Latest research in football - week 52 - 2014

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 How perceiving additional targets modifies teams' tactical behavior during football small-sided games
Reference: Hum Mov Sci. 2014 Dec;38:241-50. doi: 10.1016/j.humov.2014.10.005. Epub 2014 Nov 15.
Authors: Travassos B, Gonçalves B, Marcelino R, Monteiro R, Sampaio J
Summary: This study aimed to measure how the change on targets information modifies teams' tactical behavior during football small-sided games. 20 male senior professional players divided in 4 teams of 5 players participated in the study. Each team played two small-sided games, one with 2 official targets with goalkeeper and one with 6 small targets. Positional data of each player were recorded using a 15Hz portable GPS. The distance between the centers of gravity (CG) of both team, the stretch index and the relative stretch index were measured and differences accessed via standardized differences, coefficient intervals and meta-analysis procedures. A moderate increase on the distance between the CG of each team and a small decrease on the stretch index and on the relative stretch index from 2 targets to the 6 targets games was observed. It was also identified that pitch location affected the interaction between teams. When the game was played in lateral corridors or defensive sectors, the differences between game conditions increased. Emphasizing the information for attacking team to shoot at goal, by manipulating the number of targets constrained tactical behavior of teams. The amplification of specific information on small-sided games can help coaches to promote players and teams' emergent adapted behaviors.

#2 Frequency and trends in foot and ankle injuries within an English Premier League Football Club using a new impact factor of injury to identify a focus for injury prevention
Reference: Foot Ankle Surg. 2014 Dec;20(4):237-40. doi: 10.1016/j.fas.2014.05.004. Epub 2014 May 24.
Authors: Jain N, Murray D, Kemp S, Calder J
Summary: Foot and ankle injuries are common in football. Prevention strategies exist in order to decrease the incidence of such injuries and minimize the number of days that a player is unavailable for selection. Injuries were recorded over a 4-season period while the team was playing in the English Premier League (EPL). We present the epidemiology of foot and ankle injuries within a professional football club and offer a calculation that may be of use in the future to identify areas of injury prevention. Anterior Talo-Fibular Ligament (ATFL) injuries and fifth metatarsal fractures were of high impact as they were both common and resulted in significant time periods where the player was unavailable. This is the first time an EPL club has been prepared to publish data regarding injury. Our findings may be used by others to focus their prevention strategies on the injuries with the highest impact.

#3 Effects of Eccentric Overload Bout on Change of Direction and Performance in Soccer Players
Reference: Int J Sports Med. 2014 Dec 19. [Epub ahead of print]
Authors: de Hoyo M, de la Torre A, Pradas F, Sañudo B, Carrasco L, Mateo-Cortes J, Domínguez-Cobo S, Fernandes O, Gonzalo-Skok O
Summary: The aims of this study were to analyse the effects of eccentric overload training (EOT) on kinetic parameters during change of direction (COD) and performance related to sprinting and jumping abilities. 20 male soccer players performed 2 different protocols: 1) 5-min cycling warm-up and 2) 5-min cycling warm-up+YoYo half-squat exercise. The outcome measured included vertical ground reaction force (vGRF) and propulsive force (PvGRF), time to vGRF (T_vGRF) and propulsive force (T_PvGRF), contact time (CT), eccentric (ECC_IMP), concentric (CONC_IMP) and total (TOT_IMP) impulses and moments (Mx, My and Mz) during 2 COD tasks. Additionally, subjects performed a counter-movement jump (CMJ) and 20 m sprint tests. Results showed a substantial better improvement (likely to almost certainly) in vGRF (ES: 0.84), vAGRF (ES: 0.72), CT (ES: 0.48), My (ES: 0.35), Mz (ES: 0.44) and ECC_IMP (ES: 0.45) during crossover cutting maneuver, whereas during side-step cutting maneuver Time_ECC (ES: 0.68), CT (ES: 0.64), vGRF (ES: 0.48) and My (ES: 0.47) were substantially enhanced (likely). Furthermore, substantial better performance was found in CMJ (ES: 0.47; very likely) and 20 m (ES: 0.20; possibly). In conclusion, EOT produced a better muscle activation during 2 different COD tasks and greater sprinting and jumping performance.

#4 PPARα gene variants as predicted performance-enhancing polymorphisms in professional Italian soccer players
Reference: Open Access J Sports Med. 2014 Dec 8;5:273-8. doi: 10.2147/OAJSM.S68333. eCollection 2014.
Authors: Proia P, Bianco A, Schiera G, Saladino P, Contrò V, Caramazza G, Traina M, Grimaldi KA, Palma A, Paoli A
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Summary: The PPARα gene encodes the peroxisome proliferator-activator receptor alpha, a central regulator of expression of other genes involved in fatty acid metabolism. The purpose of this study was to determine the prevalence of G allele of the PPARα intron 7 G/C polymorphism (rs4253778) in professional Italian soccer players. Sixty professional soccer players and 30 sedentary volunteers were enrolled in the study. Samples of venous blood were obtained at rest, in the morning, by conventional clinical procedures; blood serum was collected and total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides were measured. An aliquot of anticoagulant-treated blood was used to prepare genomic DNA from whole blood. The G/C polymorphic site in PPARα intron 7 was scanned by using the PCR-RFLP (polymerase chain reaction restriction fragment length polymorphism) protocol with TaqI enzyme. We found variations in genotype distribution of PPARα polymorphism between professional soccer players and sedentary volunteers. Particularly, G alleles and the GG genotype were significantly more frequent in soccer players compared with healthy controls (64% versus 48%). No significant correlations were found between lipid profile and genotype background. Previous results demonstrated an association of intron 7 G allele as well as the GG genotype in endurance athletes. Our result suggests that this is the case also in professional soccer players.

