Latest research in football - week 23 - 2013

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 abstracts of studies were retrieved for this week:

#1 Inspiratory muscle training improves exercise tolerance in recreational soccer players without concomitant gain in soccer specific fitness
Authors: Guy JH, Edwards AM, Deakin GB.
Reference: J Strength Cond Res. 2013 May 29. [Epub ahead of print]Source
Summary: This study investigated whether the addition of inspiratory muscle training (IMT) to an existing programme of pre-season soccer training would augment performance indices such as exercise tolerance and sports-specific performance beyond the use of pre-season training alone. Thirty one adult males were randomised across three groups: experimental (EXP: n=12), placebo (PLA: n=9), and control (CON: n=10). EXP and PLA completed a 6-week pre-season programme (two x weekly sessions) in addition to concurrent IMT with either a IM training load (EXP) or negligible (PLA) inspiratory resistance. CON did not use an IMT device or undertake soccer training. All participants performed the following tests before and after the 6-week period: Standard spirometry; maximal inspiratory mouth pressure (MIP); multi stage fitness test (MSFT) and a soccer specific fitness test (SSFT). Following 6-weeks training, EXP significantly improved: MIP (P=0.002); MSFT distance covered (P=0.02); and post SSFT blood lactate (BLa) (P=0.04). No other outcomes from the SSFT were changed. Pre to post training performance outcomes for PLA and CON were unchanged. These findings suggest the addition of IMT to pre-season soccer training improved exercise tolerance (MSFT distance covered) but had little effect on soccer specific fitness indices beyond a slightly reduced post-training SSFT BLa. In conclusion, there may be benefit for soccer players to incorporate IMT to their pre-season training but the effect is not conclusive. It is likely that a greater pre-season training stimulus would be particularly meaningful for this population if fitness gains are a priority and also evoke a stronger IMT response.

#2 Soccer ball related posterior segment closed-globe injuries in outdoor amateur players
Authors: Gökçe G, Ceylan OM, Erdurman FC, Durukan AH, Sobacı G.

Reference: Ulus Travma Acil Cerrahi Derg. 2013 May;19(3):219-22. doi: 10.5505/tjtes.2013.74050.
Summary: The aim of this study is to report the characteristics, treatment, and anatomical and functional outcomes of outdoor amateur soccer players with soccer ball-related posterior segment ocular trauma. We conducted a retrospective chart review of 22 patients with diagnoses of closed-globe ocular trauma caused by soccer play activity from 2004 through 2008. Injuries were classified according to Ocular Trauma Classification. All patients (n=22) were male, and all injuries were caused by contact with the soccer ball itself. Sixteen (72%) patients did not require any treatment. Surgery was performed on 5 (22%) patients. Twenty (91%) patients had 5/200 or better visual acuity (VA) at presentation and 2 (9%) had hand movements or worse VA. At the final visit, all patients had 5/200 or better VA (p<0.01). A soccer ball can cause significant posterior segment trauma, and using eye protection equipment might be an appropriate solution.

#3 Performance and Muscle Architecture Comparisons between Starters and Non-Starters in NCAA Division I Women's Soccer
Authors: Jajtner AR, Hoffman JR, Scanlon TC, Wells AJ, Townsend JR, Beyer KS, Mangine GT, McCormack WP, Bohner JD, Fragala MS, Stout JR.
Reference: J Strength Cond Res. 2013 May 27. [Epub ahead of print]
Summary: This study compared performance and muscle architecture changes in starters (S) and non-starters (NS) during a National Collegiate Athletic Association Division I women's soccer season. Twenty-eight women (19.9±1.1y; 1.71±0.08m; 64.7±6.4kg) were monitored for vertical jump power (VJP), repeated line drills (LD), 3-dimensional multiple object tracking (3D-MOT), and reaction time (RT) at pre-, mid- and postseason. Muscle architecture (MA) changes using ultrasonography were assessed at pre- and postseason. Comparisons between S (n=11; 70.0±14.6min·game) and NS (n=17; 8.4±8.0min·game) were performed to make magnitude-based inferences. No differences were seen in VJP during the season in either group. S were more likely (81.1%) to decrease LD time than NS, with no differences in fatigue rate. S and NS improved 3D-MOT (1.14±0.41 to 1.55 ± 0.43) and RT (0.37±0.05s to 0.34±0.33s), with no differences between groups. Rectus femoris (RF) echo intensity improved (65.57±1.50 to 61.26±1.59) in both groups, with no interactions observed. Cross-sectional area (20.84±3.58 cm to 21.46±3.66 cm) increased, and pennation angle (PANG) (12.58±2.56° to 11.78±2.03°) decreased for both groups in the vastus lateralis (VL). MA comparisons between groups revealed S likely decreased VL muscle thickness (MT) and PANG (81.6%; 79.4% respectively), and possibly decreased RF MT and PANG (65.7%; 59.4% respectively) when compared to NS. Results indicate VJP and LD fatigue rate are not changed during a competitive season, but S become faster than NS. 3D-MOT and RT improve regardless of playing time. Changes in MA indicate practices alone provide sufficient stimulus for improving muscle quality during the competitive season.

