Latest research in football - week 22 - 2013

Latest research in footall

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 Aerodynamic drag of modern soccer balls
Authors: Asai T, Seo K.
Reference: Springerplus. 2013 Apr 19;2(1):171. Print 2013 Dec.
Summary: Soccer balls such as the Adidas Roteiro that have been used in soccer tournaments thus far had 32 pentagonal and hexagonal panels. Recently, the Adidas Teamgeist II and Adidas Jabulani, respectively having 14 and 8 panels, have been used at tournaments; the aerodynamic characteristics of these balls have not yet been verified. Now, the Adidas Tango 12, having 32 panels, has been developed for use at tournaments; therefore, it is necessary to understand its aerodynamic characteristics. Through a wind tunnel test and ball trajectory simulations, this study shows that the aerodynamic resistance of the new 32-panel soccer ball is larger in the high-speed region and lower in the middle-speed region than that of the previous 14- and 8-panel balls. The critical Reynolds number of the Roteiro, Teamgeist II, Jabulani, and Tango 12 was ~2.2 × 105 (drag coefficient, C d  ≈ 0.12), ~2.8 × 105 (C d  ≈ 0.13), ~3.3 × 105 (C d  ≈ 0.13), and ~2.4 × 105 (C d  ≈ 0.15), respectively. The flight trajectory simulation suggested that the Tango 12, one of the newest soccer balls, has less air resistance in the medium-speed region than the Jabulani and can thus easily acquire large initial velocity in this region. It is considered that the critical Reynolds number of a soccer ball, as considered within the scope of this experiment, depends on the extended total distance of the panel bonds rather than the small designs on the panel surfaces

#2 Effects of carbohydrate-hydration strategies on glucose metabolism, sprint performance and hydration during a soccer match simulation in recreational players
Authors: Kingsley M, Penas-Ruiz C, Terry C, Russell M.
Reference: J Sci Med Sport. 2013 May 20. pii: S1440-2440(13)00097-2. doi: 10.1016/j.jsams.2013.04.010. [Epub ahead of print]
Summary: This study compared the effects of three carbohydrate-hydration strategies on blood glucose concentration, exercise performance and hydration status throughout simulated soccer match-play. After familiarization, 14 recreational soccer players completed the soccer match simulation on three separate occasions. Participants consumed equal volumes of 9.6% carbohydrate-caffeine-electrolyte (~6mg/kg BW caffeine) solution with carbohydrate-electrolyte gels (H-CHO), 5.6% carbohydrate-electrolyte solution with electrolyte gels (CHO) or electrolyte solution and electrolyte gels (PL). Blood samples were taken at rest, immediately before exercise and every 15min during exercise (first half: 15, 30, 45min; second half: 60, 75, 90min). Supplementation influenced blood glucose concentration (time×treatment interaction: p<0.001); however, none of the supplementation regimes were effective in preventing a drop in blood glucose at 60min. Mean sprint speed was 3±1% faster in H-CHO when compared with PL (treatment: p=0.047). Supplementation caused a 2.3±0.5% increase in plasma osmolality in H-CHO (p<0.001) without change in CHO or PL. Similarly, mean sodium concentrations were 2.1±0.4% higher in H-CHO when compared with PL (p=0.006). Combining high carbohydrate availability with caffeine resulted in improved sprint performance and elevated blood glucose concentrations throughout the first half and at 90min of exercise; however, this supplementation strategy negatively influenced hydration status when compared with 5.6% carbohydrate-electrolyte and electrolyte solutions

#3 Acute effects of proprioceptive neuromuscular facilitation and static stretching on maximal voluntary contraction and muscle electromyographical activity in indoor soccer players
Authors: Reis ED, Pereira GB, de Sousa NM, Tibana RA, Silva MF, Araujo M, Gomes I, Prestes J.
Reference: Clin Physiol Funct Imaging. 2013 May 6. doi: 10.1111/cpf.12047. [Epub ahead of print]
Summary: The aim was to investigate and compare the effects of proprioceptive neuromuscular facilitation (PNF) and static stretching (SS) on maximal voluntary contraction (MVC) and muscle activation in indoor soccer players. Thirty-three young adult men were divided into two groups: (i) sedentary and (ii) trained. Each group completed three different experimental trials: SS, PNF and no stretching (NS). The MVC of knee extension was evaluated before and immediately after each condition along with electromyography from the vastus lateralis (VL) and rectus femoris (RF) muscles of the dominant leg. PNF or SS techniques induced no decrease on MVC and muscle electromyographical activity in indoor soccer players (P>0·05). The electromyography of the RF and VL was lower after SS only in the sedentary group (P≤0·05). Short-duration PNF or SS has no effect on isometric MVC and muscle activity in indoor soccer players