#5 An unusual knee mass in a soccer player
Reference: Asian J Sports Med. 2014 Sep;5(3):e23187. doi: 10.5812/asjsm.23187. Epub 2014 Sep 11.
Authors: Khodaee M, Roy D, VanBaak K, Bafus BT
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Summary: Non-traumatic knee joint effusion and fullness is a relatively common presenting complaint among athletes and non-athletes. Due to its broad differential diagnosis, a comprehensive evaluation beginning with history and physical examination are recommended. Imaging including plain radiography, magnetic resonance imaging (MRI), and in some cases ultrasound are preferred modalities. If inflammatory arthritis is suspected, joint aspiration and analysis may help diagnosis. A 37-year-old male soccer player presented with a complaint of left anterior knee pain and fullness for a few months. Physical examination revealed a healthy appearing male with obvious fullness of his left suprapatellar pouch and posterolateral knee. Plain radiographs were unremarkable. MRI demonstrated an effusion infiltrated by multiple, low intensity projections from a fatty mass in the suprapatellar pouch consistent with lipoma arborescens. Lipoma arborescens is a rare synovial disorder characterized by replacement of subsynovial tissue with mature fat cells, most commonly in the knee joint. MRI is the best diagnostic modality to evaluate and confirm the diagnosis as well as rule out other pathologies. More recent single case-reports and clinical series endorse arthroscopic synovectomy as the treatment of choice.

#6 Visual Search Strategies of Soccer Players Executing a Power vs. Placement Penalty Kick
Reference: PLoS One. 2014 Dec 17;9(12):e115179. doi: 10.1371/journal.pone.0115179. eCollection 2014.
Authors: Timmis MA, Turner K, van Paridon KN
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Summary: When taking a soccer penalty kick, there are two distinct kicking techniques that can be adopted; a 'power' penalty or a 'placement' penalty. The current study investigated how the type of penalty kick being taken affected the kicker's visual search strategy and where the ball hit the goal (end ball location). Wearing a portable eye tracker, 12 university footballers executed 2 power and placement penalty kicks, indoors, both with and without the presence of a goalkeeper. Video cameras were used to determine initial ball velocity and end ball location. When taking the power penalty, the football was kicked significantly harder and more centrally in the goal compared to the placement penalty. During the power penalty, players fixated on the football for longer and more often at the goalkeeper (and by implication the middle of the goal), whereas in the placement penalty, fixated longer at the goal, specifically the edges. Findings remained consistent irrespective of goalkeeper presence. Findings indicate differences in visual search strategy and end ball location as a function of type of penalty kick. When taking the placement penalty, players fixated and kicked the football to the edges of the goal in an attempt to direct the ball to an area that the goalkeeper would have difficulty reaching and saving. Fixating significantly longer on the football when taking the power compared to placement penalty indicates a greater importance of obtaining visual information from the football. This can be attributed to ensuring accurate foot-to-ball contact and subsequent generation of ball velocity. Aligning gaze and kicking the football centrally in the goal when executing the power compared to placement penalty may have been a strategy to reduce the risk of kicking wide of the goal altogether.