#4 Offensive sequences in youth soccer: effects of experience and small-sided games
Authors: Almeida CH, Ferreira AP, Volossovitch A.
Reference: J Hum Kinet. 2013 Mar 28;36:97-106. doi: 10.2478/hukin-2013-0010. Print 2013 Mar.
Summary: The present study aimed to analyze the interaction and main effects of deliberate practice experience and small-sided game format (3 vs. 3 and 6 vs. 6 plus goalkeepers) on the offensive performance of young soccer players. Twenty-eight U-15 male players were divided into 2 groups according to their deliberate practice experience in soccer (i.e., years of experience in federation soccer): Non-Experienced (age: 12.84 ± 0.63 years) and Experienced (age: 12.91 ± 0.59 years; experience: 3.93 ± 1.00 years). The experimental protocol consisted of 3 independent sessions separated by one-week intervals. In each session both groups performed each small-sided game during 10 minutes interspersed with 5 minutes of passive recovery. To characterize the recorded offensive sequences we used the Offensive Sequences Characterization System, which includes performance indicators previous applied in other studies. No interaction effects on the offensive performance were found between both factors. Non-parametric MANOVA revealed that the factor "experience level" had a significant effect (p<0.05) on performance indicators that characterize the development of offensive sequences, especially in 6 vs. 6 + GKs. While experienced players produced longer offensive sequences with greater ball circulation between them, the non-experienced participants performed faster offensive sequences with a predominance of individual actions. Furthermore, significant differences were observed (p<0.05) in the development and finalization of offensive sequences within each group, when comparing small-sided game formats. Evidence supports that small-sided games can serve several purposes as specific means of training. However, the manipulation of game format should always consider the players' individual constraints.


#5 Bilateral and unilateral asymmetries of isokinetic strength and flexibility in male young professional soccer players
Authors: Daneshjoo A, Rahnama N, Mokhtar AH, Yusof A.
Reference: J Hum Kinet. 2013 Mar 28;36:45-53. doi: 10.2478/hukin-2013-0005. Print 2013 Mar.
Summary: This study investigated bilateral and unilateral asymmetries of strength and flexibility in male young professional soccer players. Thirty-six soccer players (age: 18.9 ± 1.4 years) participated in this study. A Biodex Isokinetic Dynamometer was used to assess the hamstring and quadriceps strength at selected speeds of 60°/s, 180°/s and 300°/s. Hip joint flexibility was measured using a goniometer. No difference was observed in conventional strength ratio, dynamic control ratio and fast/slow speed ratio between the dominant and non-dominant legs (p>0.05). All but one of the players (97.2%) had musculoskeletal abnormality (bilateral imbalance > 10%) in one or more specific muscle groups. The dominant leg had greater hip joint flexibility compared with the non-dominant leg (108.8 ± 10.7° versus 104.6 ± 9.8°, respectively). The findings support the hypothesis that physical performance and movement pattern experienced during soccer playing may negatively change the balance of strength in both legs (bilateral strength balance), but not on the same leg of the young male professional soccer players. The results can be helpful for trainers and coaches to decide whether the players need to improve their balance and strength which in turn may prevent injury. It is suggested that in professional soccer training, quadriceps and hamstrings muscle strength, as well as hip joint flexibility should not be overlooked.