#4 The Order of Concurrent Training Does not Affect Soccer-Related Performance Adaptations
Authors: McGawley K, Andersson PI.
Reference: Int J Sports Med. 2013 May 22. [Epub ahead of print]
Summary: Despite the wealth of evidence regarding physical training strategies in soccer, there is little information regarding soccer-specific concurrent training and the effects of training order. The current study aimed to: i) quantify the effects of concurrent high-intensity run-based training (HIT) and strength- and power-based training (STR) on soccer-specific performance, and ii) investigate the order effect of completing HIT and STR either first or second within training sessions. Eighteen semi- and fully-professional players completed a battery of field- and gym-based tests before and after a 5-week pre-season training intervention. Players were pair-matched and completed 3 sessions per week of HIT followed by STR (n=9) or STR followed by HIT (n=9). ANCOVA tests revealed no differences between groups for changes in any of the measures (p>0.05). However, a training effect was observed for all measures (p<0.05), with 10-m sprint, 6×30-m repeated sprint, 40-m agility and Yo-Yo test performances improving by 1.8±2.6%, 1.3±1.8%, 1.0±1.5% and 19.4±23.4%, respectively (n=18). In conclusion, there was a positive effect of the concurrent training approach on key measures of soccer performance, but the order of completing HIT and STR appears inconsequential to performance adaptations.

#5 Relative Age, Biological Maturation and Anaerobic Characteristics in Elite Youth Soccer Players
Authors: Deprez D, Coutts AJ, Fransen J, Deconinck F, Lenoir M, Vaeyens R, Philippaerts R.
Reference: Int J Sports Med. 2013 May 22. [Epub ahead of print]
Summary: The aims of the study were to investigate the presence of a relative age effect (RAE) and the influence of birth quarter on anthropometry, biological maturity and anaerobic parameters in 374 elite Belgian youth soccer players. The sample was divided into 3 age groups, each subdivided into 4 birth quarters (BQ). Players had their APHV estimated and height, weight, SBJ, CMJ, sprint 5 and 30 m were assessed. Overall, more players were born in BQ1 (42.3%) compared with players born in BQ4 (13.7%). Further, MANCOVA revealed no differences in all parameters between the 4 BQ's, controlled for age and APHV. These results suggest that relatively youngest players can offset the RAE if they enter puberty earlier. Furthermore, the results demonstrated possible differences between BQ1 and BQ4, suggesting that caution is necessary when estimating differences between players because of large discrepancies between statistical and practical significance. These findings also show that coaches should develop realistic expectations of the physical abilities of younger players and these expectations should be made in the context of biological characteristics rather than chronological age-based standards.

#6 Effect of strength and high-intensity training on jumping, sprinting and intermittent endurance performance in prepubertal soccer players
Authors: Ferrete C, Requena B, Suarez-Arrones L, Sáez de Villarreal E.
Reference: J Strength Cond Res. 2013 May 21. [Epub ahead of print]
Summary: The purpose of this study was to examine the effects of a 26-week on-field combined strength and high-intensity training on physical performance capacity among prepubertal soccer players who were undetraking a competitive phase of training. Twenty-four prepubertal soccer players between the age of 8-9 years were randomly assigned to 2 groups: a control (C) (n=13) and an experimental group (S) (n=11). Both groups performed an identical soccer training program, while the S group also performed combined strength and high-intensity training before the soccer specific training. The 15-m sprint time (sec), countermovement vertical jump (CMJ) displacement, Yo-Yo intermittent endurance test (Yo-YoIE), and Sit & Reach flexibility were each measured before (baseline) and after 9 (T2), 18 (T3) and 26 weeks (post-test) of training. There were no significant differences between the groups in any of the variables tested at baseline. After 26 weeks significant improvements were found in CMJ (6.72%; ES = 0.37), Yo-YoIE (49.57%, ES = 1.39), and Flexibility (7.26%; ES = 0.37) variables for the S group. Conversely, significant decreases were noted for the CMJ (-10.82%; ES = 0.61) and flexibility (-13.09%; ES = 0.94) variables in C group. A significant negative correlation was found between 15m sprint time and CMJ (r=-0.77) and Yo-YoIE (r=-0.77) in S group. Specific combined strength and high-intensity training in prepubertal soccer players for 26 weeks produced a positive effect on performance qualities highly specific to soccer. Therefore, we propose modifications to current training methodology for prepubertal soccer players to include strength and high-intensity training for athlete preparation in this sport