#7 Altered Lower Extremity Movement Variability in Female Soccer Players During Side-Step Cutting After Anterior Cruciate Ligament Reconstruction
Reference: Am J Sports Med. 2014 Dec 15. pii: 0363546514560153. [Epub ahead of print]
Authors: Pollard CD, Stearns KM, Hayes AT, Heiderscheit BC
Summary: Anterior cruciate ligament (ACL) reconstruction (ACLR) is common after an ACL tear and is thought to restore functional stability to the knee. A recent investigation demonstrated that individuals who have undergone ACLR exhibited increased lower extremity coupling variability during gait, suggestive of altered dynamic stability. However, little is known about whether they exhibit alterations in lower extremity variability during dynamic sport-specific tasks. To determine if female soccer players who have had an ACLR demonstrate differences in lower extremity coupling variability as compared with athletes with no history of knee injury during a side-step cutting maneuver. Controlled laboratory study. Ten female soccer players who had undergone ACLR served as the experimental group, and 10 female soccer players with no history of knee ligament injury composed the control group (CON). Three-dimensional kinematics and ground-reaction forces were collected while each participant performed a side-step cutting maneuver. Based on known ACL loading patterns, 7 lower extremity intralimb couplings were created. With use of a vector-coding technique, the coordination variability was calculated for each coupling. Independent t tests were used to determine group differences in variability for each coupling (P ≤ .05). Individuals who had undergone ACLR exhibited increased lower extremity variability during side-step cutting as compared with control subjects in the following couplings: hip rotation/knee abduction-adduction (27.2° ± 11.5° [ACLR] vs 19.7° ± 6.8° [CON]; P = .04), hip flexion-extension/knee abduction-adduction (26.0° ± 13.3° [ACLR] vs 18.6° ± 5.3° [CON]; P = .05), knee abduction-adduction/knee flexion-extension (13.5° ± 5.7° [ACLR] vs 7.3° ± 2.7° [CON]; P < .01), and knee abduction-adduction/knee rotation (26.4° ± 10.8° [ACLR] vs 19.3° ± 4.5° [CON]; P = .03). In addition, there was a trend toward increased variability in the hip rotation/ankle inversion-eversion coupling (22.9° ± 9.3° [ACLR] vs 18.0° ± 6.7° [CON]; P = .09) and knee abduction-adduction/ankle inversion-eversion coupling (25.9° ± 10.0° [ACLR] vs 20.2° ± 9.7° [CON]; P = .10). Female soccer players who have undergone ACLR and returned to sports participation exhibit altered lower extremity coupling variability during side-step cutting. While individuals who have had an ACLR exhibit mechanical knee stability before returning to sports, the observed increased movement variability during side-step cutting is likely reflective of altered neuromuscular control and may contribute to the known increased risk for ACL reinjury and knee osteoarthritis after return to sports participation. Improving the understanding of altered lower extremity coupling variability after ACLR will aid in the development of more effective rehabilitation programs.

#8 MRI findings in soccer players with long-standing adductor-related groin pain and asymptomatic controls
Reference: Br J Sports Med. 2014 Dec 15. pii: bjsports-2014-093710. doi: 10.1136/bjsports-2014-093710. [Epub ahead of print]
Authors: Branci S, Thorborg K, Bech BH, Boesen M, Nielsen MB, Hölmich P
Summary: Soccer players are commonly affected by long-standing adductor-related groin pain (ARGP), but the clinical significance of MRI findings in these athletes is largely unknown. Our aims were (1) to evaluate whether MRI findings are associated with long-standing ARGP in soccer players, (2) to assess MRI findings in asymptomatic soccer players and non-soccer playing controls. This cross-sectional study included 28 male soccer players with long-standing ARGP, 17 male asymptomatic soccer players and 20 male asymptomatic non-soccer playing athletes of matching age and athletic exposure. Participants underwent identical standardised and reliable clinical examination, and MRI scans (3 T) of the pelvis performed by a blinded observer. Images were consensus rated by three blinded radiologists according to a standardised MRI evaluation protocol. The associations between clinical adductor-related findings and pathological MRI findings were investigated with χ2 statistics and OR. Central disc protrusion (p=0.027) and higher grades of pubic bone marrow oedema (BMO; p=0.027) were significantly more present in symptomatic players than asymptomatic players. However, up to 71% of asymptomatic soccer players displayed different positive MRI findings, and asymptomatic soccer players had significantly higher odds (OR ranging from 6.3 to 13.3) for BMO, adductor tendinopathy and degenerative changes than non-soccer players. ARGP in soccer players was associated with central disc protrusion and higher grades of pubic BMO. Moreover, positive MRI findings were significantly more frequent in soccer players compared with non-soccer players irrespective of symptoms, suggesting that these MRI changes may be associated with soccer play itself rather than clinical symptoms.

#9 Comparison of physical performance among Brazilian elite soccer players of different age-categories
Reference: J Sports Med Phys Fitness. 2014 Dec 11. [Epub ahead of print]
Authors: Kobal R, Loturco I, Gil S, Cavinato Cal Abad C, Cuniyochi R, Barroso R, Tricoli V
Summary: The purpose of this study was to compare the physical performance (i.e., strength, power, speed and endurance) between Brazilian elite soccer players from different categories of the same club: professionals (PRO), under--20 (U--20), and under--17 (U--17). Seventy-one soccer players from three categories (PRO=24; U--20=21 and U--17=26) were assessed at the beginning of pre--season. Before the tests, they were familiarized with all experimental procedures. Squat jump (SJ), countermovement jump (CMJ), sprint (10m/20m), maximum dynamic strength (1RM), and Yo--Yo intermittent recovery tests level 1 were performed in three non--consecutive sessions. No significant differences were found between the categories for sprint times. The PRO players presented higher outcomes in the 1RM, SJ, CMJ, and Yo--Yo tests than the U--20 and U--17 players (P≤0.05). No significant differences were found between the U--20 and U--17 players in 1RM, and SJ/CMJ heights. The U--20 presented superior performance than the U--17 in the Yo--Yo test (P≤0.05). The findings indicated that PRO performed better than younger players in all assessments, except for the sprint tests. This may have been possible due to the differences inì training experience, technical expertise and individual levels of strength/power. However, the absence of differences between the U--20 and U--17 groups highlighted the necessity of developing specific training strategies in order to improve the physical capacities of younger players, throughout the maturation process. Moreover, due to the importance of sprinting in soccer, it is strongly recommended that fitness coaches develop more effective strategies to improve speed ability in professional players.

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