#6 Short-term high intensity plyometric training program improves strength, power and agility in male soccer players
Authors: Váczi M, Tollár J, Meszler B, Juhász I, Karsai I.
Reference: J Hum Kinet. 2013 Mar 28;36:17-26. doi: 10.2478/hukin-2013-0002. Print 2013 Mar.
Summary: The aim of the present study was to investigate the effects of a short-term in-season plyometric training program on power, agility and knee extensor strength. Male soccer players from a third league team were assigned into an experimental and a control group. The experimental group, beside its regular soccer training sessions, performed a periodized plyometric training program for six weeks. The program included two training sessions per week, and maximal intensity unilateral and bilateral plyometric exercises (total of 40 - 100 foot contacts/session) were executed. Controls participated only in the same soccer training routine, and did not perform plyometrics. Depth vertical jump height, agility (Illinois Agility Test, T Agility Test) and maximal voluntary isometric torque in knee extensors using Multicont II dynamometer were evaluated before and after the experiment. In the experimental group small but significant improvements were found in both agility tests, while depth jump height and isometric torque increments were greater. The control group did not improve in any of the measures. Results of the study indicate that plyometric training consisting of high impact unilateral and bilateral exercises induced remarkable improvements in lower extremity power and maximal knee extensor strength, and smaller improvements in soccer-specific agility. Therefore, it is concluded that short-term plyometric training should be incorporated in the in-season preparation of lower level players to improve specific performance in soccer.



#7 Crossvalidation of two 20-m shuttle-run tests for predicting v[combining dot above]o2max in female collegiate soccer players
Authors: Green MS, Esco MR, Martin TD, Pritchett RC, McHugh AN, Williford HN.
Reference: J Strength Cond Res. 2013 Jun;27(6):1520-8. doi: 10.1519/JSC.0b013e318270fcc0.
Summary: The aim of this study was twofold: (a) to compare the maximal attained speed (MAS) from the 20-m shuttle (MST) and 20-m square-shuttle (SST) tests and (b) to crossvalidate 2 equations for predicting maximal oxygen consumption (V[Combining Dot Above]O2max) that were previously developed from MST and SST in a group of female collegiate soccer players. Thirty-nine subjects (age: 20.1 ± 1.5 years) participated in the study. A maximal graded exercise treadmill test was used to measure V[Combining Dot Above]O2max. In addition, V[Combining Dot Above]O2max was predicted from the MAS obtained during MST (predV[Combining Dot Above]O2maxMST) and SST (predV[Combining Dot Above]O2maxSST) using previously developed equations. Measured V[Combining Dot Above]O2max for the group was 44.2 ± 3.3 ml·kg·min. The MAS was 12.5 ± 0.6 km·h for MST and 13.3 ± 0.8 km·h for SST (p < 0.05). The prediction methods yielded a predV[Combining Dot Above]O2maxMST of 49.6 ± 3.9 ml·kg·min and predV[Combining Dot Above]O2maxSST of 41.8 ± 3.1 ml·kg·min, which were significantly different from measured V[Combining Dot Above]O2max (p < 0.05). The validity statistics revealed the following constant error (CE), correlation coefficient (r), standard error of estimate (SEE), and total error (TE) for predV[Combining Dot Above]O2maxMST and predV[Combining Dot Above]O2maxSST: CE = 5.35 ± 3.83, r = 0.45 (p < 0.05), SEE = 2.97 ml·kg·min, TE = 6.39 ml·kg·min; and CE = -2.43 ± 2.49, r = 0.69 (p < 0.05), SEE = 2.39 ml·kg·min, TE = 3.43 ml·kg·min, respectively. Residual plots indicated no proportional bias for either prediction model. The results of this study suggest that female collegiate soccer players had a higher MAS from SST compared with that from MST. In addition, SST appeared to be a more accurate predictor of V[Combining Dot Above]O2max than MST in the group of athletes.


#8 Association of lower limb injury with boot cleat design and playing surface in elite soccer
Reference: O'Connor AM, James IT.
Authors: Foot Ankle Clin. 2013 Jun;18(2):369-80. doi: 10.1016/j.fcl.2013.02.012.
Summary: Reducing external injury risk factors associated with the boot-surface interaction is important in reducing the incidence and severity of foot and ankle injury. A review of prospective football (soccer) injury epidemiology studies determined that the incidence of noncontact ankle sprain injury is relatively high. Research on the impact of cleat shape and configuration and boot design on the boot-surface interaction is providing new understanding of the impact on player biomechanics and injury risk but is not keeping pace with commercial advances in boot design and innovation in natural and synthetic turf surface technology.

