomic DNA was extracted from buccal swabs of seven soccer players from the Fulham football team. Single nucleotide polymorphism (SNPs) genotyping was undertaken. To achieve optimal athletic performance, predictive genomics DNA profiling for sports performance can be used to aid in sport selection and elaboration of personalized training and nutrition programs. Predictive DNA profiling may be able to detect athletes with potential or frank injuries, or screening and selection of future athletes, and can help them to maximize utilization of their potential and improve performance in sports. The aim of this study is to provide a wide scenario of specific genomic variants that an athlete carries, to implement which measures should be taken to maximize the athlete's potential.

#11 Assessment of neuromuscular risk factors for anterior cruciate ligament injury through tensiomyography in male soccer players
Reference: Knee Surg Sports Traumatol Arthrosc. 2014 May 8. [Epub ahead of print]
Authors: Alentorn-Geli E, Alvarez-Diaz P, Ramon S, Marin M, Steinbacher G, Boffa JJ, Cuscó X, Ballester J, Cugat R.
Summary: To investigate the role of mechanical and contractile properties of skeletal muscles of the thigh, assessed through tensiomyography (TMG), as risk factors for anterior cruciate ligament (ACL) injury in male soccer players. Male soccer players with confirmed ACL tear included in this study underwent resting TMG assessment of thigh muscles of the uninjured side. The same values were obtained from a sex-, sports level-matched control group in both sides. The maximal displacement (Dm), delay time (Td), contraction time (Tc), sustained time (Ts), and half-relaxation time (Tr) were obtained for the following muscles in all subjects: vastus medialis (VM), vastus laterals (VL), rectus femoris (RF), semitendinosus (ST), and biceps femoris (BF). TMG values of the uninjured side in ACL-injured group were compared to mean values between both sides in the control subjects. There were 40 ACL-injured and 38 control individuals. The vast majority of TMG parameters were higher in the uninjured side of ACL-injured individuals compared to the control group. The VL-Tr, RF-Tc, RF-Ts, RF-Tr, and BF-Dm values were significantly higher in the uninjured side compared to the control group. Quadriceps muscles demonstrated more significant between-group differences than hamstring muscles. Specifically, RF was the muscle where most significant between-group differences were found. Resistance to fatigue and muscle stiffness in the hamstring muscles may be risk factors for ACL injury in male soccer players. In addition, a predominant impairment in TMG characteristics of the quadriceps over hamstrings may indicate an altered muscular co-contraction (imbalance) between both muscle groups, which might be another risk factor for ACL injury in this population. These findings should be taken into account when screening athletes at high risk of ACL injury and also to design adequate prevention programs for ACL injury in male soccer players.

#12 Applied Physiology of Female Soccer: An Update
Reference: Sports Med. 2014 May 7. [Epub ahead of print]
Authors: Datson N, Hulton A, Andersson H, Lewis T, Weston M, Drust B, Gregson W.
Summary: The popularity and professionalism of female soccer has increased markedly in recent years, with elite players now employed on either a professional or semi-professional basis. The previous review of the physiological demands of female soccer was undertaken two decades ago when the sport was in its relative infancy. Increased research coupled with greater training and competition demands warrants an updated review to consider the effect on physical performance and injury patterns. The physical demands of match-play along with the influence of factors such as the standard of competition, playing position and fatigue have been explored. Total distance covered for elite female players is approximately 10 km, with 1.7 km completed at high-speed (>18 km·h-1). Elite players complete 28 % more high-speed running and 24 % more sprinting than moderate-level players. Decrements in high-speed running distance have been reported between and within halves, which may indicate an inability to maintain high-intensity activity. Although the physical capacity of female players is the most thoroughly researched area, comparisons are difficult due to differing protocols. Elite players exhibit maximal oxygen uptake (VO2max) values of 49.4-57.6 mL·kg-1·min-1, Yo Yo Intermittent Endurance test level 2 (YYIE2) scores of 1,774 ± 532 m [mean ± standard deviation (SD)] and 20 m sprint times of 3.17 ± 0.03 s (mean ± SD). Reasons for the increased prevalence of anterior cruciate ligament injuries in females (2-6 times greater than males) are discussed, with anatomical, biomechanical loading and neuromuscular activation differences being cited in the literature. This review presents an in-depth contemporary examination of the applied physiology of the female soccer player.

#13 Changes in Functional Movement Screen Scores Over a Season in Collegiate Soccer and Volleyball Athletes
Reference: J Strength Cond Res. 2014 May 2. [Epub ahead of print]
Authors: Sprague PA, Mokha M, Gatens DR.
Summary: Changes in many aspects of physical capacity and athletic performance have been documented through the course of a competitive season in collegiate athletes. Movement pattern quality as measured by the Functional Movement ScreenTM (FMS) has recently been linked to performance and injury risk. The purpose of this study was to document the changes in functional movement patterns over a competitive season. Fifty-seven NCAA Division II athletes were screened using the FMS as part of the pre and post participation examination for their competitive seasons in 2012. Composite and individual FMS test scores for the pre and post season were compared to identify significant changes. The scores were also analyzed for changes in the number of asymmetries present and the frequency of a score of one in any of the tests. There were no significant interactions in the main effects for time or sport in the composite FMS scores. However, four individual tests did show significant change. The deep squat (Z=-3.260, p=.001) and inline lunge scores (Z=-3.498, p<.001) improved across all athletes, and the active straight leg raise (Z=-2.496, p=.013) and rotary stability scores (Z=-2.530, p=.011) worsened across all athletes. A reduction in the number of asymmetries (X2=4.258, p=.039) and scores of 1 (X2=26.148, p<.001) were also found. Changes in individual fundamental movement patterns occur through the course of a competitive season.

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