#7 The presence of bilateral imbalance of the lower limbs in elite youth soccer players of different ages

Authors: Atkins S, Hesketh C, Sinclair J.
Reference: J Strength Cond Res. 2013 May 21. [Epub ahead of print]
Summary: The aim of this study was to examine bilateral differences in ground reaction forces, measured during a deep squat exercise, in a population of elite youth soccer players. Bilateral muscle balance is a key component in promoting musculoskeletal health of performers, yet there is a limited evidence base investigating such imbalances in youth. Seventy-four subjects were assigned to performance groups according to chronological age (Under 13, 14, 15, 16, 17 yr). Analysis of physical maturity status revealed that very few players were classified as 'early' or 'late' maturers. Players completed an overhead deep squat exercise, as part of pre-season functional movement screening. Peak ground reaction forces were assessed using a twin force plate system. Significant differences (p ≤ 0.05) were identified between right and left side PGRF for all groups except the youngest (U13) and oldest (U17). Non-dominant 'sides' showed the highest levels of PGRF across all groups. The magnitude of PGRF was not significantly different both within and between groups, except for the left side in the U13 to U15 groups (p = 0.04). Results from this study show that performance asymmetry is marked in adolescence. There appears a 'trigger point' during the early stage of adolescence, when bilateral imbalances become marked. These differences do seem to reduce during the later stages of adolescence. Correct attention to focussed training, designed to remediate any imbalance, is warranted in adolescent groups. This is important with respect of the key associations between bilateral asymmetry and risk of injury

#8 The effect of high and low percentage ball possession on physical and technical profiles in English FA Premier League soccer matches
Authors: Bradley PS, Lago-Peñas C, Rey E, Diaz AG.
Reference: J Sports Sci. 2013 May 22. [Epub ahead of print]
Summary: The aim of this study was to examine the effects of high (HPBPT) and low percentage ball possession teams (LPBPT) on physical and technical profiles in elite soccer matches. Match performance data were collected from players in the English FA Premier League (n = 810) using a multiple-camera computerised tracking system. Physical indicators such as the total (10690 ± 996 vs 10778 ± 979 m; effect size [ES] = 0.11) and high-intensity running distance covered in matches (931 ± 299 vs 938 ± 311 m; ES = 0.13) did not differ between HPBPT and LPBPT. However, high-intensity running with ball possession in HPBPT was 31% higher (P < 0.01) than LPBPT (449 ± 266 vs 343 ± 236 m; ES = 0.42) but 22% lower without ball possession (423 ± 153 vs 539 ± 177 m; ES = 0.73). Players in HPBPT performed 44% more (P < 0.01) passes than those in LPBPT (35.3 ± 14.2 vs 24.6 ± 11.2; ES = 0.83). This trend was also evident (P < 0.05) for successful passes, received passes, touches per possession, shots, dribbles and final-third entries (ES range of 0.20-0.94). Central defenders of LPBPT covered 33% less (P < 0.01) high-intensity running with ball possession than central defenders of HPBPT. While fullbacks, attackers, central and wide midfielders of LPBPT covered more (P < 0.01) high-intensity running without and less with ball possession than their HPBPT counterparts (ES range of 0.91-1.23). Technical indicators such as total passes and passes received were higher (P < 0.01) across all positions in HPBPT than LPBPT (ES range of 0.82-1.52). The data demonstrate that percentage ball possession does not influence the overall activity profile of a team but impacts on the composition of high-intensity running efforts (with and without ball) and some technical elements of performance. Position-specific changes in physical and technical profiles were evident for teams employing different ball possession percentages and this information could aid training preparation.