#9 Football Injuries in Children and Adolescent Players: Are There Clues for Prevention?
Authors: Faude O, Rößler R, Junge A.
Reference: Sports Med. 2013 May 31. [Epub ahead of print]
Summary: Football (soccer) is the world's most popular sport with most players being younger than 18 years. Playing football can induce beneficial health effects, but there is also a high risk of injury. Therefore, it is necessary to implement measures for preventing injuries. The present review analyzes and summarizes published scientific information on the incidence and characteristics of football injuries in children and adolescent players to arrive at sound conclusions and valid considerations for the development of injury-prevention programs. A literature search was conducted up to November 2012. Fifty-three relevant scientific publications were detected. Thirty-two studies fulfilled the inclusion criteria for pooled analysis. Additional information from the remaining 21 studies was considered where appropriate to obtain a broader perspective on the injury problem in children and youth football. Training injury incidence was nearly constant for players aged 13-19 years, ranging from 1 to 5 injuries per 1,000 h training. Match injury incidence tended to increase with age through all age groups, with an average incidence of about 15 to 20 injuries per 1,000 match hours in players older than 15 years. Between 60 and 90 % of all football injuries were classified as traumatic and about 10-40 % were overuse injuries. Most injuries (60-90 %) were located at the lower extremities with the ankle, knee, and thigh being mostly affected. The frequency of upper-extremity and head/face injuries was higher in those studies that analyzed match injuries only. The most common injury types were strains, sprains, and contusions (10 up to 40 % each). There is some evidence that the risk of traumatic injuries and, in particular, of sustaining a fracture, contusion, or concussion was higher during match play than in practice sessions. Fractures were more frequent in children younger than 15 years than in older players. About half of all time-loss injuries led to an absence from sport of less than 1 week, one third resulted in an absence between 1 and 4 weeks, and 10 to 15 % of all injuries were severe. Separate data for players under the age of 11 years are almost absent. Maturation status seems to have an influence on injury characteristics, although evidence is not conclusive at this time. Three main areas seem to be of particular relevance for future prevention research in young football players: (1) the substantial number of severe contact injuries during matches, (2) the high number of fractures in younger players, and (3) the influence of maturation status and growth spurts.

#10 Interpersonal dynamics: 1v1 sub-phase at sub-18 football players
Authors: Clemente FM, Couceiro MS, Martins FM, Dias G, Mendes R.
Reference: J Hum Kinet. 2013 Mar 28;36:179-89. doi: 10.2478/hukin-2013-0018. Print 2013 Mar.
Summary: The performance of football players within game context can be analyzed based on their ability to break or (re)balance the attacker-defender dyad. In this context, the analysis of each sub-phase (e.g., 1v1, 2v2) presents a feature that needs to be taken into account in sports analysis. This study aims to investigate the interpersonal dynamics dyad formed by the attacker and the defender in 1v1 situations with a goalkeeper. A sample of 11 football male players (age: 17.91 ± 1.04 years) with 8.6 ± 1.52 years of practice experience participated in the study. Analyzing the 1v1 sub-phase, results show that the distance, speed and angular amplitude between the attacker and the defender increases, especially when the attacker attempts to overtake the defender (i.e., score a goal). We conclude that decision-making emerges from the perception that players draw from the action, actively and consistently interacting to find solutions to emerging problems within the game context.

#11 Effect of High-Speed Treadmill Training With a Body Weight Support System in a Sport Acceleration Program With Female Soccer Players
Authors: Wayne J, Eastman CS, Feland JB, Mitchell UH, Mortensen BB, Eggett D
Reference: J Str Cond Res June 2013 - Volume 27 - Issue 6 - p 1496-1502 doi: 10.1519/JSC.0b013e31826cac04
Summary: Maximum running speed and acceleration are essential components in many sports. The identification of specific training protocols to maximize sprint speed would be useful knowledge for coaches and players. The purpose of this study was to determine the effect of a high-speed treadmill (HST) with the use of a body weight support (BWS) system in a 6-week sport acceleration program (SAP) on female soccer athlete’s 40-yard sprint time and maximal isometric knee flexor and extensor strength. Two treatment groups and one control group were created. Both treatment groups participated in a 12-session SAP. The first treatment group (n = 12) used a BWS system while running on a HST; the second group (n = 12) used a standard treadmill (ST) with no BWS system. The participants of the control group (n = 8), NT, did not participate in a sports acceleration program and did not alter their exercise routines outside of the study. An analysis of covariance was performed using baseline measures as the covariate. The 40-yard sprint times for both treatment groups were shown to improve significantly compared with the control group (p < 0.001). Isometric knee flexor strength showed a greater increase in the ST group (p = 0.026) than in the other 2 groups, whereas knee extensor strengths did not show significant differences between treatment groups and control group (p > 0.05). Participants in the ST group had a much higher rate (66%) of shin splints and foot pain throughout the study than those in the HST (8%) and NT (0%) groups. These results can help high school coaches and athletes determine the optimal treadmill training regime.


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