#9 The strange flight behaviour of slowly spinning soccer balls
Authors: Mizota T, Kurogi K, Ohya Y, Okajima A, Naruo T, Kawamura Y.
Reference: Sci Rep. 2013 May 22;3:1871. doi: 10.1038/srep01871.
Summary: The strange three-dimensional flight behaviour of slowly spinning soccer balls is one of the most interesting and unknown phenomenon associated with the trajectories of sports balls. Many spectators have experienced numerous exciting and emotional instances while observing the curious flight behaviour of these balls. We examine the aerodynamic mechanisms of erratic ball behaviours through real flight observations, unsteady force measurements and flow pattern visualisations. The strange behaviour is elucidated by the relationship between the unsteady forces on the ball and the wake flow. The irregular changes in position for twin longitudinal vortices have already been discovered in the supercritical Reynolds number region of a sphere with a smooth surface. This finding is applicable to the strange behaviour of the flight of soccer balls with this supercritical flow. The players, spectators, and television viewers will gain greater insight into the effects of soccer ball flights.

#10 Clinical recovery of two hip adductor longus ruptures: a case-report of a soccer player
Authors: Thorborg K, Petersen J, Nielsen MB, Hölmich P.
Reference: BMC Res Notes. 2013 May 22;6(1):205. [Epub ahead of print]
Summary: Non-operative treatment of acute hip adductor longus ruptures in athletes has been described in the literature. However, very limited information concerning the recovery of this type of injury exists. This case represented a unique possibility to study the recovery of two acute adductor longus ruptures, using novel, reliable and validated assessment methods. A 22-year old male soccer player (Caucasian) sustained two subsequent acute adductor longus ruptures, one in each leg. The injuries occurred 10 months apart, and were treated non-surgically in both situations. He was evaluated using hip-strength assessments, self-report and ultrasonography until complete muscle-strength recovery of the hip adductors had occurred. The player was able to participate in a full soccer training session without experiencing pain 15 weeks after the first rupture, and 12 weeks after the second rupture. Full hip adductor muscle-strength recovery was obtained 52 weeks after the first rupture and 10 weeks after the second rupture. The adductor longus injuries, as verified by initial ultrasonography (10 days post-injury), showed evidence of a complete tendon rupture in both cases, with an almost identical imaging appearance. It was only at 6 and 10 weeks ultrasonographic follow-up that the first rupture was found to include a larger anatomical area than the second rupture. From this case we can conclude that two apparently similar hip adductor longus ruptures, verified by initial ultrasonography (10 days post-injury), can have very different hip adductor strength recovery times. Assessment of adductor strength recovery may therefore in the future be a useful and important additional measure for determining when soccer players with hip adductor longus ruptures can return safely to play.

#11 Effects of pacing, status and unbalance in time motion variables, heart rate and tactical behaviour when playing 5-a-side football small-sided games
Authors: Sampaio JE, Lago C, Gonçalves B, Maçãs VM, Leite N.
Reference: J Sci Med Sport. 2013 May 14. pii: S1440-2440(13)00092-3. doi: 10.1016/j.jsams.2013.04.005. [Epub ahead of print]
Summary: The purpose of this study was to compare time-motion variables, heart rate and players' tactical behaviour according to game pace (slow, normal or fast), status (winning and losing) and team unbalance (superiority and inferiority) in football 5-a-side small-sided games. To identify the most discriminating variables in classifying performances according to these constraints. The data were gathered using global positioning systems (5Hz) in 5-a-side small-sided games (7×5min) played by twenty-four footballers. The tactical performance was measured using dynamical positioning variables, processed by non-linear signal processing techniques (approximate entropy). ANOVA models were used to compare between constraints and discriminant analyses to identify the variables that best discriminate between pacing and status×unbalance constraints. The fast paced games had the highest mean speed value, followed by normal and slow paced games (8.2±0.6kmh-1, 7.8±0.5kmh-1 and 6.2±0.4kmh-1, respectively). The stronger predictor variables of pacing were the randomness in distance to team centroid and the distances covered above 13kmh-1. The results also changed according to game status and team unbalance. The strongest predictor variables were the distance covered bellow 6.9kmh-1, distance and randomness to team centroid, with higher values when winning in superiority conditions. Practice task design manipulating game pace, status and team unbalance significantly influenced the emergent behavioural dynamics. Collective positioning variables were more accurate in discriminating these constraints and, therefore, need to be considered when planning and monitoring performance.

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